Download Butorphanol-Mediated Antinociception in Mice: Partial Agonist

0022-3565/97/2823-1253$03.00/0
THE JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Copyright © 1997 by The American Society for Pharmacology and Experimental Therapeutics
JPET 282:1253–1261, 1997
Vol. 282, No. 3
Printed in U.S.A.
Butorphanol-Mediated Antinociception in Mice: Partial Agonist
Effects and Mu Receptor Involvement1,2
H. R. GARNER,3 TIMOTHY F. BURKE,4 C. DAVID LAWHORN,5 JOANNE M. STONER and WILLIAM D. WESSINGER
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock, Arkansas
Accepted for publication May 23, 1997
Clinically, opioids are most commonly used to provide relief of moderate-to-severe pain. The analgesics used for this
purpose are predominantly mu agonists, although some effective analgesics possess significant activity at other opioid
receptors. A vast number of analogs and congeners have been
synthesized in an attempt to obtain compounds that retain
the analgesic properties of morphine but have fewer adverse
effects and lower abuse liability. Although these efforts have
not resulted in the development of the “ideal opioid,” they
have generated numerous unique compounds that vary
widely in terms of opioid receptor-related properties such as
selectivity, affinity and intrinsic efficacy. In addition to possessing substantial clinical utility, a number of these synthetic compounds have been instrumental in advancing basic
Received for publication November 20, 1996.
1
A preliminary report of these findings was presented at the International
Anesthesiology Research Society (IARS) meeting in Washington, DC, March
1996.
2
This study was supported by the Division of Pediatric Anesthesia, Department of Anesthesiology, University of Arkansas for Medical Sciences, Little
Rock, AR, and the UAMS Graduate Student Research Fund. H.R.G. was
supported by a predoctoral fellowship funded by NIDA Training Grant
DA07260.
3
Present address: Johns Hopkins University School of Medicine, Behavioral Pharmacology Research Unit, 5510 Nathan Shock Dr., Suite 3000, Baltimore, MD 21224.
4
Present address: Astra Merck, Inc., 3838 N. Causeway Blvd., Lakeway III,
Ste. 2400, Metairie, LA 70002.
5
Present address: 4401 Heritage Dr., Lawrence, KS 66047.
effects of butorphanol in a dose-dependent insurmountable
manner. Pretreatment with nor-binaltorphimine (32 mg/kg), a
kappa-selective antagonist, did not reliably antagonize butorphanol, and naltrindole (20 and 32 mg/kg), a delta-selective
antagonist, failed to antagonize the effects of butorphanol. Low
doses of butorphanol (1.0, 1.8 or 3.2 mg/kg) caused parallel,
rightward shifts in the dose-effect curve for morphine and parallel leftward shifts in the dose-effect curve for U50,488H.
Taken together, the results of the present study suggest that
butorphanol is a partial agonist in the mouse radiant-heat tailflick test and that activity at mu receptors accounts for the
majority of its antinociceptive effects.
research knowledge of opioid mechanisms. Some synthetic
compounds, such as butorphanol and buprenorphine, appear
to have “mixed” opioid actions; that is, they act as agonists or
antagonists at multiple opioid receptors. Butorphanol is a
widely used and potent analgesic with lower, although still
significant, abuse potential than morphine and fentanyl
(Brown, 1985; Evans et al., 1985; Smith and Davis, 1984).
Over the past few years, butorphanol has gained increased
clinical importance as an analgesic, a fact made clear by its
recent release in a transnasal formulation (Shyu et al., 1993).
Moreover, it was recently reported that butorphanol is effective in preventing the adverse side effects associated with
morphine use in adults (Lawhorn et al., 1991) and in children
(Lawhorn and Brown, 1994), suggesting that the antagonist
actions of butorphanol can also have a clinical benefit.
Butorphanol exhibits both mu and kappa agonist actions
depending on the animal species and experimental conditions used (e.g., Butelman et al., 1995; Dykstra, 1990; Preston and Bigelow, 1994). In radioligand binding experiments
in monkey brain, butorphanol displaces mu, kappa and delta
opioids with .10-fold binding selectivity for mu vs. kappa
and .30-fold mu vs. delta selectivity (Butelman et al., 1995).
A similar profile of binding selectivity was observed in rodent
brain (Chen et al., 1992; Horan and Ho, 1989). Moreover,
butorphanol is characterized as a low efficacy or partial agonist and exhibits antagonist action at mu and kappa recep-
ABBREVIATIONS: %MPE, % maximum possible effect; b-FNA, b-funaltrexamine; nor-BNI, nor-binaltorphimine; CL, confidence limit.
1253
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
ABSTRACT
In the present experiments, we characterized the agonist and
antagonist effects of butorphanol in mice. In the mouse radiantheat tail-flick test, the mu agonists morphine and fentanyl and
the kappa agonist U50,488H were fully effective as analgesics,
whereas butorphanol was partially effective (producing 82% of
maximal possible analgesic effect). Naltrexone was approximately equipotent in antagonizing the effects of morphine, fentanyl and butorphanol; in vivo apparent pA2 values for these
naltrexone/agonist interactions were 7.5 (unconstrained). Naltrexone was ;10 times less potent in antagonizing the effect of
U50,488H (average apparent pKB 5 6.7). The selective mu
antagonist b-funaltrexamine (0.1–1.0 mg/kg) antagonized the
1254
Garner et al.
in the presence of different doses of the antagonist. A less
widely used analysis, the apparent pKB analysis, requires
the determination of an agonist dose-effect curve in the presence of only one dose of the antagonist (Negus et al., 1993).
Like the apparent pA2 analysis, the apparent pKB analysis is
used to compare the potency of antagonists in blocking the
effects of agonists, but it is typically used in situations in
which it is not possible to redetermine an agonist dose-effect
curve in the presence of multiple doses of the antagonist (e.g.,
limited supply of the antagonist). In the present study, these
analyses are used to compare the analgesic effects of morphine, fentanyl and U50,488H with those of butorphanol in
the mouse radiant-heat tail-flick test and to make inferences
about the receptor population or populations that mediate
these effects. To this end, the effects of the competitive antagonist naltrexone on the analgesic effects of these agonists
were examined in the mouse radiant-heat tail-flick test.
Another goal of the present study was to use highly specific
antagonists for mu, kappa and delta receptors (i.e., b-FNA,
nor-BNI or naltrindole, respectively) to further define the
receptor population that mediates the antinociceptive effects
of butorphanol. The development of opioid antagonists highly
specific for the mu, kappa and delta receptors has played a
critical role in distinguishing the individual opioid receptor
types that mediate the effects of various opioids (e.g., Broadbear et al., 1994; Sofuoglu et al., 1991; Spanagel et al., 1994;
Ward et al., 1982). In the mouse abdominal stretch test for
antinociception, b-FNA pretreatment produced a marked
rightward shift in the dose-effect curve for butorphanol, suggesting a major role for the mu receptor in its analgesic
actions (Zimmerman et al., 1987). However, other investigators have classified the analgesic effects of butorphanol as
being kappa mediated (e.g., Houde, 1979; Vogelsang and
Hayes, 1991). Given the uncertainty surrounding the mechanisms of the analgesic action of butorphanol, we examined
these effects after pretreatment with naltrexone, b-FNA,
nor-BNI or naltrindole in the mouse radiant-heat tail-flick
test. Finally, because it has been classified as a low efficacy
agonist with antagonist properties and because the antagonist effects of butorphanol may have clinical importance, the
ability of butorphanol to antagonize the analgesic effects of
morphine and U50,488H was also examined.
Methods
Animals. The animals were experimentally naive, male ND4
Swiss-Webster mice (Harlan Sprague Dawley, Indianapolis, IN). A
total of five mice were used for each point on all dose-effect curves
unless otherwise indicated. At the time of use, mice weighed ;25 to
30 g. Before use, mice had unlimited access to food (PMI Feed, St.
Louis, MO) and water and were housed in groups of five in a vivarium maintained on a normal phase 12-hr light/dark cycle.
Apparatus and antinociception tests. An adaptation of the
radiant-heat tail-flick procedure of D’Amour and Smith (1941) was
used. Analgesia testing was conducted with a tail-flick apparatus
(model TF-6; Emdie Instruments, Richmond, VA) that used a beam
of light as the thermal nociceptive stimulus. An animal’s tail was
positioned covering a photocell under the light beam. Illumination of
the light started an automatic timer. The lamp was extinguished and
the timer was stopped when the photocell was exposed after a mouse
“flicked” its tail out of the beam. The lamp automatically extinguished after 10 sec to prevent thermal injury to the tail. The
intensity of the lamp was adjustable and set so control tail-flick
reaction times fell within 2 to 4 sec in control measurements. A small
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
tors (e.g. Dykstra, 1990). For example, it has been reported
that in rhesus monkeys, the analgesic effects of butorphanol
are mediated by mu receptors, a finding supported by its
sensitivity to the antagonist effects of the competitive antagonist quadazocine and by an apparent pA2 value that has
been associated with activity at mu receptors (Butelman et
al., 1995). Conversely, in squirrel monkeys, butorphanol attenuates the antinociceptive effects of l-methadone (Dykstra,
1990), illustrating its antagonist actions at mu receptors.
Similarly, therapeutic doses of butorphanol can cause respiratory depression (Talbert et al., 1988), yet butorphanol has
also been reported to reverse the respiratory depressive effects of the selective mu agonist fentanyl (Bowdle et al.,
1987). Furthermore, butorphanol increases urinary output in
rats (Horan and Ho, 1989), whereas it antagonizes the increased diuretic effects of the kappa agonist bremazocine
(Leander 1983a, 1983b). Interestingly, in rhesus monkeys,
butorphanol is devoid of any diuretic effects, suggesting that
butorphanol has no kappa agonist effects in this species
(Butelman et al., 1995).
Because the mixed agonist/antagonist analgesics have activity at multiple opioid receptors, the question arises as to
which receptor mediates the effects of a particular opioid of
this class. An important step in the pharmacological classification of the effects of an opioid compound is the evaluation
of the sensitivity of these effects to antagonism by receptorselective antagonists. Several investigators have compared
the potency of competitive antagonists such as naloxone,
naltrexone and quadazocine in blocking various effects of
opioid agonists to make inferences about mechanisms of action. For example, in a study in which the response ratedecreasing effects of various opioid agonists were examined,
naltrexone is more potent as an antagonist of the effects of
morphine, a mu agonist, than of ethylketocyclazocine, a
kappa agonist (Harris, 1980). These results were interpreted
as evidence that the rate-decreasing effects of morphine and
ethylketocyclazocine are mediated by separate opioid receptor populations for which naltrexone has different affinities.
Analyses of results from this type of competitive antagonism
study has been broadened to include the in vivo apparent pA2
analysis (Tallarida et al., 1979). This analysis has been used
to determine homogeneity of receptor populations and make
inferences about agonists and antagonists with respect to the
pharmacological receptor through which they produce their
effects (Bertalmio and Woods, 1987; Shannon et al., 1986;
Walker et al., 1994; Wessinger and McMillan, 1986). The
apparent pA2 analysis provides a measure of the potency of
an antagonist in blocking the effects of an agonist and is
defined as the negative logarithm of the dose of the antagonist that produces a 2-fold rightward shift in the dose-effect
curve of the agonist alone. The differential affinity of the
competitive opioid antagonists for the mu, kappa and delta
opioid receptors renders this analysis a useful tool in characterizing the opioid receptor population through which a
particular effect is mediated. For example, in a study in
which the antinociceptive effects of various opioid compounds
in mice were examined, apparent pA2 values for naloxone in
combination with mu agonists were higher than pA2 values
for naloxone in combination with kappa agonists (Ward and
Takemori, 1983).
Determination of apparent pA2 values requires that the
dose-effect curve of an agonist be redetermined several times
Vol. 282
1997
Butorphanol Antinociception
% MPE 5
Test reaction time 2 control reaction time
3 100
10 sec 2 Control reaction time
After administration of an agonist or antagonist, if a mouse removed its tail faster than the control latency, a value of 0%MPE was
assigned. Group mean 6 S.E.M. values are presented and were
determined by averaging individual data from all mice tested under
a given condition. A test drug was considered to be fully effective if
$90%MPE was obtained.
Least-squares linear regression analysis of the linear portion of
the dose-effect curves was used to estimate the ED50 value, or the
dose that would be expected to result in 50%MPE. The slopes of the
dose-effect curves for the agonists in combination with antagonists
were compared with those of the agonists alone using a parallel line
assay (Tallarida and Murray, 1987). If slopes did not differ, apparent
pA2 values were determined by constructing Schild plots (Arunlakshana and Schild, 1959) using drug doses instead of drug concentrations (Takemori, 1974). The apparent pA2 value represents the dose
of the antagonist that would be expected to produce a 2-fold shift to
the right of the dose-effect curve for the agonist alone. For Schild plot
analysis, dose ratios were calculated by dividing the ED50 value of
each agonist in combination with each dose of naltrexone by the ED50
for each agonist alone. The log of the dose ratios 21 (log DR 2 1) was
plotted as a function of the negative log of the molar dose of the
antagonist (mol/kg). A regression line was fitted to these points.
Slopes of the Schild plots were considered different from unity if the
95% CL of the slope did not include 21. If the slopes of Schild
regression were not significantly different from unity, the regression
line was redetermined with the slope constrained to 21. The intercept of the Schild regression line on the abscissa is the apparent pA2
value. Apparent pA2 values from unconstrained and constrained
Schild plots are reported here for comparison.
In one instance, the slope of the regression line was determined to
be statistically different from 21 (i.e., dose-effect curves were not all
parallel to the initial control curves). In this case, an apparent pKB
value was calculated using a modification of the equation: DR 2 1 5
B/KB (Tallarida et al., 1979), where B is the antagonist dose in
mol/kg. Rearranging and taking the negative logarithm of both sides
yield the following equation for determining pKB: pKB 5 2log[B/
(DR 2 1)], where DR refers to the dose ratio. The apparent pKB value
is used to estimate the potency of an antagonist such as naltrexone
to attenuate the effect of various agonists (Kenakin, 1987).
Drugs. Morphine sulfate was obtained from Mallinkrodt (St.
Louis, MO). Butorphanol tartrate was a gift from Bristol-Myers
Squibb Pharmaceutical Research Institute (Princeton, NJ). Naltrexone hydrochloride and fentanyl hydrochloride were provided by the
National Institute on Drug Abuse (Rockville, MD). b-FNA, nor-BNI
and naltrindole, all as hydrochloride salts, were obtained from Tocris-Cookson (Langford, Bristol, UK). U50,488H (trans—(6)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)-cyclohexyl]benzeneacetamide
methanesulfonate hydrate) was generously supplied by The Upjohn
Co. (Kalamazoo, MI). Drugs were dissolved in 0.9% physiological
saline to an injection volume of 10 ml/kg. For nor-BNI to dissolve, a
drop of lactic acid was added to the solution. Doses administered are
expressed as mg/kg and refer to the salt, except in the apparent pA2
analyses, in which naltrexone doses were converted to mol/kg.
Results
Effects of agonists alone. Morphine, fentanyl, U50,
488H and butorphanol produced dose-dependent increases in
tail-flick latency (fig. 1). Maximal antinociception (i.e.,
.90%MPE) was observed after morphine, fentanyl and
U50,488H. The dose-effect curve for butorphanol in figure 1
is the mean of two determinations [from the naltrexone antagonism studies and from the selective antagonist studies].
The ED50 (95% CL) for this mean curve was 27.6 mg/kg
(19.7–38.8). Butorphanol, at the highest dose that could be
administered (100 mg/kg), produced only partial analgesia
(82%MPE). Doses of butorphanol of .100 mg/kg produced
convulsions and were lethal within ;2 to 5 min. High doses
of naltrexone (10 mg/kg) were unable to prevent this toxicity,
suggesting it was a nonopioid effect. Likewise, doses of
U50,488H of .180 mg/kg also produced convulsions and
were lethal in all mice within ;5 to 10 min. Again, high doses
of naltrexone (10 mg/kg) were unable to prevent this effect.
The relative order of potency of these agonists in the mouse
radiant-heat tail-flick test was fentanyl @ morphine .
U50,488H $ butorphanol.
Naltrexone antagonism of agonist effects. Naltrexone
pretreatment (0.003–1.0 mg/kg) produced dose-dependent,
parallel rightward shifts in the dose-effect curves for morphine, fentanyl and butorphanol alone (fig. 2, table 1). There
was a significant difference (at P , .01; 26 df) between the
slopes of the dose-effect curves for U50,488H alone and for
U50,488H plus 1.0 mg/kg naltrexone; however, the slopes of
the dose-effect curves for the other agonists (morphine, fentanyl or butorphanol) in combination with naltrexone were
Fig. 1. Antinociceptive effects of butorphanol, morphine, fentanyl and
U50,488H in the mouse radiant-heat tail-flick test. Antinociceptive effects were assessed 20 min after drug (intraperitoneally) administration
and are expressed as %MPE. All points represent mean 6 S.E.M.
values (n 5 5), except points on the butorphanol curve (n 5 10). The
butorphanol curve is the mean of the butorphanol curves shown in
figures 2 and 4.
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
number of animals (,2%) with control reaction times outside this
range were excluded from the study.
Mice were initially injected with saline; ;15 min later, a base-line
(control) reaction time was determined. Agonist dose-effect curves
were determined by the administration of fentanyl, morphine, butorphanol or U50,488H 20 min before redetermination of the tailflick reaction times. In antagonism experiments, a pretreatment
dose of the antagonist (naltrexone, b-FNA, nor-BNI or naltrindole)
was initially administered. After the appropriate antagonist pretreatment time (i.e., naltrexone, 20 min; naltrindole, 25 min; b-FNA
or nor-BNI, 24 hr), the tail-flick reaction time was measured and
then a dose of the agonist was administered. At 20 min after the
agonist injection, tail-flick reaction times were measured. Injections
of b-FNA, nor-BNI or naltrindole were administered subcutaneously,
whereas all other agonists and antagonists were administered intraperitoneally.
In other experiments, butorphanol (1.0, 1.8 or 3.2 mg/kg) was
administered before morphine or U50,488H. At 15 min later, the
tail-flick reaction time was measured, and then a dose of the agonist
was administered. At 20 min after administration of the agonist,
tail-flick reaction times were redetermined.
Data analysis. The analgesic response was calculated as %MPE
using the following equation:
1255
1256
Garner et al.
Vol. 282
not statistically different from parallel to the dose-effect
curve for the agonists alone. Doses of morphine of .560
mg/kg (e.g., 1000 mg/kg), administered after pretreatment
with 1.0 mg/kg naltrexone, were lethal to all animals.
Figure 3 shows the Schild plots for naltrexone as an antagonist of the antinociceptive effects of morphine, fentanyl
and butorphanol. Apparent pA2 values (determined from
Schild plots with the slopes unconstrained) for these interactions were 7.5. Table 2 shows the similar apparent pA2 values obtained from unconstrained and constrained Schild plot
analyses. Because naltrexone did not produce consistent parallel shifts in the U50,488H dose-effect curve, apparent pA2
values were not determined. However, to obtain an estimate
of the potency of naltrexone as an antagonist of the analgesic
effects of U50,488H, pKB values for each dose of naltrexone
(0.01, 0.1 and 1.0 mg/kg) in combination with U50,488H were
calculated. Apparent pKB values for U50,488H in combination with 0.01, 0.1 or 1.0 mg/kg naltrexone were 7.4, 6.6 and
6.2, respectively, and the average apparent pKB value was
6.7.
Antagonism of butorphanol effects with b-FNA, norBNI and naltrindole. Doses of 0.1, 1.0 and 10 mg/kg b-FNA
administered 24 hr before butorphanol produced a dose-related antagonism of the analgesic effects of butorphanol in
the mouse radiant-heat tail-flick test (fig. 4, top). Pretreatment with 0.1 mg/kg b-FNA produced a nonparallel, right-
Fig. 3. Schild plots for naltrexone as an antagonist of morphine (top),
fentanyl (middle) and butorphanol (bottom). Abscissae, negative logarithm of the molar doses of naltrexone (mol/kg); ordinates, logarithm of
the ratio of the ED50 for the agonist in the presence of the antagonist to
the ED50 of the agonist alone 21 (DR 2 1). The diagonal lines were fit
to the data points by linear regression and the intercept of the fitted line
is the apparent pA2 value. See text for further details.
ward shift in the dose-effect curve for butorphanol alone (at
P , .05, 31 df) and caused a decrease in the maximum
analgesic effect produced by higher doses of butorphanol (i.e.,
butorphanol alone produced 82%MPE; butorphanol plus 0.1
mg/kg b-FNA produced 64%MPE). The ED50 (95% CL) values
for butorphanol alone and butorphanol plus 0.1 mg/kg b-FNA
were 31.9 mg/kg (20.6–57.4) and 82.3 mg/kg (60.7–136.2),
respectively. Pretreatment with 1.0 mg/kg b-FNA produced a
further decrease in the maximum level of analgesic effect
(i.e., 37%MPE). Nearly complete antagonism of butorphanol
antinociception was achieved with 10 mg/kg b-FNA pretreatment (i.e., 17%MPE).
Pretreatment with 10 mg/kg nor-BNI produced a significant, ;2-fold, rightward shift in the dose-effect curve for
butorphanol alone (fig. 4, center). The ED50 (95% CL) values
for butorphanol alone and butorphanol plus 10 mg/kg norBNI were 31.9 mg/kg (20.6–57.4) and 74.4 mg/kg
(38.6–299.7), respectively. In contrast, a higher dose of norBNI, 32 mg/kg, failed to significantly shift the dose-effect
curve for butorphanol; the ED50 (95% CL) was 35.2 mg/kg
TABLE 1
ED50 (95% CL) values for the analgesic effects of opioid agonists alone and in combination with naltrexone in the mouse tail-flick
analgesic test
Naltrexone dose
Drug
Alone
0.003
0.01
0.1
1.0
57.3 (34.6–95.1)
0.46 (0.28–0.73)
100.9 (74.6–161.5)
33.9 (25.9–44.2)
319.7 (241.6–462.4)
3.2 (1.8–5.4)
mg/kg
Morphine
Fentanyl
Butorphanol
U50,488H
11.8 (8.7–16.7)
0.11 (0.09–0.13)
24.3 (14.2–45.8)
17.4 (12.6–23.9)
32.1 (5.2–220.4)
Data are from dose-effect curves shown in figure 2.
22.6 (16.5–31.1)
0.23 (0.19–0.29)
55.0 (34.1–128.7)
22.6 (16.8–30.4)
85.2 (69.1–100.8)
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
Fig. 2. Antinociceptive effects of the agonists morphine, fentanyl, butorphanol and U50,488H alone and after administration of various
doses (0.003–1.0 mg/kg) of the antagonist naltrexone (NTX). Naltrexone
was administered (intraperitoneally) 20 min before administration (intraperitoneally) of the agonists. Antinociceptive effects were assessed
20 min later and are expressed as %MPE. All points represent mean 6
S.E.M. values (n 5 5, unless otherwise indicated).
1997
Butorphanol Antinociception
TABLE 2
Apparent pA2 values (95% CL) and slopes for naltrexone
antagonism of the antinociceptive effects of opioid agonists in
the mouse tail-flick analgesic test
Agonist
Apparent pA2
(95% CL)
Slope
Apparent pA2
(95% CL) Slope
of 21.0
Morphine
Fentanyl
Butorphanol
7.5 (6.2–8.8)
7.5 (4.2–10.9)
7.5 (5.0–9.9)
20.73 (21.5–0.04)
20.69 (22.5–1.14)
20.62 (23.0–1.8)
7.2 (6.5–7.9)
7.2 (6.4–8.1)
7.5 (6.6–8.3)
Fig. 4. Antinociceptive effects of butorphanol alone and after the administration of the antagonists: b-FNA (top), nor-BNI (middle) and naltrindole (bottom). The same butorphanol dose-effect curve is depicted
in each panel. The antagonists were administered (subcutaneously) 24
hr (b-FNA or nor-BNI) or 25 min (naltrindole) before administration
(intraperitoneally) of butorphanol. Antinociceptive effects were assessed 20 min later and are expressed as %MPE. All points represent
mean 6 S.E.M. values (n 5 5).
trindole, the analgesic effects were 91.4%MPE and 78%MPE,
respectively.
Effects of morphine and U50,488H after low doses of
butorphanol. Pretreatment with slightly effective doses of
butorphanol (1.0, 1.8 or 3.2 mg/kg) produced dose-dependent,
parallel, rightward shifts (antagonism) in the dose-effect
curve for morphine alone (fig. 5, top). The ED50 (95% CL)
values for morphine alone or morphine in combination with
1.0, 1.8 or 3.2 mg/kg butorphanol were 13.6 mg/kg (9.9–19.7),
31.6 mg/kg (23.3–44.4), 58.3 mg/kg (42.1–81.3) and 82.1
mg/kg (47.7–127.7), respectively. In contrast, pretreatment
with 1.0 and 3.2 mg/kg butorphanol produced leftward, parallel shifts in the dose-effect curve for U50,488H alone, with
the shift produced by the higher dose of butorphanol (3.2
mg/kg) being significantly different from control (fig. 5, bottom). The ED50 (95% CL) values for U50,488H alone and
U50,488H in combination with 1.0 or 3.2 mg/kg butorphanol
were 27.8 mg/kg (17.1–42.0), 23.4 mg/kg (15.7–32.2) and 17.3
mg/kg (9.2–25.6), respectively.
Discussion
Many of the actions of butorphanol in the mouse radiantheat tail-flick test were consistent with those of a partial mu
agonist. In vivo apparent pA2 analyses showed that the interactions of naltrexone and butorphanol were similar to the
interactions of naltrexone with other mu agonists. b-FNA,
the selective mu antagonist, produced an insurmountable
antagonism of butorphanol analgesic effects, whereas antagonists specific for kappa or delta opioids produced inconsis-
Fig. 5. Effects of various doses of butorphanol administered 15 min
before morphine (top) or U50,488H (bottom). Antinociceptive effects
were assessed 20 min after morphine or U50,488H administration and
are expressed as %MPE. All drugs were administered intraperitoneally.
All points represent mean 6 S.E.M. values (n 5 5).
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
(21.7–70.9). Neither pretreatment dose of nor-BNI caused a
decrease in the maximum level of analgesic effect produced
by higher doses of butorphanol. The %MPE was 82% after
100 mg/kg butorphanol alone and 83% and 82% after 100
mg/kg butorphanol plus 10 or 32 mg/kg nor-BNI, respectively.
Pretreatment with naltrindole (20 or 32 mg/kg) had no
effect on the dose-effect curve for butorphanol alone (fig. 4,
bottom). The ED50 (95% CL) values for butorphanol in combination with 20 and 32 mg/kg naltrindole were 29.8 mg/kg
(17.7–44.8) and 41.5 mg/kg (28.2–61.2). Pretreatment with
naltrindole also had little effect on the maximum level of
antinociception produced by higher doses of butorphanol
alone. The analgesic effect of 100 mg/kg butorphanol alone
was 82%MPE, and in combination with 20 or 32 mg/kg nal-
1257
1258
Garner et al.
nist did not have differential affinity. It is also important to
note that the determination of apparent pA2 values is based
on several assumptions, including that the concentrations of
drugs at the receptor are directly proportional to the dose
administered, agonist and antagonist interact in a competitive manner and agonist and antagonist are in equilibrium
with the receptor. When the assumptions are met or approximated, the apparent pA2 analysis is fairly rigorous because
it incorporates data obtained using several doses of the antagonist. Failure to meet these assumptions empirically can
result in Schild plots that have slope significantly different
from 21. In this case, the apparent pA2 analysis is considered
inappropriate. An alternative to apparent pA2 analysis,
which is useful in situations in which requirements of the
Schild analysis cannot be met, is the calculation of apparent
pKB values (adapted from Tallarida et al., 1979) that can also
be used to estimate the potency of an antagonist such as
naltrexone to antagonize the effects of various agonists. This
method can be used, for example, when higher doses of the
agonist produce a nonopioid-mediated toxicity, making it unfeasible to redetermine the agonist dose-effect curve in the
presence of several doses of the antagonist. Comparing apparent pKB values for different agonist/antagonist interactions can implicate the involvement of a particular opioid
receptors agonist effects. Because antagonists such as naltrexone are more potent in antagonizing mu-mediated effects
as opposed to kappa-mediated effects, apparent pKB values
for the interaction between naltrexone and a mu agonist
should be higher than with a kappa agonist. Previous investigations show this to be the case. (Negus et al., 1993; Smith
and Picker, 1995). Although the apparent pA2 and apparent
pKB analyses both estimate antagonist potency, the apparent
pA2 analysis is more stringent and provides a measure of
variability. Thus, the apparent pA2 analysis should be the
analysis of choice provided the previously mentioned requirements can be met.
Naltrexone (0.003–1.0 mg/kg) was approximately equipotent in antagonizing the antinociceptive effects of morphine,
fentanyl and butorphanol, suggesting that these agonist/antagonist interactions are mediated through the same receptor, presumably the mu receptor. Apparent pA2 values for the
interactions between naltrexone and morphine, fentanyl or
butorphanol were identical (i.e., 7.5) and generally agree
with values obtained for naltrexone as an antagonist of mu
agonists in other assays (e.g., Dykstra et al., 1988; Walker
et al., 1994; Young et al.,, 1992). Furthermore, previous analysis of the naltrexone antagonism of the rate-decreasing effects of butorphanol in rats responding under a fixed ratio 30
schedule of food reinforcement yielded an apparent pA2 value
of 7.2 (Pitts et al., 1996). Naltrexone (0.01, 0.1 and 1.0 mg/kg)
produced dose-dependent rightward shifts in the dose-effect
curve for U50,488H; however, the dose-effect curve generated
by the highest dose of naltrexone in combination with
U50,488H was not parallel to the dose-effect curve for
U50,488H alone. Other investigators have shown that the
interaction between naltrexone and U50,488H is competitive
in nature and all shifts produced by increasing doses of
competitive antagonists were parallel to the dose-effect
curve for U50,488H alone (Dykstra, 1990; Takemori and
Portoghese, 1984). In current studies, near-lethal doses of
U50,488H ($100 mg/kg) were required to produce full analgesia in the mouse radiant-heat tail-flick test, thereby limit-
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
tent effects or were ineffective. The partial mu agonist effects
of butorphanol were also manifested by its antagonist actions
when low doses of butorphanol were combined with morphine. There was some evidence that actions of butorphanol
in the present studies could also be mediated by kappa receptors. First, the selective kappa antagonist nor-BNI was
effective in antagonizing the analgesic actions of butorphanol
at 10 mg/kg (however, it was not effective at 32 mg/kg).
Second, when low doses of butorphanol were combined with
doses of U50,488H, the dose-effect curve for U50,488H
shifted to the left, suggesting a coagonist effect.
Butorphanol was effective as an analgesic in the mouse
radiant-heat tail-flick test, but less-than-maximal analgesia
was obtained. It should be noted that the inability of butorphanol to produce maximal analgesic effects may have been
confounded by a ceiling effect in that doses of .100 mg/kg
were lethal. In other studies with assays in which efficacy
requirements are high (e.g., 55–56°C water in the tail-withdrawal test or a schedule of shock titration), butorphanol is
only partially or ineffective in producing analgesia (Butelman et al., 1995; Dykstra, 1990; Morgan and Picker, 1996;
O’Callaghan and Holtzman, 1975). In contrast, butorphanol
produces maximum analgesia in the mouse abdominal
stretch test (Zimmerman et al., 1987) and in the warm water
tail-withdrawal test when lower temperatures were used
(Butelman et al., 1995; Morgan and Picker, 1996). In current
studies, the selective mu agonists morphine and fentanyl
produced dose-related increases in antinociception and were
fully effective. This is consistent with other studies using
different animal models and high efficacy requiring assays
(Morgan and Picker, 1996; Walker et al., 1994; Ward and
Takemore, 1983). Likewise, U50,488H also produced doserelated increases in antinociception and maximal analgesia
(i.e., 100%MPE was obtained). This finding is in contrast to
previous investigations suggesting that kappa agonists are
not as effective as mu agonists in rodent analgesia assays
(Dykstra, 1985; Porreca et al., 1984; Upton et al., 1982);
however, it is consistent with reports that kappa agonists are
highly effective analgesics in rhesus monkeys (Dykstra et al.,
1987a, 1987b).
The antinociceptive effects of butorphanol were sensitive to
the antagonist effects of naltrexone and permitted the use of
in vivo apparent pA2 analysis for characterization of the
receptor populations through which butorphanol produces its
agonist effects (Dykstra et al., 1988; Shannon et al., 1986;
Takemori, 1974). Classification of agonists in terms of the
opioid receptor population through which they produce their
effects (i.e., analgesic, discriminative-stimulus, respiratory
depressive effects, etc.) is an important step in understanding tolerance and physical dependence (Feng et al., 1994;
Horan and Ho, 1991), drug interactions (Dykstra, 1990;
Young et al., 1992) and efficacy questions (Morgan and
Picker, 1996; Picker et al., 1990). If similar pA2 values for a
given antagonist against different agonists (either full or
partial) are obtained, then it is considered presumptive evidence that the agonist/antagonist interactions are mediated
through the same receptor population (e.g., Tallarida et al.,
1979). It should be emphasized that the utility of apparent
pA2 analyses in the present study depends on the differential
affinity of naltrexone for mu, kappa and delta opioid receptors; this approach would not be useful to distinguish between receptors or receptor subtypes for which the antago-
Vol. 282
1997
1259
of analgesia produced by butorphanol, suggesting that norBNI was not an irreversible or insurmountable antagonist of
the analgesic effects of butorphanol. Previous studies using
nor-BNI as an antagonist of the antinociceptive effects of mu
agonists such as morphine have shown that nor-BNI does not
cause a shift in the dose-effect curves for these agonists and
does not decrease the level of effect obtained under control
conditions (Broadbear et al., 1994; Horan et al., 1991). Finally, pretreatment with the delta-specific antagonist naltrindole (20 and 32 mg/kg) failed to antagonize the antinociceptive effects of butorphanol. In mice, naltrindole (20 mg/kg
s.c.) antagonizes the antinociceptive effects of the delta-selective agonist DSLET without affecting the analgesic effects
of morphine or U50,488H (Portoghese et al., 1988). Because
naltrindole did not antagonize the effects of butorphanol in
the present assay, it is unlikely that delta receptors play a
significant role in its analgesic effects.
Low doses of butorphanol in combination with morphine
produced antagonist-like effects. Pretreatment with butorphanol (1.0, 1.8 or 3.2 mg/kg) caused parallel, rightward
shifts in the dose-effect curve of morphine alone. This is
consistent with the expectation that a low efficacy agonist
would antagonize the effects of a higher efficacy agonist
when given in combination. These findings are similar to
those reported in a previous study in which butorphanol
antagonizes the antinociceptive effects of the mu agonist
l-methadone in monkeys (Dykstra, 1990). In contrast, low
doses of butorphanol in combination with U50,488H produced leftward shifts in the dose-effect curve of U50,488H
alone, suggesting that the antinociceptive effects of butorphanol “add to” those of U50,488H. This finding is consistent
with a previous report by Butelman et al., (1995) in which
butorphanol produced a nonparallel leftward shift in the
antinociceptive effects of U50,488H; however, it contrasts
with the Dykstra (1990) study in which butorphanol also
antagonizes the analgesic effects of U50,488H, with the same
potency that it antagonizes the effects of l-methadone. Butorphanol has also antagonized the effects of both mu and
kappa agonists in the in vitro mouse vas deferens assay
(Miller et al., 1986). The contrast in results may reflect differences in species (mouse vs. squirrel monkey) and/or experimental conditions used (thermal antinociception vs. shock
titration vs. in vitro vas deferens assay). Either mu- and/or
kappa-mediated antinociceptive effects of butorphanol could
explain the leftward shifts of the U50,488 dose-effect curve
when combined with low doses of butorphanol. For example,
the data are consistent with butorphanol being an intermediate efficacy mu agonist that potentiates the antinociceptive
effects of U50,488H. Alternatively, these data may reflect a
summation of kappa-mediated antinociceptive effects of both
drugs.
In summary, most of the results presented here suggest
that butorphanol acts as a partial mu agonist in producing its
antinociceptive actions in the mouse radiant-heat tail-flick
test. This evidence comes from pA2 analysis of naltrexone
antagonism data; experiments with selective antagonists for
mu, kappa and delta receptors; and the evaluation of butorphanol as an antagonist of higher-efficacy agonists. Some of
the evidence also suggests that butorphanol has a kappa
component to its analgesic actions in the mouse radiant-heat
tail-flick test: The kappa-selective antagonist nor-BNI antagonized butorphanol analgesia, and combinations of butorpha-
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
ing the range over which the dose-effect curve could be
shifted by naltrexone. This limitation of using U50,488H as
an agonist in the present assay could account for this discrepancy. Because not all dose-effect curves for the naltrexone/U50,488H interaction were parallel, apparent pA2 analysis for this case was considered inappropriate. Analysis of
pKB values, however, indicate that naltrexone was ;10 times
less potent in antagonizing the antinociceptive effect of
U50,488H than of morphine, fentanyl and butorphanol. That
naltrexone produced rightward shifts in the U50,488H doseeffect curve at doses that were ;10 times the doses required
to antagonize the antinociceptive effects of morphine and
fentanyl suggests that U50,488H antinociception was not
due to activity at mu receptors. Previous in vivo and in vitro
studies show that naltrexone is much less potent in antagonizing the effects of U50,488H (Dykstra, 1990; Takemori and
Portoghese, 1984).
Previous studies show that b-FNA is a highly specific for
mu receptors in both in vitro and in vivo assays (Takemori et
al., 1981; Zimmerman et al., 1987). In the present study,
b-FNA produced a dose-related antagonism of the analgesic
activity of butorphanol. Pretreatment with (0.1 mg/kg) of
b-FNA produced a 2.6-fold rightward shift in the dose-effect
curve for butorphanol, although it was not parallel to control.
This dose of b-FNA caused a “flattening” of the dose-effect
curve, decreasing the maximum level of analgesia from
84%MPE to 63%MPE. Theoretically, this lack of parallelism
would be expected for the interaction of full or partial agonists in combination with irreversible or insurmountable antagonists (Ruffolo, 1982). Furthermore, the lack of parallelism of the b-FNA-produced shift in the dose-effect curve of
butorphanol is consistent with a previous study in which
b-FNA antagonized the antinociceptive effects of various
mixed agonist/antagonists, including butorphanol, in the
mouse abdominal stretch test (Zimmerman et al., 1987). Results differ, however, in terms of the magnitude of the shift
produced. This discrepancy can probably be explained by the
much larger pretreatment dose of b-FNA (i.e., 80 mg/kg) that
was used in the previous study, as well as species (rat vs.
mouse) or procedural (abdominal stretch test vs. radiant-heat
tail-flick test) differences. In the report by Zimmerman et al.,
(1987), 80 mg/kg b-FNA produces a 72.4-fold shift in the
butorphanol dose-effect curve. Although the dose-effect curve
generated by pretreatment with 80 mg/kg b-FNA was shifted
in a nonparallel fashion, the antagonism was surmountable.
Limitations imposed by the lethal effects of butorphanol in
the present assay prevented the assessment of higher doses
of butorphanol. The lethal effect was not prevented by a dose
of 10 mg/kg naltrexone. Therefore, in the present study, it is
not clear whether the antagonism of the antinociceptive effects of butorphanol by b-FNA was surmountable. Previously, nor-BNI has been reported to be a specific antagonist
at kappa receptors in in vitro and in vivo studies (Broadbear
et al., 1994; Portoghese et al., 1987). In the present study,
pretreatment with 32 mg/kg nor-BNI failed to antagonize the
analgesic effects of butorphanol; however, there was a significant rightward shift produced by pretreatment with a lower
dose, 10 mg/kg nor-BNI. The reason for this inconsistent
finding is presently unclear, although it suggests that some
components of the analgesic effects of butorphanol are mediated through kappa receptors. Unlike b-FNA, pretreatment
with nor-BNI did not cause a decrease in the maximum level
Butorphanol Antinociception
1260
Garner et al.
Acknowledgments
The authors thank Wen-Lin Sun and Greg Davis for technical
assistance and Dr. Scott Baron for helpful advice in preparation of
the manuscript.
References
ARUNLAKSHANA, O. AND SCHILD, H. O.: Some quantitative uses of drug antagonists. Br. J. Pharmacol. 14: 48–58, 1959.
BERTALMIO, A. J. AND WOODS, J. H.: Differentiation between mu and kappa
receptor-mediated effects in opioid drug discrimination: Apparent pA2 analysis. J. Pharmacol. Exp. Ther. 243: 591–597, 1987.
BOWDLE, T. A., GREICHEN, S. L., BJUSTROM, R. L. AND SCHOENE, R. B.: Butorphanol improves CO2 response and ventilation after fentanyl anesthesia.
Anesth. Analg. 66: 517–522, 1987.
BROADBEAR, J. H., NEGUS, S. S., BUTELMAN, E. R., DECOSTA, B. R. AND WOODS,
J. H.: Differential effects of systemically administered nor-binaltorphimine
(nor-BNI) on k-opioid agonists in the mouse writhing assay. Psychopharmacology 115: 311–319, 1994.
BROWN, G. R.: Stadol dependence: Another case. JAMA 254: 910, 1985.
BUTELMAN, E. R., WINGER, G., ZERNIG, G. AND WOODS, J. H.: Butorphanol:
Characterization of agonist and antagonist effects in rhesus monkeys.
J. Pharmacol. Exp. Ther. 272: 845–853, 1995.
CHEN, J.-C., SMITH, E. R., CAHILL, M., COHEN, R. AND FISHMAN, J. B.: The opioid
receptor binding of dezocine, morphine, fentanyl, butorphanol and nalbuphine. Life Sci. 52: 389–396, 1992.
D’AMOUR, F. E. AND SMITH, D. L.: A method for determining loss of pain
sensation. J Pharmacol. Exp. Ther. 72: 74–79, 1941.
DYKSTRA, L. A.: Behavioral and pharmacological factors in opioid analgesia. In
Behavioral Pharmacology: The Current Status, ed. by L. S. Seiden and R. L.
Balster, pp. 111–129, Alan R. Liss, New York, 1985.
DYKSTRA, L. A.: Butorphanol, levallorphan, nalbuphine and nalorphine as
antagonists in the squirrel monkey. J. Pharmacol. Exp. Ther. 254: 245–252,
1990.
DYKSTRA, L. A., BERTALMIO, A. J. AND WOODS, J. H.: Discriminative and analgesic
effects of mu and kappa opioids: In vivo pA2 analysis. In Transduction
Mechanisms of Drug Stimuli, ed. by F. C. Colpaert and R. L. Balster, pp.
107–121, Springer-Verlag, Berlin, 1988.
DYKSTRA, L. A., GMEREK, D. E., WINGER, G. AND WOODS, J. H.: Kappa opioids in
rhesus monkeys. I. Diuresis, sedation, analgesia and discriminative stimulus effects. J. Pharmacol. Exp. Ther. 242: 413–420, 1987a.
DYKSTRA, L. A., GMEREK, D. E., WINGER, G. AND WOODS, J. H.: Kappa opioids in
rhesus monkeys. II. Analysis of the antagonistic actions of quadazocine and
b-funaltrexamine. J. Pharmacol. Exp. Ther. 242: 421–427, 1987b.
EVANS, W. S., BOWEN, J. N., GIORDANO, F. L. AND CLARK, B.: A case of Stadol
dependence. JAMA 253: 2191–2192, 1985.
FENG, Y. Z., TSENG, Y. T., JAW, S. R., HOSKINS, B. AND HO, I. K.: Tolerance
development to butorphanol: Comparison with morphine. Pharmacol. Biochem. Behav. 49: 649–655, 1994.
HARRIS, R. A.: Interactions between narcotic agonists, partial agonists and
antagonists evaluated by schedule-controlled behavior. J. Pharmacol. Exp.
Ther. 213: 497–503, 1980.
HORAN, P., DECOSTA, B. R., RICE, K. C. AND PORRECA, F.: Differential antagonism
of U69,593- and bremazocine-induced antinociception by (2)-UPHIT: Evidence for kappa opioid receptor multiplicity in mice. J. Pharmacol. Exp.
Ther. 257: 1154–1161, 1991.
HORAN, P. J. AND HO, I. K.: Comparative pharmacological and biochemical
studies between butorphanol and morphine. Pharmacol. Biochem. Behav.
34: 847–854, 1989.
HORAN, P. J. AND HO, I. K.: The physical dependence liability of butorphanol: A
comparative study with morphine. Eur. J. Pharmacol. 203: 387–391, 1991.
HOUDE, R. W.: Analgesic effectiveness of the narcotic agonist-antagonists.
Br. J. Clin. Pharmacol. 7: 297S–308S, 1979.
KENAKIN, T. P.: Pharmacologic Analysis of Drug-Receptor Interaction, Raven
Press, New York, 1987.
LAWHORN, C. D. AND BROWN, R. E., JR.: Epidural morphine with butorphanol in
pediatric patients. J. Clin. Anesth. 6: 91–94, 1994.
LAWHORN, C. D., MCNITT, J. D., FIBUCH, E. E., JOYCE, J. T. AND LEADLEY, R. J.,
JR.: Epidural morphine with butorphanol for postoperative analgesia after
cesarean delivery. Anesth. Analges. 72: 53–57, 1991.
LEANDER, J. D.: Evidence that nalorphine, butorphanol and oxilorphan are
partial agonists at a k-opioid receptor. Eur. J. Pharmacol. 86: 467–470,
1983a.
LEANDER, J. D.: A kappa opioid effect: Increased urination in the rat. J. Pharmacol. Exp. Ther. 224: 89–94, 1983b.
MILLER, L., SHAW, J. S. AND WHITING, E. M.: The contribution of intrinsic activity
to the action of opioids in vitro. Br. J. Pharmacol. 87: 595–601, 1986.
MORGAN, D. AND PICKER, M.: Contribution of individual differences to discriminative stimulus, antinociceptive, and rate decreasing effects of opioids:
Importance of the drugs intrinsic efficacy at the mu receptor. Behav. Pharmacol. 7: 261–275, 1996.
NEGUS, S. S., BURKE, T. F., MEDZIHRADSKY, F. AND WOODS, J. H.: Effects of opioid
agonists selective for mu, kappa and delta opioid receptors on schedulecontrolled responding in rhesus monkeys: Antagonism by quadazocine.
J. Pharmacol. Exp. Ther. 267: 896–903, 1993.
O’CALLAGHAN, J. P. AND HOLTZMAN, S. G.: Quantification of the analgesic activity
of narcotic antagonists by a modified hot-plate procedure. J. Pharmacol.
Exp. Ther. 192: 497–505, 1975.
PICKER, M. J., NEGUS, S. S. AND CRAFT, R. M.: Butorphanol’s efficacy at mu and
kappa opioid receptors: Inferences based on schedule-controlled behavior of
nontolerant and morphine-tolerant rats and on the responding of rats under
a drug discrimination procedure. Pharmacol. Biochem. Behav. 36: 563–568,
1990.
PITTS, R. C., WEST, J. P., MORGAN, D., DYKSTRA, L. A. AND PICKER, M. J.: Opioids
and rate of positively reinforced behavior: Differential antagonism by naltrexone. Behav. Pharmacol. 7: 205–215, 1996.
PORRECA, F., MOSBERG, H. I., HURST, R., HRUBY, V. J. AND BURKS, T. F.: Roles of
mu, delta and kappa opioid receptors in spinal and supraspinal mediation of
gastrointestinal transit effects and hot-plate analgesia in the mouse.
J. Pharmacol. Exp. Ther. 230: 341–348, 1984.
PORTOGHESE, P. S., LIPKOWSKI, A. W. AND TAKEMORI, A. E.: Binaltorphimine and
nor-binaltorphimine: Potent and selective k-opioid receptor antagonists. Life
Sci. 40: 1287–1292, 1987.
PORTOGHESE, P. S., SULTANA, M. AND TAKEMORI, A. E.: Naltrindole, a highly
selective and potent non-peptide d-opioid receptor antagonist. Eur. J. Pharmacol. 146: 185–186, 1988.
PRESTON, K. L. AND BIGELOW, G. E.: Drug discrimination assessment of agonistantagonist opioids in humans: A three-choice saline-hydromorphonebutorphanol procedure. J. Pharmacol. Exp. Ther. 271: 48–60, 1994.
RUFFOLO, R. R.: Important concepts of receptor theory. J. Auton. Pharmacol. 2:
277–295, 1982.
SHANNON, H. E., CONE, E. J. AND GORODETZKY, C. W.: Morphine-like discriminative stimulus effects of buprenorphine and demethoxybuprenorphine in
rats: Quantitative antagonism by naloxone. J. Pharmacol. Exp. Ther. 229:
768–774, 1986.
SHYU, W. C., PITTMAN, K. A., ROBINSON, D. AND BARBHAIYA, R. H.: Multiple-dose
phase I study of transnasal butorphanol. Clin. Pharmacol. Ther. 54: 34–41,
1993.
SMITH, M. A. AND PICKER, M. J.: Examination of the kappa agonist and antagonist properties of opioids in the rat drug discrimination procedure: Influence of training dose and intrinsic efficacy. Behav. Pharmacol. 6: 703–717,
1995.
SMITH, S. G. AND DAVIS, W. M.: Nonmedical use of butorphanol and diphenhydramine. JAMA 252: 1010, 1984.
SOFUOGLU, M., PORTOGHESE, P. S. AND TAKEMORI, A. E.: Differential antagonism
of delta opioid agonists by naltrindole and its benzofuran analog (NTB) in
mice: Evidence for delta opioid receptor subtypes. J. Pharmacol. Exp. Ther.
257: 676–680, 1991.
SPANAGEL, R., ALMEIDA, O. F. X. AND SHIPPENBERG, T. S.: Evidence that norbinaltorphimine can function as an antagonist at multiple opioid receptor
subtypes. Eur. J. Pharmacol. 264: 157–162, 1994.
TAKEMORI, A. E.: Determination of pharmacological constants: Use of narcotic
antagonists to characterize analgesic receptors. In Narcotic Antagonists, ed.
by M. C. Braude, L. S. Harris, E. L. May, J. P. Smith and J. E. Villarreal,
Advances in Biochemical Psychopharmacology, Vol. 8, pp. 335–344, Raven
Press, New York, 1974.
TAKEMORI, A. E., LARSON, D. L. AND PORTOGHESE, P. S.: The irreversible narcotic
antagonistic and reversible agonistic properties of the fumaramate methyl
ester derivative of naltrexone. Eur. J. Pharmacol. 70: 445–451, 1981.
TAKEMORI, A. E. AND PORTOGHESE, P. S.: Comparative antagonism by naltrexone
and naloxone of m, k, and d agonists. Eur. J. Pharmacol. 104: 101–104, 1984.
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017
nol with U50,488H produces greater antinociception than
U50,488H alone, suggesting a coagonist action. That butorphanol may have kappa activity in this assay was not surprising given that numerous studies (some of which are reviewed herein) have reported a kappa component to the
actions of butorphanol. What was surprising was that the
data supporting a kappa-antinociceptive effect is somewhat
equivocal. In the selective antagonist study, the antagonism
of butorphanol analgesia by nor-BNI was not dose dependent. Furthermore, one could interpret the coagonist effects
of butorphanol in combination with U50,488H as the summed
actions of a mu (butorphanol) and kappa (U50,488H) agonist.
However, a common theme throughout the butorphanol literature is that results often seem to depend on species and
the particular effect being measured. Taken together, the
results of the present study suggest that butorphanol acts as
a partial agonist in the mouse radiant-heat tail-flick test and
that activity at mu receptors accounts for the majority of its
antinociceptive effects.
Vol. 282
1997
TALBERT, R. L., PETERS, J. I., SORRELS, S. C. AND SIMMONS, R. S.: Respiratory
effects of high-dose butorphanol. Acute Care 12: (suppl. 1) 47–56, 1988.
TALLARIDA, R. J., COWAN, A. AND ADLER, M. W.: pA2 and receptor differentiation:
A statistical analysis of competitive antagonism. Life Sci. 25: 637–654, 1979.
TALLARIDA, R. J. AND MURRAY, R. B.: Manual of Pharmacologic Calculations with
Computer Programs, 2nd ed., Springer-Verlag, New York, 1987.
UPTON, N., SEWELL, R. D. E. AND SPENCER, P. S. J.: Differentiation of potent mand k-opiate agonists using heat and pressure antinociceptive profiles and
combined potency analysis. Eur. J. Pharmacol. 78: 421–429, 1982.
VOGELSANG, J. AND HAYES, S. R.: Butorphanol tartrate (Stadol): A review. J. Post
Anesth. Nursing 6: 129–135, 1991.
WALKER, E. A., MAKHAY, M. M., HOUSE, J. D. AND YOUNG, A. M.: In vivo apparent
pA2 analysis for naltrexone antagonism of discriminative stimulus and
analgesic effects of opiate agonists in rats. J. Pharmacol. Exp. Ther. 271:
959–968, 1994.
WARD, S. J., PORTOGHESE, P. S. AND TAKEMORI, A. E.: Pharmacological characterization in vivo of the novel opiate, b-funaltrexamine. J. Pharmacol. Exp.
Ther. 220: 494–498, 1982.
WARD, S. J. AND TAKEMORI, A. E.: Relative involvement of mu, kappa and delta
Butorphanol Antinociception
1261
receptor mechanisms in opiate-mediated antinociception in mice. J. Pharmacol. Exp. Ther. 224: 525–530, 1983.
WESSINGER, W. D. AND MCMILLAN, D. E.: Quantitative analysis of naloxone
antagonism of the discriminative stimulus properties of morphine in the
pigeon. Pharmacol. Biochem. Behav. 25: 209–214, 1986.
YOUNG, A. M., MASAKI, M. A. AND GEULA, C.: Discriminative stimulus effects of
morphine: Effects of training dose on agonist and antagonist effects of mu
opioids. J. Pharmacol. Exp. Ther. 261: 246–257, 1992.
ZIMMERMAN, D. M., LEANDER, J. D., REEL, J. K. AND HYNES, M. D.: Use of
b-funaltrexamine to determine mu opioid receptor involvement in the analgesic activity of various opioid ligands. J. Pharmacol. Exp. Ther. 241: 374–
378, 1987.
Send reprint requests to: Dr. William D. Wessinger, University of Arkansas
for Medical Sciences, Department of Pharmacology and Toxicology, Slot 611,
4301 W. Markham Street, Little Rock, AR 72205. E-mail: wdwessinger@
life.uams.edu
Downloaded from jpet.aspetjournals.org at ASPET Journals on June 16, 2017