Download Regulation of the Cardiovascular System in Crayfish12 The

AMER. ZOOL., 35:37^»8 (1995)
Regulation of the Cardiovascular System in Crayfish12
JERREL L. WILKENS
Department of Biological Sciences, University of Calgary, Calgary, Alberta T2N 1N4, Canada
INTRODUCTION
The integrated function of the cardiovascular system of a crayfish is required in order
to meet the circulatory requirements of the
animal. These requirements are likely to
change over time and in different situations.
The cardiovascular system is made up of a
neurogenic heart which pumps blood into
an open vascular system made of musclefree arteries. The arteries branch into finer
arterioles which in turn discharge into capillary-like lacunae. Blood is collected into a
number of sinuses (Greenaway and Farrelly,
1984) and returns to the heart via a series
of channel-like extensions of these sinuses.
A brief survey of some of the cardiovascular
adjustments which have been identified in
whole animal studies is presented first to
anticipate some of the control points which
are important in this system. The mechanisms by which adjustments occur will form
the main focus of this paper. Most of the
data presented here is derived from studies
on crayfish, but those derived from other
decapods will also be presented where comparable information is lacking for crayfish.
WHOLE ANIMAL OBSERVATIONS
At the level of the heart, beat rate (fH),
stroke volume (Vs) and cardiac output (0)
have received the most attention. Rate is
easy to monitor with AC amplifiers and
impedence converters while Q has been calculated from applications of the Fick Equation or by a thermodilution technique (Burnett et al., 1981). Stroke volume is obtained
as the quotient of Q divided by fH.
1
From the Symposium Physiology and Adaptations
in Crayfish presented at the Annual Meeting of the
American Society of Zoologists, 26-30 December 1993,
at Los Angeles, California.
2
Abbreviations: CA, cardioaccelerator nerves;
CCAP, crustacean cardioactive pcptide; CI, cardioinhibitor nerves; DA, dopamine; FaRPs, FLRFamiderelated peptides; fH> heart rate; OA, octopamine; Q»
cardiac output; PRO, proctolin; 5-HT, serotonin or
5-hydroxytryptamine; V,, stroke volume.
37
Rapid changes in fH, including cardiac
arrest, occur in response to a variety of
external stimuli including the startle
response (Larimer and Tindel, 1966; Wilkens, 1987). During forced exercise both fH
and 0 a r e increased in most cases (Cancer
magister [McMahon et ai, 1979], Carcinus
maenas [Houlihan et al., 1984; Hamilton
and Houlihan, 1992], fH but not Q in Callinectes sapidus [Booth et al., 1982]). Stroke
volume increased in a number of cases
(McMahon et al., 1979; Depledge, 1978)
but decreased in others (Booth et al., 1982).
In response to hypoxia, two species of crayfish were able to maintain or increase Q m
the face of bradycardia by increasing Vs
(Orconectes rusticus [Wilkes and McMahon, 1982], Procambarus clarkii [Reiber et
al., 1992]). Thus, there is evidence that crustaceans have the ability to independently
regulate fH and Vs.
The distribution of blood to the seven
arteries (nomenclature in McLaughlin, 1983)
which leave the single chambered heart can
also be controlled. By employing a noninvasive pulsed-Doppler flowmeter technique, changes in the flow profile among
these arteries have been observed in crayfish, crabs and lobsters during hypoxia and
in response to neurohormones (Reiber et
al., 1992; Airriess and McMahon, 1992;
McMahon, 1992; Reiber, 1995). Recent
reports confirm that different profiles of distribution do occur in different situations,
e.g., rest, locomotion and hypoxia (Airriess
and McMahon, 1994; McGaw et al., 1995).
OBSERVATIONS FROM ISOLATED
SYSTEMS
In order to identify and characterize the
mechanisms available and/or used in cardiovascular regulation I will take the reductionist approach of describing research based
on isolated parts of the system. All of the
figures presented in this paper are of unpublished data.
38
JERREL L. WILKENS
Wilkens and McMahon, 1994). As outflow
resistance is increased, ventricular pressure
increases but only to the level produced
40
when all outflow is prevented. V5 decreases
eventually to zero while fH is unaltered. In
myogenic molluscan (Smith, 1987) and ver20 <0
50 100 150 ZOO 250
tebrate (Berne and Levy, 1992) hearts
venous return of blood preloads the heart
1.2
30 during diastole. The heart compensates for
increases in preload by increasing Vs and
sometimes also by increasing fH. There is
15
c
no venous return to crayfish hearts, but
rather theyfillfrom the pericardial sinus via
E
ostia. The end-diastolic volume of the deca0.0
50 100 150 200 250
0
pod ventricle is determined by the amount
of elastic recoil of the alary and suspensory
ligaments. Thus, the stretch imposed by the
^
1.2
ligaments may be viewed as imparting an
o
0_
external form of preload. It is not known
•^
0.B
whether these external suspensory systems
c
o
are able to adjust end-distolic volume, but
a." 0.4
in crayfish the pericardial septum which is
0
50 100 150 200 250
attached to the ventral wall of the heart by
numerous connective tissue strands is
Outflow resistance (Pa/ml.min )
invested with muscle bands and appears to
FIG. 1. In situ Procambarus clarkii hearts respond expand the ventral wall of the heart during
passively to increases in outflow resistance. Heart rate, diastole (George et al., 1955). In C. magister
as determined by the burst rate of the cardiac ganglion, the origins of the alary ligaments contain
is unaffected; stroke volume decreases as resistance
increases and the ventricular systolic pressure increases slips of striated muscle (Volk, 1988). The
toward the level which occurs during isovolumic con- effects on cardiac output of altering the tentractions when all outflow is prevented. Mean ± SEM, sion in either of these ligamentous systems
n = 5 (Wilkens and Walker, unpublished).
is not known. Artificially increasing preload
by direct heart perfusion in crayfish does
stretch the heart wall and does cause
Semi-isolated heart
increases in systolic pressure and Vs, but
Crayfish hearts are neurogenic in that the heart rate is either unaffected or slowed
basic heart beat and rhythm are determined (Wilkens, 1993). It must be emphasized that
by the nervous output of the cardiac gan- this direct form of preload will never occur
glion which is located on the inner dorsal in an intact animal. Since no automatic
wall of the heart (Alexandrowicz, 1932). The compensatory mechanisms are known, we
myocardium itself is not spontaneously must look for control mechanisms external
active. Semi-isolated hearts, "on the half to the heart for the causes of changes in fH
shell," suspended by their suspensory liga- and Vs.
ments, beat and pump fluid with a strong
and regular rhythm for hours (Wilkens and
The extrinsic control of fH can arise from
Walker, 1992; Wilkens and Mercier, 1993). the cardioregulatory nervous and neuroThe proximal portions of all arteries and all hormonal inputs. The factors which could
extrinsic innervation to the heart remain account for the changes in Vs in intact aniintact and each is accessible for manipula- mals are not known, but candidates include
tion.
(i) changes in end-distolic volume resulting
/. Lack of autoregulation. —Isolated from dynamic changes in alary ligament
hearts do not show compensatory responses tension (unstudied), (ii) changes in systolic
to increases in arterial afterload or to ejection fraction which might accompany
increases in peripheral resistance (Fig. 1, also neurohormone induced increases in con60
39
CARDIOVASCULAR REGULATION
70
120
r
r
(bpm
60
50
<u
40 L L
o
100
80
3
Heart
cr
50
IALJ.
2
7
x/'
° Ligament loss
• Oenervotion
en
-*l
40
i
V
1
o Control
60
c
T
-4
30
'E
E
20
0
10
20
30
40
10
20
30
40
1.0
0.8
0.6
0.4
Stimulating frequency (Hz)
FIG. 2. The cardioacceleratory nerves exert only
chronotropic effects on heart performance. The increases
in cardiac output of in situ Procambarus clarkii hearts
results from the increased fH, while ventricular systolic
pressure and stroke volume remain relatively constant
over the same range of stimulating frequencies. Experiments performed at 18°C in crayfish saline. Mean ±
SEM, n = 5 (Wilkens and Walker, unpublished).
40
-10
10
20
30
40
Time (min)
FIG. 3. Effects of treadmill locomotion on heart rate
in control Homarus americanus, and after first reducing cardiac output by severing the two dorso-anterior
alary ligaments and then after severing the two dorsal
nerves. Following each surgical procedure the lobsters
were allowed 24 hr to recover before being tested again.
The sea water in the underwater treadmill was continuously exchanged with the holding aquarium and was
maintained at 12°C. Mean ± SEM, error bars for controls not shown, but they do not overlap those of the
other traces except at the end of the 30 min period.
Treadmill speed was 1.7 m • min -' (Guirguis and Wilkens, 1995).
frequency of the inhibitors above 12 Hz
causes cardiac arrest and there is strong reciprocity between activity in the accelerators
and the inhibitors. We have recently been
examining the effects of regulatory nerve
input on the pumping performance of isotractility (Pvent, see below) and/or (iii) chan- lated hearts (Wilkens and Walker, 1992).
ges in total peripheral resistance (see below). During CA stimulation fH and Q increase,
2. Nervous control.—The cardioregula- but Vs and PvenI do not change (Fig. 2). Durtory innervation of the heart consists of a ing CI stimulation heart rate decreases linpair of bilateral dorsal nerves, each of which early with increasing frequency of stimucarries two cardioaccelerator (CA) and one lation, but Vs falls only at stimulation rates
inhibitor (CI) axons. These nerves arise from above 10 Hz (data not shown). Thus, the
the subesophageal ganglion (Wiersma and regulatory nerves provide an effective means
Novitski, 1942; Maynard, 1953; Florey, of making rapid adjustments in fH and Q,
1960; Field and Larimer, 1975). The CIs while the increases in Vs, as observed in
synapse only on the cardiac ganglion, while intact animals, probably do not arise from
the CAs may synapse on both the cardiac the effects of cardioregulatory nervous
ganglion and sometimes directly on the inputs.
myocardium as well (Maynard, 1960;
The importance of the cardioregulatory
Yazawa and Kuwasawa, 1984). In situ, both nerves on the overall control of fH is illusaxon types exhibit a low background level trated by the responses of lobsters {Homaof spike activity which is punctuated by high rus americanus) during treadmill locomofrequency bursts of spikes (Field and Lari- tion (Fig. 3). In controls, fH increases from
mer, 1975; Young, 1978). Increases in the rest rates to a plateau in the first two minutes
40
JERREL L. WILKENS
100 r Procambarus
80
60
40
20
o
DA
5-HT
OA
c
O
a.
50
PR
OF,
CCAP
f Homarus
40
30
20
10
<o
DA
5-HT
OA
PR
CCAP
PR
5-HT
CCAP
FIG. 4. Comparisons of the effects of pericardial organ
neurohormones on heart rate, expressed as percent
change from control, in three different decapod crustaceans. The semi-isolated hearts were continuously
perfused at 1 ml • min~', 2 ml • min~' in Homarus, with
an appropriate saline. Each neurohormone was applied
for 30 sec by switching the perfusion pump supply from
control saline to saline containing the appropriate compound. Procambarus: All compounds except DF2 were
tested at 0.1 /tin, DF2 was tested at 10 nm (Guirguis
and Wilkens, unpublished). Homarus (Kuramoto,
Wilkens, and McMahon, unpublished) and Carcinus
(Saver and Wilkens, unpublished): DA, OA and 5-HT
were tested at 10 nm, the peptides were tested at 10
nm. Mean ± SEM, n = 3-9.
after the onset of walking and is maintained
at relatively constant levels for the duration
of a 30 minute walk. After the cardiac output is reduced by about 25 percent by cutting two of the alary ligaments (Wilkens and
McMahon, 1992), fH is elevated both at rest
and during locomotion. It seems clear that
the animals sense the cardiac insufficiency
and compensate by increasing fH. Next, after
bilateral dorsal nerve section, resting fH is
reduced to the level shown by controls. The
reduced resting rates, relative to those during the immediately preceding period when
the ligaments were cut, may arise from the
removal of tonic CA drive. During walking
following combined alary ligament and
nerve section, heart rate does increase slowly
over about 25 minutes, but does not reach
the previous levels seen after ligament cutting. The stimuli responsible for this gradual
onset oftachycardia are not known, but they
may include neurohormones. Despite this
slow increase in heart rate, walking endurance is severely impaired in these animals.
3. Neurohormonal control.—The crayfish heart is quite responsive to the neurohormones known to be released from the
pericardial organs and one similar to a peptide found in the hindgut nerve plexes. The
actions of most of these hormones are compared on the semi-isolated hearts of crayfish
(P. clarkii), crabs (C. maenas) and lobsters
(Homarus americanus) in Figure 4.
The pericardial organ aminergic neurohormones are 5-hydroxytryptamine (5-HT,
serotonin), dopamine (DA) and octopamine
(OA) (Cooke and Sullivan, 1982). In the
three genera illustrated in Figure 4, 5-HT
consistently produced the greatest effect,
while DA and OA were less potent. In two
other species of crayfish 5-HT, DA and OA
each caused increases in the frequency and
amplitude of the heart beat (Astacus leptodactylus and Eriphia spinifrons [Florey and
Rathmayer, 1978]).
All of the pericardial organ peptide neurohormones, crustacean cardioactive peptide (CCAP [Strangier et ai, 1987]), proctolin (PR [Sullivan, 1979]) and several
FLRFamide-related peptides (FaRPs, references follow), caused fH to increase (Fig.
4), but see Figure 8 for exceptions. There is
some species specificity in the responsiveness to some of these hormones. Crustacean
cardioactive peptide produces moderate to
strong positive chronotropic and inotropic
effects on Orconectes limosus (Strangier and
Keller, 1992), P. clarkii and C. maenas
(Wilkens and McMahon, 1992; Wilkens and
Mercier, 1993). Lobster hearts and those of
another crab, C. magister (data for latter not
shown) are unresponsive to CCAP. All of
41
CARDIOVASCULAR REGULATION
these peptides, except proctolin, cause parallel increase in beat rate and contractility.
In all three genera proctolin is weakly
chronotropic but strongly inotropic, an
indication that this peptide is effective both
at the level of the cardiac ganglion (rate
effects) and on the myocardium (force
effects) (Wilkens and Mercier, 1993, for force
data).
A number of FMRFamide-related peptides (FaRPs) have been identified in the
pericardial organs of crayfish (DF2, DRNFLRFamide and NF1, NRNFLRFamide
[Mercier et al., 1993]) and lobsters (Fl,
TNRNFLRFamide and F2, SDRNFLRFamide [Trimmer et al., 1987]). In P. clarkii
hearts, Fl and F2 increased both heart rate
and contraction amplitude (Mercier et al.,
1991; Mercier and Russenes, 1992) whereas
two FaRPs of insect origin with significantly
different amino-terminal extensions (leucomyosuppression, pQDVDHVFLRFamide
[Holman et al., 1986], and SchistoFLRFamide, PDVDHVFLRFamide [Robb et al.,
1989]) strongly inhibit heart rate while
increasing the amplitude of contraction (Fig.
5; also Mercier and Russenes, 1992). The
low threshold for the inhibitory peptide
SchistoFLRFamide (1 nm) suggested to
Mercier that crayfish hearts possess receptors for this or a closely related peptide.
A peptide from the crayfish hindgut nerve
plexus is identical to locust SchistoFLRFamide at the first six C-terminal residues (Mercier, TeBrugge and Orchard, personal communication). Guirguis and
Wilkens found that the inhibitory effects of
this peptide on crayfish hearts were long
lasting and generally irreversible when tested
at l/xm.
When the effects of six members of the
FaRP family (Fl, F2, DF2, NF1, FLRFamide and FMRFamide) are compared on isolated P. clarkii hearts, the native peptides
(DF2 and NF1) are found to be more stimulatory than the lobster peptides (Fl and
F2) or the root peptides FLRFamide or
FMRFamide (Price and Greenberg, 1977)
(Figs. 6, 7). In 3 of 5 hearts, the lowest concentrations of DF2 (Fig. 8), NF1, FLRFand FMRFamide caused biphasic responses,
bradycardia and depressed systolic pres-
Rate
Pressure
o
-11
-10
-9
-8
log [F21
100n
Rate
Pressure
60
a
o>
S
5
20
-20
-60-100
-9
-8
-7
log [Schisto]
FIG. 5. Concentration-response relationships comparing the chronotropic and inotropic effects of the
peptides F2 and SchistoFLRFamide on semi isolated
Procambarus clarkii hearts. Plotted are the relative
changes in heart rate after 1 min and arterial pressure
after 3 min during a 5 min period of perfusion with
the neurohormone. These observations were made
during June, 1990, mean ± SEM, n = 3-8 at each
concentration (Mercier and Wilkens, unpublished).
sure, followed by tachycardia and increased
systolic pressure, while high concentrations
only caused tachycardia and increased pressure. On the other two hearts all concentrations caused dose-dependent increases in all
parameters; however, on one of these hearts
a 0.01 nm challenge produced inhibition
similar to that shown for 0.1 nm in Figure
6. It appears as if the heart may contain high
affinity receptors which cause bradycardia
and low affinity ones responsible for tachycardia. The threshold for bradycardia may
vary from animal to animal. The inhibitory
effects of Fl and F2 were not reported in
the study by Mercier and Russenes (1992).
Vascular system
1. Cardioarterial valves.— Some of the
changes in blood distribution in intact animals documented by the pulsed-Doppler
technique may be controlled by the semi-
42
JERREL L. WILKENS
200
NF1
150
100
c
(D
O
-t->
50
0
200
200
150
150
100
100
50
50
0
0
F2
O
-M
O
200
CD
200
cn
c
o
150
150
100
100
50
50
0
0
o
FMRF
FLRF
Concentration (M)
FIG. 6. Comparison of the relative chronotropic effects of FaRPs (FMRFamide-related peptides) on in situ
Procambarus clarkii hearts. Each of the 5 hearts tested was exposed to all three concentrations of each of the
six peptides. The six peptides were first applied at the lowest concentration, then each at the intermediate and
finally at the highest concentration; however, the order of presentation among the six was randomized. Each
compound was applied at the rate of 1 ml-min-' for 30 sec during continuous perfusion. In three hearts the
lower concentrations caused biphasic responses, bradycardia followed by tachycardia. Only the acceleratory
responses are plotted here. These data were collected September to December, 1993. Mean ± SEM, n = 5
(Guirguis and Wilkens, unpublished).
lunar cardioarterial flap valves located at
the origin of each artery at the heart. The
valves in crayfish, crabs and lobsters are
invested with muscle and are innervated
(Alexandrowicz, 1932). In isopods and lobsters they receive excitatory and/or inhibitory innervation (Kihara etai, 1985; Kuramoto et al., 1992). Contraction of valve
muscles will stiffen the valve and decrease
blood flow through it, while inhibitory input
will relax the muscles and allow increased
blood flow (Kuramoto and Ebara, 1989;
Fujiwara-Tsukamoto et al, 1992). These
valves can thus serve the dual functions of
passively preventing back flow of blood
during diastole and of actively regulating
the distribution of blood among the various
arteries. The effect of such control is illustrated in the isopod, Bathynomus doederleini, where inhibitory nerve input to the
5th lateral artery valves which control blood
supply to the swimmerettes coincides with
activation of the swimmerettes (FujiwaraTsukamoto et al, 1992).
43
CARDIOVASCULAR REGULATION
NF1
c
CD
O
l_
CD
Q_
F2
CD
i_
CO
CO
CD
L_
Q.
c
CD
CT>
FMRF
C
O
.r:
O
20
10
Concentration (M)
FIG. 7. Comparison of the relative inotropic effects of six FaRPs on in situ Procambrus clarkii hearts. These
data were collected from the same hearts as those shown in Figure 6.
In Panulirns japonicus the cardioarterial
valves are also excited or inhibited by different cardioactive neurohormones (Kuramoto and Ebara, 1984). Proctolin causes
depolarization of the anterior and posterior
cardioarterial valves, 5-HT causes hyperpolarization and relaxation of the same
valves as well as increases in heart rate, while
OA causes contraction of the posterior valve
and relaxation of the anterior valve. Thus,
each neurohormone should produce a different blood flow distribution pattern. In H.
americantis proctolin, 5-HT and F2 cause
the sternal arterial valve to contract while
dopamine relaxes it (Kuramoto et al, 1992;
Kuramoto, Wilkens, and McMahon, 1995).
Neurohormones may be important in con-
trolling arterial valve tonus, while the nervous control could function over shorter
time periods.
Crayfish cardioarterial valves have not
been studied, but it is anticipated that individual valves will also show differential
responsiveness to innervation and to neurohormones. The nervous and neurohormonal control of the cardioarterial valves
may be one mechanism of controlling blood
distribution.
2. Arteries.—In general, arteries do not
contain muscle layers and it has been
assumed that they only serve as passive conduits for blood distribution; however, recent
evidence shows that they are not passive.
In crayfish muscular flap valves are located
44
JERREL L. WILKENS
DF
2
10
10
mol L
8
mol L
12
-6
10
-1
mol L
2 min
o
FIG. 8. Records, typical of 3 of 5 preparations, showing the effects of 30 sec exposures of a perfused Procambarus
clarkii heart to three concentrations of the peptide DF2. At 0.1 nm the peptide reduced fH, Pvent and Q, at 10
nm the early inhibitory phase was followed by acceleration and increased contractility, while at 1 nm the peptide
caused increases in all three parameters. The non-linear response characteristics of the flow transducer mask to
fact that flow increased almost 2-fold during 1 nm DF2 exposure. Note that the increases in fH occur more
rapidly than the increases in Pvcm (Guirguis and Wilkens, unpublished).
at the origin of the two primary lateral arteries from the dorsal abdominal artery in each
abdominal segment and at the bifurcation
in the 5th segment. These valve muscles are
I
12
'E
10
sensitive to a variety of neural transmitters
and neurohormones (Fig. 9). Valve contractions induced by a 60 sec exposure to
acetylcholine, and a 30 sec exposure to proctolin and 5-HT relax slowly over about five
minutes, whereas it requires more than an
hour of washing after a similar 30 sec exposure to Fl or F2 before relaxation begins.
These lateral arterial valves are also innervated (Alexandrowicz, 1913) and their
physiology is currently under investigation.
o
CONTROL OF BLOOD PRESSURE AND OF
" L U N G " PERFUSION
c
o
-100
100
200
Time
(s)
300
400
FIG. 9. The magnitude and time course of response
to four neurohormones (5-HT, proctolin, Fl and F2,
30 sec exposure each) and acetylcholine (60 sec exposure) on the resistance of a Procambarus clarkii dorsal
abdominal artery during continuous perfusion at 1 mlmin-'. Each compound was presented at 10 nm. To
measure the resistance to flow, the artery was cannulated and perfused via a peristaltic pump. The resistance is the quotient of the back pressure generated in
the cannula divided by the flow rate (Lovell and Wilkens, unpublished).
There is no evidence in any crustacean
that the heart or vascular system is involved
in the regulation of overall blood pressure.
However, in crabs, arrays of dorsoventral
muscles span the coelomic space between
the dorsal carapace and the flexible anterior
lining of the branchial chambers. Contraction or relaxation of these muscles accompanies decreases or increases in blood volume, respectively, and helps restore blood
pressure to control levels after such perturbations (C maenas [Rajashekhar and Wilkens, 1991; Taylor and Taylor, 1991; Taylor
et ai, 1992], Goniopsis cruentata [Wilkens
and Young, 1992]). Contraction of these
45
CARDIOVASCULAR REGULATION
3 x 10-7 M F 2
3 x 10-7 M
J
FIG. 10. Effects of bath application of two FaRPs on Prcocambarus clarkii hindguts. Each peptide caused an
increase in the amplitude of the spontaneous rhythmic contractions of these tissues. The upward deflections
represent longitudinal contractions. The decrease in baseline during portions of both traces represent lengthening
of the gut strip, probably are a consequence of contractions of the circular muscle layers. Calibrations: verticle
= 0.5 nm, horizontal = 2 min (Schmoeckel and Mercier, unpublished).
muscles, acting as an auxiliary pump, also
facilitates perfusion of the branchiostegal or
lung lacunar network. (Wilkens and Young,
1992). It is not known whether crayfish possess homologous dorsoventral muscles;
however, perfusion of the branchiostegal
lungs may be important to crayfish during
air exposure, as when burrowing or migrating over land. A search for such a control
system might be fruitful.
the act of ingesting food triggers a release of
peptides which will facilitate the movement
of that food through the gut.
Recall also that the FaRPs can increase
fH and ventricular pressure. The resulting
increased blood flow may be directed toward
organs associated with digestive processes.
The cardioarterial flap valve at the origin
of the dorsal abdominal artery in H. americanus and P. clarkii does not contain muscle and is unresponsive to the FaRPs
AN EMERGING STORY OF NEUROHORMONAL (Kuramoto, Wilkens, and McMahon, 1995)
INTEGRATION—THE ROLE OF F A R P S IN
so that there should be no regulation of
DIGESTIVE AND CIRCULATORY
blood entry into this large vessel. However,
PROCESSES
the FaRPs cause powerful and prolonged
In P. clarkii the circulating level of closure of the lateral arterial valves which
FaRPs is substantially elevated following branch off of the dorsal abdominal artery
feeding. FMRFamide-like immunoreac- and contraction of these valves reduces
tivity increased 300% one hour after feed- blood flow to the abdominal musculature
ing (from 0.16 ± 0.02 nm to 0.63 ± 0.13 and the swimmerettes and causes the presnm, n = 8; Mercier, personal communi- sure in the dorsal abdominal artery to rise.
cation). Similar blood levels of FaRPs are A large number of small diameter arteries
reported in lobsters, but these levels were branch off of the ventral wall of the dorsal
not related to any physiological or behav- abdominal artery to supply blood to the
ioral state (Kobierski et al., 1987). FaRPs intestine. The origins of these arteries are
also induce strong pyloric and gastric mill not controlled by valves and the FaRPrhythms in the Cancer irroratus and Cancer induced increases in arterial pressure should
borealis stomatogastric ganglion (Hooper increase flow of blood to the gut.
and Marder, 1984; Weiman et al, 1990)
The picture which is emerging is that the
and increase motility of isolated crayfish FaRPs released during feeding may help
hindgut (Fig. 10). Thus, it would appear that control several systems whose integrated
46
JERREL L. WILKENS
functions will aid the processing, digestion
and absorption of food.
SUMMARY
All levels of the cardiovascular system,
from the heart to the cardioarterial valves
and the dorsal abdominal arterial valves,
receive nervous input and all are responsive
to neurohormones. The sites of action of
neurohormones on the other arteries are not
known at present. The challenge for the
future is to devise experiments which will
allow us to measure which of these control
systems are operative to produce the patterns of heart and vascular performance
observed in intact animals.
ACKNOWLEDGMENTS
To participate in this symposium has special significance to me since Milton Fingerman, a co-organizer of the symposium, was
my first graduate supervisor at Tulane University 32 years ago. I wish to thank him
for being my first real scientific mentor. I
also thank Dr. A. J. Mercier for sharing
unpublished data and for reviewing the
manuscript, and Dr. I. Orchard for samples
of the peptides DF2 and NF1. Supported
by grants from the National Science and
Engineering Research Council, Canada.
REFERENCES
Airriess, C. N. and B. R. McMahon. 1992. Aminergic
modulation of circulatory performance in the crab,
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