Download Glucose Metabolism and the Percentage of

[CANCER
RESEARCH
42, 4936-4942,
December 1982]
Glucose Metabolism and the Percentage of Glucose Derived from Alanine:
Response to Exogenous Glucose Infusion in Tumor-bearing and NonTumor-bearing Rats
Jeffrey M. Arbeit, Michael E. Burt, Lawrence V. Rubinstein, Catherine M. Gorschboth, and Murray F. Brennan1
Surgical Metabolism Section. Surgery Branch [J. M. A., M. E. B., C. M. G.. M. F. B.J, and Clinical and Diagnostic
National Cancer Institute. NIH. Bethesda. Maryland 20205
ABSTRACT
Glucose and alanine metabolism were investigated in nontumor-bearing (NTB) and tumor-bearing (TB) male F344 rats
after a 24-hr fast and during the infusion of either 0.9% NaCI
solution or glucose at 0.67 or 2.35 mg per 100 g total body
weight per min. During 0.9% NaCI solution infusion, the plasma
glucose level was higher (98.2 ±4.0 versus 85.8 ±8.1 mg
per dl; p < 0.05), the whole-blood láclate level was lower (5.8
± 0.8 versus 8.3 ± 1.6 mg per dl; p < 0.05), the glucose
turnover rate was lower (0.72 ±0.04 versus 0.88 ±0.13 mg
per 100 g total body weight per min; p < 0.05), alanine turnover
rate and the percentage of glucose derived from alanine was
measured by ['"CJalanine in the NTB and compared to the TB
animals.
In response to glucose infusions, the whole-blood lactate
level rose in both groups but remained lower (7.1 ±0.9 versus
10.5 ±2.4 mg per dl at 0.67 mg per 100 g total body weight
per min, p < 0.05; 9.1 ±1.1 versus 19.3 ±5.5 mg per dl at
2.35 mg per 100 g total body weight per min, p < 0.05; NTB
versus TB) in the NTB than in the TB animals. The endogenous
production rate of glucose as measured by [3H]glucose dis
played a similar response to exogenous substrate in the NTB
and TB animals but required a higher plasma glucose concen
tration to effect a similar degree of suppression in the TB
group. The alanine turnover rate rose to a similar level, and the
percentage of glucose derived from alanine was similarly de
pressed in the NTB and TB animals at each glucose infusion
rate.
INTRODUCTION
Nutritional support tailored to the needs of the cancer patient
is dependent upon the elucidation of the metabolism of TB2
hosts in the basal state and in response to exogenous substrate
administration. Since the work of Cori and Cori (8) and Warburg
era/. (48) in the 1920's suggesting the importance of anaerobic
glucose metabolism in the substrate economy of tumors in
various animal models, a number of studies in cancer patients
have centered around carbohydrate metabolism. In the late
1950's, Marks and Bishop (4, 32) demonstrated abnormal
glucose tolerance in cancer patients. In the 1960's, Reichard,
using [14C]glucose, showed that a small proportion of humans
with cancer had abnormally high glucose turnover rates (39).
In the 1970's, both Holroyde e? al. (19) and Waterhouse ef al.
' To whom requests
for reprints
should be addressed,
at Memorial
Sloan
Kettering Cancer Center, 1275 York Avenue, New York, N. Y. 10021.
2 The abbreviations used are: TB, tumor-bearing; NTB, non-tumor-bearing;
TBW. total body weight; R0. turnover rate.
Received March 4, 1981; accepted August 16, 1982.
4936
Trials Section, Biometry Branch [L. V. R.].
(51) commented, respectively, on altered glucose metabolism
and increased gluconeogenesis from alanine in cancer pa
tients. However, studies in humans showing significant altera
tions in carbohydrate metabolism induced by the TB state are
plagued by heterogeneous patient populations, significant an
tecedent weight loss, and lack of appropriate controls (4, 19,
20, 28, 32,38, 39,49, 51).
An animal model was chosen in this experiment which has
been extensively characterized in various studies from this
laboratory (2, 5, 6, 14, 29, 36, 40). The unrestrained rat with
long-term arterial and venous cannulae (5) permits precise
quantification of food intake, nitrogen excretion, and tumor
burden in a homogeneous group with appropriate controls. The
purpose of this study was not only to see whether differences
existed in glucose metabolism and gluconeogenesis from ala
nine during the basal state but also to see if aberrancies in
glucose metabolism, if present, persisted in the face of constant
exogenous substrate administration. Since gluconeogenesis is
known to be suppressed in human controls by glucose admin
istration (25), the percentage of glucose derived from alanine
was also examined to see if it was equivalently suppressed by
exogenous substrate in NTB and TB animals. Alanine was
chosen because of its participation in the glucose-alanine cycle
(11), because of its role as the predominant amino acid re
leased from muscle during acute starvation (37), and because
it is one of the most important glycogenic amino acids taken
up by the liver in the postabsorptive state (41).
MATERIALS
AND METHODS
Animals. Male F344 rats were obtained from Charles River Breed
ing Laboratories (Wilmington, Mass.) and maintained on NIH-5018 rat
chow (Ralston-Purina, St. Louis, Mo.) and tap water ad libitum.
Preparation of Animals. Rats weighing 230 to 250 g were anesthe
tized with sodium pentobarbital, 50 mg/kg ¡.p.;using aseptic tech
nique, the left carotid and right external jugular veins were each
cannulated, and the animals were placed in individual plastic metabolic
cages (Maryland Plastics, New York, N. Y.) (5). Five to 7 days postcatheter implantation, those animals that were to be TB were inoculated
s.c. in the right flank with a suspension of 1 x 106 viable (by trypan
blue exclusion)
cells of a methylcholanthrene-induced
sarcoma (31 ).
When both NTB and TB animals had returned to their preoperative
weight and the TB animals had tumors 2 to 3 cm in diameter, 2-day
food intake was quantified. Both groups were then fasted for 24 hr
with water given ad libitum while urine was collected for total nitrogen
determination by the micro-Kjeldahl method (30). An arterial blood
sample was obtained, and then an i.v. continuous infusion (Harvard
Apparatus, Dover, Mass.) of either 0.9% NaCI solution or glucose at
0.67 or 2.35 mg per 100 g TBW per min was begun (0.67 and 2.35
mg per 100 g TBW per min represent 0.93 and 3.2 times, respectively,
the glucose turnover rate of NTB animals). Six hr later, 10 /iCi D-[33H]glucose(18.1 Ci/mmol)and 5juCiL-{U-"lC]alanine(172
mCi/mmol;
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VOL. 42
Glucose Metabolism and Gluconeogenesis
[l4C]alanine
New England Nuclear, Boston, Mass.) were injected, and arterial blood
samples were obtained at 1, 2, 5, 10, 20, 30, 45, 60, and 90 min after
tracer administration. The animals were sacrificed by air embolization,
and the TBWs, carcass weights, and tumor weights were determined.
Analysis of Intraarterial
Substrate
Levels. Samples of arterial
blood, 220 to 420 n\, were placed in chilled tubes containing 22 to 24
fil sodium heparin (1000 units/ml). Whole-blood aliquots (200 /il) of
the base line and 5- and 60-min blood samples were deproteinized,
and the supernatant was analyzed enzymatically (17). Blood samples
were centrifuged, and the plasma was separated. An aliquot of plasma
was diluted with water, and glucose was measured by a glucose
oxidase method (47) on an autoanalyzer (Technicon Instruments Corp.,
Tarrytown, N. Y.). The remaining plasma underwent membrane filter
centrifugation (Amicon Centriflo Cones, CF50A), and alanine concen
tration was determined on an aliquot of filtrate by a single column
technique (24) on a Beckman 121 MB amino acid analyzer (Beckman
Instruments, Palo Alto, Calif.).
Separation of Radioactive Metabolites. The pH of the filtrate was
adjusted to 2.0 to 2.1 and placed on a cation-exchange
column
(Kontes, Vineland, N. J.) with a 0.5-ml bed volume (18) (AG 50-X8,
200 to 400 mesh; Bio-Rad Laboratories, Richmond, Calif.). The column
was washed with 2.5 ml of water, and the glucose-containing
eluant.
Fraction I, was collected. Amino acids, Fraction II, were removed from
the column by adding 1.5 ml of 2 N NH4OH followed by 1 ml of water.
Fraction I was bought to pH 7 to 8 and placed on an anion-exchange
column with a 1.0-ml bed volume (AGI-X8, 200 to 400 mesh, formate
form; Bio-Rad), followed by 1 ml of water, and the eluant, Fraction la,
during Glucose Infusion
specific activity (dpm/mmol).
Calculations.
The glucose R . and alanine R were calculated using
noncompartmental steady state analysis (22, 23). The glucose mass,
half-life, and space were calculated from the linear regression of the In
specific activity-time curve of [3H]glucose (42). The glucose clearance
(7), the endogenous production rate (total [3H]glucose fl0 - glucose
infusion rate), and the percentage
of glucose derived from alanine
100 / ([l/-'"C]glucose
2 / ([U-'"C]alanine
specific activity)df
specific activity)df
where specific activity is in dpm/mmol] (9, 10, 45, 47), were also
calculated.
Statistical Analysis. Data are expressed as mean ±S.D. Statistical
significance was determined by Student's 2-tailed t test for unpaired
data and by covariance analysis. Since the group sample sizes are
small and there is no assurance that the specific activity values are
normally distributed, the significance levels were confirmed by the
Fisher randomization test for unpaired data (46). The significance
levels obtained by means of the 2 tests were essentially identical.
RESULTS
Food Intake, Nitrogen Balance, and Body Weight. The
food intake did not differ between the NTB and TB animals
(Table 1). The urinary nitrogen balance was significantly less
negative in the TB than in the NTB animals (Table 1). The TBW
was significantly increased but the carcass weight was signifi
cantly decreased in the TB versus the NTB animals (Table 1).
Substrate Levels. During 0.9% NaCI solution infusion, the
whole-blood lactate level was significantly increased in the TB
animals (Table 2). At each glucose infusion rate, the wholeblood lactate incrementally rose in both groups of animals with
a statistically greater level in the TB animals (Table 2). The
plasma glucose concentration remained stable in each group
of animals during infusion (Chart 1). When 0.9% NaCI solution
was collected. Both Fraction la and Fraction II were evaporated to
dryness at room temperature (Savant Instruments, Inc., Hicksville,
N. Y.). The Fraction la residue was reconstituted with water, and
aliquots were taken for glucose concentration measurement and scin
tillation counting (Beckman LS 355) to determine the specific activity
(dpm/mmol) of [3H]glucose and [14C]glucose. The Fraction II residues
was reconstituted with 0.15 N lithium citrate buffer, pH 2.0 (Beckman)
(24) and placed on an amino acid analyzer modified as a fraction
collector (Beckman 121M). Aliquots of the alanine fraction were placed
on a Beckman 121MB amino acid analyzer and counted to determine
Table 1
Body weights, food intake, and nitrogen balance
of TBW8 occu
GroupNTB
(15)"
(g)216.4
(g)216.4
(g)0
wt
wt
intake(g)30.2
food
(mg)-212.8
N balance
tumor0
pied by
±9.0e
±11.9 (15)
± 9.0(15)
(15)
(15)
±3.1 (15)
208.3 ±10.3 (14)Tumor3 17.3 ±8.3(14)%
TB(14)TBW" 225.7 ±7.0 (14)Carcass8
7.7 ±3.7(14)48-hr628.1 ±4.5(14)24-hrc -194.1 ±21.9 (14)
Determined at the end of the experiment after the 24-hr fast and the 6-hr infusion.
'' Measured after animals had regained their postoperative weight loss and just prior to the 24-hr fast.
c Measured during the 24-hr fast prior to the start of the 6-hr infusion.
0 Numbers in parentheses, number of animate.
" Mean ±S.D.
'p<0.05.
Table 2
Whole-blood lactate and plasma glucose concentrations during infusions
The results are expressed as the mean of mean values of multiple time points for each rat.
Lactate (mg/dl)
Infusion
NTB
(6)"7.1
±0.88
solutionGlucose
0.9% NaCI
(5)9.1
±0.9"
mg/100gTBW/min)Glucose
(0.67
mg/100gTBW/min)5.8
(2.35
±1.1df*(4)8.3
Glucose (mg/dl)
TB
(5)10.5±2.4C
±1.6C
(4)19.3
±5.5c'"-e (5)98.2
NTB
(6)134.3
±4.0
(5)160.2
±4.1a
TB
8.1C124.7
±
5.9s170.8
±
±5.4*' (4)85.8
(5)
±12.3*(5)"(4)9
8 Mean ±S.D.
Numbers in parentheses, number of animals.
c p < 0.05 comparison of TB with NTB during each infusion.
p < 0.05 comparison of values during each glucose infusion with values during 0.9% NaCI solution infusion within
each group.
* p < 0.05 comparison of values during 2.35-mg per 100 g TBW per min glucose infusion with values during 0.67mg per 100 g TBW per min glucose infusion within each group.
DECEMBER
1982
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J. M. Arbeit et al.
Plasma Glucose
Concentration
(mg/dl)
200
Glucose
2.35mg/
100g TBW/
min
10.00
100
7.60
-360
0
20
40
TIME (min)
60
80
100
-
5.00
Chart 1. Plasma glucose concentration in response to 6-hr infusions of either
0.9% NaCI solution or glucose at 0.67 or 2.35 mg per 100 g TBW per min. The
data are the mean for each group at each time point. Bars, S.D. The curves
should be broken between —¿360
and O min.
was infused, the plasma glucose concentration was signifi
cantly lower in the TB than in the NTB animals (Table 2).
Infusion of glucose at 0.67 mg per 100 g TBW per min failed
to significantly raise the plasma glucose concentration to an
equivalent level in the TB animals (Table 2). At the glucose
infusion rate of 2.35 mg per 100 g TBW per min, there was no
difference in the elevated plasma glucose levels in both groups
of animals (Table 2). There were no statistical differences
between the plasma alanine levels during 0.9% NaCI infusion
in the TB and NTB animals (2). In response to glucose infusions,
there was a progressive elevation in the plasma alanine levels
in both TB and NTB animals with no statistical difference
between the groups (2).
[3H]Glucose Kinetics. The specific activity-time curves of
the disappearance of [3H]glucose during 0.9% NaCI solution
and incremental glucose infusion are displayed in Chart 2.
Noncompartmental analysis of these curves (22, 23) shows
that during 0.9% NaCI solution infusion there was a statistically
significant increase in the glucose turnover in the clearance
rate in the TB compared to the NTB animals (Table 3). Linear
regression analysis of the In specific activity [3H]glucose-time
curves demonstrates a significantly more rapid glucose half-life
and a similar mass in the TB compared to the NTB animals
(Table 3). In response to glucose infused at 0.67 mg per 100
g TBW per min, there was a decrease in the half-life and
increases in the masses, turnover rates, and clearance rates in
both groups of animals, with statistically significant differences
in the half-life and clearance rates and a borderline significant
difference (p = 0.06) in the turnover rate in the TB compared
to the NTB animals. When glucose was infused at 2.35 mg per
100 g TBW per min, there was an additional decrease in the
half-life and an increase in the mass, turnover rate, and clear
ance rate in both groups, but there were no statistical differ
ences between the TB and NTB animals (Table 3).
Endogenous Glucose Production. The endogenous glucose
production rate, as measured by [3H]glucose kinetics, was
suppressed significantly in the NTB animals infused with glu
cose at 0.67 mg per 100 g TBW per min (Table 3). At this
infusion rate, the TB animals failed to suppress their endoge-
4938
2.50
10
20
30
40
50
60
70
90
Chart 2. Specific activity (S. A Mime curves for [3H]glucose during each in
fusion, normalized for dose (dpm [3H)glucose injected) and TBW of each animal.
The data are presented as the mean values at each time point. The turnover rates
generated by noncompartmental analysis show a statistically significant increase
with increasing glucose infusion within each group and a significant difference
for the NTB (A) versus TB (O) animals infused with 0.9% NaCI solution. The top,
middle, and bottom sets of curves are from animals infused with 0.9% NaCI
solution and glucose at 0.67 and 2.35 mg per 100 g TBW per min, respectively.
nous production and had a statistically significant elevated rate
compared to the NTB animals (Table 3). During glucose infu
sion at 2.35 mg per 100 g TBW per min, the endogenous
glucose production fell to a similar level in both NTB and TB
animals (Table 3).
Linear regression and covariance analysis of the plasma
glucose concentration versus the endogenous production rate
for each individual animal (Chart 3) (NTB, y = -0.00555*
+
1.302; TB, y = -0.00360x
+ 1.263) shows that, despite a
high degree of correlation in the NTB animals, r = —¿0.803
(p
< 0.05), and a low correlation in the TB animals, r = —¿0.364
(p > 0.05), the slopes of these regression lines were similar
(p = 0.56). However, the adjusted cell means were significantly
greater in the TB compared to the NTB animals (p < 0.05).
[14C]Alanine Turnover Rate. The specific activity-time
curves for [14C]alanine are depicted in Chart 4, according to
group and infúsate. Noncompartmental
analysis reveals an
increase in the alanine turnover rate during incremental glucose
infusion with similar results in the NTB and TB animals infused
either with 0.9% NaCI solution or glucose.
Percentage of Glucose Derived from Alanine. The specific
activity-time curves for the appearance of ['"CJalanine are
shown in Chart 5. The percentage
of glucose derived from
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80
TIME (min)
VOL. 42
Glucose Metabolism and Gluconeogenesis
during Glucose Infusion
Table 3
Glucose kinetics during infusions
The [3H]glucose turnover rate is calculated as:
dpm 3H injected
100 x
TBW J ([3H]glucose specific activity) dt
The glucose half-life, mass, and space are calculated
from the linear regression
of the In specific activity-time
curve of [3H]glucose.
The
glucose clearance rate is calculated as
100 x
The endogenous glucose production
glucose turnover rate
plasma glucose concentration
rate is defined as total | 'H]glucose turnover rate - glucose infusion rate.
rate
(mg/100 g
TBW/min)0.72
(mg/ 100
(min)24.4
TBW)25.5
g
±2.4b
(6)"
NaCI solution
± 2.4
17.8 ±2.1°
0.88
TB(5)
22.5 ± 3.4
19.2
±1.6d
35.5
± 3.0d
NTB (5)
0.67mg/100gTBW/min
1.29
16.7 ±1.2C
1.68
TB(4)
40.2 ± 8.8
12.9
±1.9d'e
50.0
±
5.3d'8
2.69
2.35 mg/100 g TBW/minGroupNTBNTB (4)
54.5 ±10.2oTurnover
2.76
TB(5)Half-life 13.6 ±0.8™Mass
Infusion0.9%
rate
(ml/ 100 g TBW/
min)0.73
glu
cose production
rate (mg/ 100 g
TBW/min)0.72
±0.04
±0.13C
±0.02
±0.04
1.03 ±0.12°
0.88 ±0.13
0.64
±0.07d
0.96
±0.1"(6)
±0.10
±0.38d
1.34 ±0.27°'d 1.05 ±0.38C
±0.20tÃ--e 1.70 ±0.14"'"
0.35 ±0.170-8
±0.43d'eClearance
1.62 ±0.24dEndogenous
0.53 ±0.42
Numbers in parentheses, number of animals.
" Mean ±S.D.
cp< 0.05 comparison of TB with NTB during each infusion.
" p < 0.05 comparison of values during each glucose in fusion with values during 0.9% NaCI solution infusion within each group.
8 p < 0.05 comparison of values during 2.35-mg per 100 g TBW per min glucose infusion with values during 0.67-mg per 100 g TBW per
min glucose infusion within each group.
2.0
o _
O e
£E
U) ?
>e LO
lo
75
100
125
150
175
200
PLASMA GLUCOSE CONCENTRATION (mg/dl)
Chart 3. Graphic analysis of the response of the endogenous glucose pro
duction rate to prevailing plasma glucose concentrations. The data represent the
plasma glucose concentration of each animal and the resultant endogenous
glucose production rate: NTB (A), y = -0.00555x
+ 1.302; TB (O), y -0.0036X
+ 1.263. Covariance analysis showed equality of slopes but a
statistically significant higher group mean in the TB compared to the NTB animals.
alanine decreases progressively in response to incremental
glucose infusion to a similar degree in both NTB and TB animals
(Table 4).
DISCUSSION
In this study, abnormalities of basal glucose metabolism were
demonstrated in TB compared to NTB animals when the tumor
comprised 7.7 ± 3.7% of the TBW, before the onset of de
creased food intake, increased nitrogen excretion, and pro
gressive TBW loss. These differences in glucose metabolism
persisted during exogenous glucose administration. Basal al
anine metabolism and the percentage of glucose derived from
DECEMBER
1982
alanine were not significantly different in the TB animals com
pared to the NTB animals, and this lack of significant difference
between the groups also persisted during glucose infusion.
Previous work in our laboratory demonstrating abnormal
glucose metabolism and gluconeogenesis from alanine in TB
compared to NTB rats was based on animals in their fourthday post-superior vena cava cannulation, with tumor burdens
of 15 to 20% of the TBW and significantly lower carcass
weights (29). With the use of a single superior vena cava
catheter for simultaneous tracer injection and substrate infu
sion, it is difficult to obtain blood samples at rapid intervals and
to ensure that they are not contaminated. However, to accu
rately define glucose and alanine kinetics, it is important to
obtain early, multiple time points; thus, in our previous studies,
alanine kinetics was calculated indirectly by assumptions as to
glucose derived from alanine entering the glucose decay curve
(29). In addition, rats at the fourth day postcannulation may
still be recovering from the operative procedure (5), and pre
vious reports in the literature have shown how carbohydrate
metabolism can be altered by trauma (1, 26, 52).
The transplantable, methylcholanthrene-induced
sarcoma
used in this study is first palpable at Day 14 after s.c. flank
injection of 1 x 106 viable cells and kills the animal when it
occupies 30 to 35% of the TBW, 35 to 40 days postinoculation
(36). Thus, the animals used in this experiment were studied in
the first quarter of their disease process, and their tumor
burdens were comparable to those of humans with large retroperitoneal sarcomas or extensive leukemic-lymphomatous
bone and extramedullary involvement (12, 27).
The equivalent food intake of the TB and NTB animals in this
study eliminated prior starvation as a cause for the altered
glucose metabolism in the tumor bearers (35). The significantly
less negative nitrogen balance in the TB compared to the NTB
animals was previously documented by Mider in rats with and
without Walker 256 carcinomas (34). This "nitrogen trap" (34)
phenomenon has been reported by Waterhouse ef a/. (50) in
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J. M. Arbeit et al.
90
Chart 4. Specific activity (S.A. Mime curves for [14C]alanine during each in
fusion normalized similar to curves in Chart 2. The data are the mean values at
each time point. The turnover rates generated by noncompartmental analysis
show a statistically significant increase within each group (Table 4) with no
patients with leukemias and lymphomas. In the presence of this
relative nitrogen avidity and in spite of their significantly greater
TBW's, the TB animals still had depressed carcass weights
compared to the NTB animals. Mider demonstrated this same
result; the carcasses of his TB rats contained less lipid (33)
and nitrogen (34) than did the NTB controls, and the "lost"
nitrogen was found sequestered in the tumor (34).
The stable plasma glucose levels during infusion of either
0.9% NaCI solution or exogenous glucose demonstrated that
both groups of animals were in the steady state. The statistically
significantly decreased basal plasma glucose and increased
whole-blood lactate levels in the TB animals have been shown
in previous work from this laboratory (6) and others (43).
Studies involving in vivo tumor preparations growing in ap
pendages (8, 48) or on isolated vascular pedicles (16) have
documented high rates of glucose consumption and lactate
production by tumors.
In response to glucose infused at 0.67 mg per 100 g TBW
per min, there was a statistically significantly higher wholeblood lactate level in the TB animals despite a significantly
lower plasma glucose concentration. With a similar degree of
hyperglycemia during glucose infusion at 2.35 mg per 100 g
TBW per min, the lactate level was twice as high in the TB as
in the NTB animals. One possible explanation for this greater
rise in lactate concentration during glucose infusion in the TB
compared to the NTB animals was demonstrated in isolated in
vivo tumor preparations in which the capacity of the tumor for
glucose uptake was unaffected by hyperglycemia and the
effluent lactate concentration was increased (16). Clinically,
4940
difference between the NTB (A) and TB (O) animals. Top, middle, and bottom
sets of curves are from animals infused with 0.9% NaCI solution and glucose at
0.67 and 2.35 mg per 100 g TBW per min, respectively.
there have been reports of cancer patients receiving high
glucose infusion rates in the form of total parenteral nutrition
who were either in moderate lacticacidemia (20) or frank lactic
acidosis (15).
The lack of significant difference in the plasma alanine con
centration during 0.9% NaCI solution or glucose infusion (2)
implies that glucose shunting via the alanine cycle (11 ) is not
increased in the TB compared to the NTB animals and stands
in contrast to the above-noted differential lactate response.
The close agreement of the glucose kinetic data in the NTB
animals from this experiment with that reported from this lab
oratory (6) and others (3, 9, 21, 22, 44) strengthens the
differences demonstrated between the NTB and TB animals in
this study.
The significantly elevated glucose turnover and clearance
rates of the TB animals infused with 0.9% NaCI solution are
nearly identical to the data reported by Burt using the same
noncachectic animal-tumor system but with i.p. tracer admin
istration (6). This increased glucose turnover rate shown in TB
animals is distinct from starvation which results in a decrease
in the turnover rate (13).
During glucose infusion at 0.67 mg per 100 g TBW per min,
the significantly increased glucose clearance rate in the TB as
compared to the NTB animals demonstrates that the aberrant
glucose kinetics of the TB state persists during moderate rates
of exogenous substrate administration. When glucose was
infused at 2.35 mg per 100 g TBW per min, the kinetic
differences between the TB and NTB groups disappeared,
suggesting either that the TB animal was saturated with subCANCER
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VOL. 42
Glucose Metabolism and Gluconeogenesis
during Glucose Infusion
strate or, given the increased láclate level, that there was
increased conversion of the infused glucose into this substrate
in the TB animal.
In response to incremental glucose infusion and the resultant
increase in the plasma glucose, the endogenous glucose pro
duction rate clearly was suppressed in the NTB animals. The
TB animals behaved in a more complex manner, having a
persistently elevated endogenous production rate compared to
the NTB group when glucose was infused at 0.67 mg per 100
g TBW per min which then fell to a similar level when glucose
was infused at 2.35 mg per 100 g TBW per 100. The data from
the covariance analysis of Chart 3 reveal that the response of
the endogenous glucose production rate to the prevailing
plasma glucose concentration was basically similar in the NTB
and TB animals but that the TB animals required a higher
plasma glucose concentration to effect a similar reduction in
this rate.
In contrast to the glucose kinetic data, there were no signifi
cant differences in the alanine turnover rates during 0.9% NaCI
solution or glucose infusion between the TB and NTB animals.
Coupled with the lack of significant differences in the percent
age of glucose derived from alanine, these data suggest that
abnormalities in glucose kinetics found in TB animals during
0.9% NaCI solution or exogenous glucose administration are
not due to an increased percentage of glucose derived from
alanine. However, if data from conversion of [14C]alanine to
[14C]glucose are expressed as a percentage of 3-3H-derived
Chart 5. Appearance of the specific activity (S.A 1 of |"C|glucoso, derived
from the injected [U-"C]alanine, over time during each infusion. Normalized
similar to data in Chart 2. Data are the mean values at each time point. The
curves are arranged with respect to infusion similar to curves in Charts 2 and 4.
A. NTB; O, TB.
Table 4
Percentage of glucose derived from alanine and the alanine turnover rate
The percentage of glucose from alanine is calculated as:
100 J (["CJglucose specific activity)«
2 / <['4C]alanine specific activity) dt
The alanine turnover rate is:
dose (dpm ['"CJalanine injected)
' TBW / (( ' 4Cplanine specific activity)
dtInfusion0.9%
solution0.67mg/100g
NaCI
(5f-b
TB(5)NTB
TBW/
(4)b
TB(4)NTB
min2.35
of glucose
alanine4.00
from
±1.06°
turnover
rate (nmol/ 100 g
min)0.93
TBW
4.14
0.942.37
±
±0.24
0.88
0.251.41
±
±0.29d
0.43d0.84
2.55 ±
±0.09d
0.33d2.20
1.57 ±
±0.28dl"
±0.21d'8
(4)
mg/100 g TBW/
0.96 ±0.20d'eAlanine
2.51 ±0.54d-e
TB(5)%
minGroupNTB
"' Numbers in parentheses, number of animals.
In a animals, alanine kinetics was not obtainable.
c Mean ±S.D.
d p < 0.05 comparison of values during each glucose infusion with values
during 0.9% NaCI solution infusion within each group.
" p < 0.05 comparison of values during 2.35-mg per 100 g per TBW per min
glucose infusion with values during 0.67-mg per 100 g TBW per min glucose
infusion within each group.
DECEMBER
1982
glucose turnover, an apparent increase in the amount of glu
cose derived from alanine (3.2 to 4.8%) occurs in TB animals
at high glucose loads. This calculation we believe to be unjus
tified, inasmuch as the sensitivity to error is high and the
[14C]glucose specific activity is subject to recycling. Any com
ment on increased cycling of glucose to alanine must await
more definitive experiments.
In conclusion, the results of this experiment define a unique
state of glucose metabolism in the TB animals not explicable in
terms of antecedent starvation or increased stress or injury.
The increased glucose turnover of the TB animal during
0.9% NaCI solution infusion is a different response to the
progressive decrease seen in starvation. The significantly
greater rise in whole blood lactate during glucose infusion in
this group implies continual glucose uptake and conversion to
lactate by the tumor in the face of hyperglycemia.
The increased clearance and endogenous glucose produc
tion rates during glucose infusion at 0.67 mg per 100 g TBW
per min demonstrate that glucose kinetic abnormalities persist
during moderate rates of exogenous substrate administration.
The lack of difference in the percentage of glucose derived
from alanine and the alanine turnover rates during 0.9% NaCI
solution infusion, coupled with the relative nitrogen avidity
during the 24-hour fast, is strong support that gluconeogenesis
from alanine is not increased in TB animals when antecedent
food intake is equivalent to that of NTB animals. The compa
rable suppression of the percentage of glucose derived from
alanine by glucose infusion shows that TB animals are not like
septic postoperative patients (25) and that glucose derived
from alanine probably plays a minor role in the substrate
economy of the TB host.
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CANCER
RESEARCH
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VOL.
42
Glucose Metabolism and the Percentage of Glucose Derived
from Alanine: Response to Exogenous Glucose Infusion in
Tumor-bearing and Non-Tumor-bearing Rats
Jeffrey M. Arbeit, Michael E. Burt, Lawrence V. Rubinstein, et al.
Cancer Res 1982;42:4936-4942.
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