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Glucagon and fetal growth in the rat
Glucagon and fetal growth in the rat JOHN
E.
TYSON*
ROBERT J.
A.
A. F.
London,
H.
KINCH
STEVENSON
Ontario,
Canada
Increased size is characteristic of the offspring of diabetic mothers and there is evidence that hyperglycemia itself may have a similar effect in the rat. Glucagon, the second known pancreatic hormone, causes a hyperglycemia through its enhancement of hepatic glycogenolysis. The eflect of the regular administration of glucagon to the mother during the last part of pregnancy in the rat has, therefore, been investigated with 300 pg of crystalline glucagon injected subcutaneously at 9:00 A.M. and 3:00 P.M. from day 17 to day 21 of pregnancy. Maternal weight gain was decreased, along with daily food intake, when compared to saline-injected pregnant rats. The glucagon failed to produce a persistent hyperglycemia. A significant decrease in mean weight of the pups in the glucagon-treated group could not be attributed to the reduction of maternal food intake alone, for these pups were also significantly lighter than those from rats pair-fed with the glucagon-treated animals. This failure of weight gain may have been due to an increase in metabolic rate and caloric demand that glucagon can produce. Glucagon had only a temporary e#ect on blood glucose; it acutely reduced the maternal liver glycogen but had little effect on placental glycogen.
Chow diet in stock cages prior to experimentation. During the experimental period all were placed on semisynthetic diets providing 58 per cent fat, 20 per cent protein, and 22 per cent carbohydrate. Water was allowed ad libitum. The rats were divided into three groups. In Group I, 16 virgin rats were used. Eight received subcutaneous injections of 0.3 ml. of a sterile glycerine solution containing 300 pg of crystalline glucagon” at 9:OO .4.&r. and 3:00 P.M. daily for 5 consecutive days. Eight control animals received saline injections at similar time intervals. Group II consisted of 8 female rats who were placed with males of proved fertility. The appearance of sperm in the vaginal smear was considered day 0 of pregnancy and the females were then placed in individual cages. Four received subcutaneous injections of 300 pg of crystalline glucagon dissolved in 0.3 ml. of an 0.2M glycine buffer twice daily for the last 5 days of pregnancy. The
I T I s K N 0 w N that fetal and plaCeId weight are increased in alloxan-diabetic maternal rats1 and in rats in which hyperglycemia has been induced with constant glucose infusion.* Repeated injections of glucagon, the second pancreatic hormone, will produce hyperglycemia through the release of hepatic glycogen. 3 Such hyperglycemia might result in fetuses of excessive size, similar to those obtained from alloxan-diabetic gestational animals. To test this hypothesis, the following experiments were carried out. Materials
and
methods
Virgin Sprague-Dawley rats weighing 200 to 250 grams were used. All received Master’s From The Departments of Physiology and Obstetrics and Gynecology, University of Western Ontario. Supported by a grant from The Department of National Health and Welfare, Child and Maternal Health Grant 605-13-30. *Present address: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland.
M.
834
*Lot No. A. Root,
258-234B-167-1. Generously supplied by Dr. Eli Lilly & Company, Indianapolis, Indiana.
Glucagon
in nonpregnant Total
Group
tP =
< 0.001.
growth
(grams)
835
Glucagon-treated nonpregnant animals (Table I). The experimental animals became anorexic within 24 hours of receiving the first glucagon injection. Food intake gradually decreased until the average daily consumption on the fifth day was less than 2 Gm. Profound weight loss accompanied the decrease in food intake (Fig. 1). The blood glucose levels were persistently elevated in the glucagon-treated animals. Glycosuria was detected in half. At laparotomy the hepatic tissue appeared gray in those animals receiving glucagon. Liver glycogen was sixnificantly depleted in these animals.
Glucagon-treated
pregnant rats (Table
II).
Pregnancy appeared to reduce the effects of giucagon. Average daily food intake was reduced to 5.4 Gm., similar to the intake of the nonpregnant glucagon-treated animals. Maternal weight gain was significantly reduced. Water intake was increased despite decreased food intake. This polydypsia was not accompanied by a persistent hyperglycemia as normal fasting values for blood glucose were obtained in all animals. None of the rats aborted.
Effect of glucagon on fetal rat (Table III). Litter weight was not significantly de-
female
rats !
O-7*
In rat
Results
weight
change, days Control (saline, 8 animals) Experimental (glwagon, 8 animals j *Mean 2 S.E.M.
fetal
moved and frozen in dry ice. Glycogen determinations were carried out by the method of Russell and Bloom.7 In the pregnant animals, the uterine vessels were clamped and the uterine horns removed in toto. Eac1-i fetus was dissected free of its placenta :tnd amniotic sac and weighed. Fetal 1~100~1 was obtained by decapitation. Every third placenta was frozen for subsequent ,glvcogtn determination.
control group followed an identical injection schedule with saline. Group III included 9 pregnant rats, 3 of which received subcutaneous injections of glucagon as described for Group II (vide supra) . The remaining 6 animals served as saline controls, of which 3 were pair-fed controls for the glucagon-treated animals. From the fourteenth day of gestation the food intake of the glucagon-treated animals was measured and for the last 7 days of Sestation the pair-fed controls received a limited food ration equal only to their pairmates’ ingestion the previous day. Tail blood was obtained from each rat twice daily 15 minutes prior to each injection. Blood glucose determinations were carried out by the micro-method of Nelson4 and Somogyi.5 Mean values were calculated from all values obtained between day 17 and day 21 of treatment in the gestational rat or day 1 to 7 in the nonpregnant animal. Maternal weight gain and food and water intake were measured each morning at 8: 00 A.M. throughout pregnancy or for 7 days in the nonpregnant group. On the fifth day of injections, or day 21 in the case of the pregnant rats, a laparotomy or cesarean section was performed as follows: At 1430 hours tail blood was obtained for blood glucose determination. Each rat then received an intraperitoneal injection of 0.3 ml. of pentobarbital sodium (Abbott, 0.3 mg. per kilo,gram ), , an anesthetic agent having the least effect on reducing liver glycogen and blood glucose levels6 The afternoon dose of gluc’agon was injected 15 minutes after the anesthetic agent. When the rat was anesthetized, the abdomen was opened. The right lobe of the maternal liver was quickly re-
Table I. Effects of glucagon
and
Food
intake* (cm.)
Blood glucose* (mg./lOO ml.)
Laparotoq liuer glycogen* f%)
7.3 2 1.21
11.6 + 0.78
93.2 + 2.13
4.2 + 0.26
-10.8 ” 2.41t
6.4 + 0.96t
128.8 r 6.52t
1.6 t O:ilt
836
Tyson,
Kinch,
and
July 15, 1Wl Am. J. Obst. & Gynrr.
Stevenson
55
_
iii s 5
-4
m
-8
3
2
‘\,I \
-
6
DAYS \
\
\ \
\
\
\
-12
‘\
-I
\
3
-16
t
5
4
-
CONTROL
----
GLUCAGON
(8) (8)
\
-24
Fig. 1. Weight
Fig. 2. The treated.
change
effect
in grams
of female
rats.
of glucagon
on fetal
size.
creased. Mean pup weight, however, was low in the glucagon series, with the smallest pups weighing less than 4 grams. Fetal blood glucose concentrations were not elevated. Significant differences were found in maternal liver glycogen concentrations and in
Upper
pup
=
control;
fetal placental treated group.
lower
pup
glycogen
=
glucagon
content
in
the
Glucagon treatment of pregnant ratspair-fed fetal studies (Table IV). At cesarean section all fetuses evidence of resorption
were was
alive and no noted. When
Volume Number
Glucagon
101 6
Table II. Effect of glucagon
on the pregnant
and fetal growth
rat
Maternal weight Food intdke gain as *% conception weight, days during treatment* o-21* (Gm.)
Control (saline, 4 litters) Experimental (glucagon, litters) -_ *Mean +- S.E.M. tDifference from
controls
+ 7.36
28.4 ___-_
t 3.61t.
9.5 rf: 1.06
26.5
C 2.10
96 2 2.6
__.
5.4 +_ 0.52t
38.7
2 3.79t
98228
P < 0.05.
on the fetal rat Glycogen
Mean weight”
Control (saline, 4 litters) Experimental (glu____cagon, 4 litters) “Mean DTotal
Maternal blood glucose concentration/lOO ml.+
Water intake” (Gm./day)
!
Group
.--. ~-
4
Table III. Effect of glucagon -.-__I_
49.3
Mean
litter (grams)
Pup blood glucose concentration” /IO0 ml.
pup weight* (crams)
51.2
f
2.12
5.41
40.7
f 4.36
4.43
% 0.12
Maternal liver
concentration* i’jl,) / /
Placental
99 +_ 11.2
2.43 +_ 0.404
0.23 1 0.009
89 t
0.48 2 0.1463
0.16 f 0.019$
38t t 0.12$ 37t
13.9
+ S.E.M. number of pups.
tDifference
from
controls
P < 0.05.
Table IV. Effect body weight
of glucagon in the rat
on maternal
food intake
and on maternal
--
and fetal
-_____--.-Group
Controls
Saline,
3 animals
Glucagon,
3 animals
Controls
Pair-fed, Saline, *Mean tNo.
837
..__ _I___--.-.._--
-
Group
in rat
3 animals 3 animals
Maternal gain*
weight (grams)
Food intake days 17-20* (Gm.)
60 21.5
weight*
12.3 t1.14
5.53 20.086 (39)1-
10.5
43 ‘6.4
4.96
r2.14
P
YJ.06 136):
10.5 ‘2.14
44 kg.8
f S.E.M.
Pup
.
i
-
5.26 fO.07 (37)f
_
(grams) 1 / I’<(!’
001
J ; 1. 1’<(1.001 / j
of pups.
pregnant control animals were pair-fed the food intake of a glucagon-treated maternal rat, maternal weight gain paralleled the experimental animals. Greatest differences were seen in the effect on pup weight. While the weights of fetuses of pair-fed animals were s&ificantly lower than the saline controls, statistically significant differences were found between the pair-fed and the glucagontreated fetuses as well as between the normal saline controls. Maternal and fetal blood
glucose levels remained similar to those of Group II. Maternal liver glycogen (not shown) was significantly decreased in these glucagon-treated animals as in Table III. Placental glycogen content did not vary. Comment
Glucagon produces anorexia and weight loss in pregnant and nonpregnant rats, while weight loss is not as marked in the gestational animal. Blood ,ylllcose failPc1 to re-
838
Tyson,
Kinch,
and
Stevenson
July
15. I9G8
Am. J. Obst. & Gyner.
main elevated in pregnant animals while glucagon produced persistent hyperglycemia in the nonpregnant rat. A diabetic-like state was produced in the nonpregnant animal with polydypsia, hyperglycemia, and glycosuria. This is modified by pregnancy to include only polydypsia. Blood glucose might escape to the fetus in pregnancy as seen in lower maternal fasting blood glucose levels. The normal fasting values in late pregnancy in animals receiving glncagon may represent a decrease in available glucose stores resulting in increased catabolism. Retardation of fetal growth in the rat occurs under numerous circumstances. Knobil and Caton performed hypophysectomy on 12 day gestational rats and found a decrease in feta1 and pIacenta1 weights at birth. The effect was not due to a decreased food intake. He concluded that the fetal pituitary might control intrauterine growth in the rat. The administration of protamine-zincinsulin to maternal rats significantly reduced fetal and placental weights. Stillbirths and fetal anomalies were also increased.” lo The effect of hypophysectomy and insulin on fetal growth might represent a compromise in placental function with changes in placental perfusion and metabolism adversely affecting intrauterine development.
Glucagon affects fetal growth in the rat. Some have attributed this to an increase in protein catabolism. l1 Glucagon does increase the basal metabolic rate,12 but this is a modest rise. Our results suggest that glucagon affects fetal growth independent of decreased food intake. Since glucagon is beta cytotropic,13 its effect may be mediated through an augmented insulin release and a state of hyperinsulinism. Glucose would therefore be utilized by the maternal tissues, reducing the amount available for placental and fetal use. Glucagon appears to affect placental glycogen stores. No direct evidence is available at present to support this effect. It is felt that the decreased placental concentration may be secondary to maternal hepatic glycogen depletion. Pregnancy is a catabolic state for the maternal organism providing as much glucose as necessary for the growing fetus. This is achieved by the mobilization and metabolism of lipid and protein depots. When food intake alone is decreased, the fetus suffers a reduction in weight. There is a corresponding decrease in placental weight. Regular daily injections of glucagon to maternal rats result in the birth of offspring of decreased weight.
REFERENCES
Love, E. J., Kinch, R. A. H., and Stevenson, I. A. F.: AM. J. OBST. & GYNEC. 80: 536, i960. 2. Harding, P. G. R., Kinch, R. A. H., and Stevenson, J. A. F.: Diabetes 11: 321, 1962. 3. Sokal, J.: Am. J. Med. 41: 331, 1966. N.: 1. Biol. Chem. 153: 375, 1944. 4. Nelson. M.: J. Biol. Chem. 195: 19, 1952. 5. Somog$i, J. E.: Unpublished data, 1962. 6. Tyson, J. A., and Bloom, W.: Endocrinology 7. Russell, 58: 83, 1956. a. Knob& E., and Caton, W. E.: Endocrinology 53: 198, 1953. 1.
9.
10.
11.
12. 13.
Lichtenstein, H., Guest, G. M., and Warkany, J.: Proc. Sot. Exper. Biol. & Med. 78: 398, 1961. Love, E. J., Kinch, R. A. H., and Stevenson, J. A. F.: Proc. Canad. Fed. Biol. SC. IV: 40, 1961. Holloway, S., Stevenson, J, A. F., and Kinch, R. A. H.: Canad. J. Physiol. & Pharmacol. 43: 473, 1965. Salter, J., and Best, C. H.: Nature 180: 1124, 1957. Samols, E., Marri, G., and Marks, V. A.: Diabetes 15: 855, 1966.
E.
TYSON*
ROBERT J.
A.
A. F.
London,
H.
KINCH
STEVENSON
Ontario,
Canada
Increased size is characteristic of the offspring of diabetic mothers and there is evidence that hyperglycemia itself may have a similar effect in the rat. Glucagon, the second known pancreatic hormone, causes a hyperglycemia through its enhancement of hepatic glycogenolysis. The eflect of the regular administration of glucagon to the mother during the last part of pregnancy in the rat has, therefore, been investigated with 300 pg of crystalline glucagon injected subcutaneously at 9:00 A.M. and 3:00 P.M. from day 17 to day 21 of pregnancy. Maternal weight gain was decreased, along with daily food intake, when compared to saline-injected pregnant rats. The glucagon failed to produce a persistent hyperglycemia. A significant decrease in mean weight of the pups in the glucagon-treated group could not be attributed to the reduction of maternal food intake alone, for these pups were also significantly lighter than those from rats pair-fed with the glucagon-treated animals. This failure of weight gain may have been due to an increase in metabolic rate and caloric demand that glucagon can produce. Glucagon had only a temporary e#ect on blood glucose; it acutely reduced the maternal liver glycogen but had little effect on placental glycogen.
Chow diet in stock cages prior to experimentation. During the experimental period all were placed on semisynthetic diets providing 58 per cent fat, 20 per cent protein, and 22 per cent carbohydrate. Water was allowed ad libitum. The rats were divided into three groups. In Group I, 16 virgin rats were used. Eight received subcutaneous injections of 0.3 ml. of a sterile glycerine solution containing 300 pg of crystalline glucagon” at 9:OO .4.&r. and 3:00 P.M. daily for 5 consecutive days. Eight control animals received saline injections at similar time intervals. Group II consisted of 8 female rats who were placed with males of proved fertility. The appearance of sperm in the vaginal smear was considered day 0 of pregnancy and the females were then placed in individual cages. Four received subcutaneous injections of 300 pg of crystalline glucagon dissolved in 0.3 ml. of an 0.2M glycine buffer twice daily for the last 5 days of pregnancy. The
I T I s K N 0 w N that fetal and plaCeId weight are increased in alloxan-diabetic maternal rats1 and in rats in which hyperglycemia has been induced with constant glucose infusion.* Repeated injections of glucagon, the second pancreatic hormone, will produce hyperglycemia through the release of hepatic glycogen. 3 Such hyperglycemia might result in fetuses of excessive size, similar to those obtained from alloxan-diabetic gestational animals. To test this hypothesis, the following experiments were carried out. Materials
and
methods
Virgin Sprague-Dawley rats weighing 200 to 250 grams were used. All received Master’s From The Departments of Physiology and Obstetrics and Gynecology, University of Western Ontario. Supported by a grant from The Department of National Health and Welfare, Child and Maternal Health Grant 605-13-30. *Present address: Department of Gynecology and Obstetrics, Johns Hopkins University School of Medicine, Baltimore, Maryland.
M.
834
*Lot No. A. Root,
258-234B-167-1. Generously supplied by Dr. Eli Lilly & Company, Indianapolis, Indiana.
Glucagon
in nonpregnant Total
Group
tP =
< 0.001.
growth
(grams)
835
Glucagon-treated nonpregnant animals (Table I). The experimental animals became anorexic within 24 hours of receiving the first glucagon injection. Food intake gradually decreased until the average daily consumption on the fifth day was less than 2 Gm. Profound weight loss accompanied the decrease in food intake (Fig. 1). The blood glucose levels were persistently elevated in the glucagon-treated animals. Glycosuria was detected in half. At laparotomy the hepatic tissue appeared gray in those animals receiving glucagon. Liver glycogen was sixnificantly depleted in these animals.
Glucagon-treated
pregnant rats (Table
II).
Pregnancy appeared to reduce the effects of giucagon. Average daily food intake was reduced to 5.4 Gm., similar to the intake of the nonpregnant glucagon-treated animals. Maternal weight gain was significantly reduced. Water intake was increased despite decreased food intake. This polydypsia was not accompanied by a persistent hyperglycemia as normal fasting values for blood glucose were obtained in all animals. None of the rats aborted.
Effect of glucagon on fetal rat (Table III). Litter weight was not significantly de-
female
rats !
O-7*
In rat
Results
weight
change, days Control (saline, 8 animals) Experimental (glwagon, 8 animals j *Mean 2 S.E.M.
fetal
moved and frozen in dry ice. Glycogen determinations were carried out by the method of Russell and Bloom.7 In the pregnant animals, the uterine vessels were clamped and the uterine horns removed in toto. Eac1-i fetus was dissected free of its placenta :tnd amniotic sac and weighed. Fetal 1~100~1 was obtained by decapitation. Every third placenta was frozen for subsequent ,glvcogtn determination.
control group followed an identical injection schedule with saline. Group III included 9 pregnant rats, 3 of which received subcutaneous injections of glucagon as described for Group II (vide supra) . The remaining 6 animals served as saline controls, of which 3 were pair-fed controls for the glucagon-treated animals. From the fourteenth day of gestation the food intake of the glucagon-treated animals was measured and for the last 7 days of Sestation the pair-fed controls received a limited food ration equal only to their pairmates’ ingestion the previous day. Tail blood was obtained from each rat twice daily 15 minutes prior to each injection. Blood glucose determinations were carried out by the micro-method of Nelson4 and Somogyi.5 Mean values were calculated from all values obtained between day 17 and day 21 of treatment in the gestational rat or day 1 to 7 in the nonpregnant animal. Maternal weight gain and food and water intake were measured each morning at 8: 00 A.M. throughout pregnancy or for 7 days in the nonpregnant group. On the fifth day of injections, or day 21 in the case of the pregnant rats, a laparotomy or cesarean section was performed as follows: At 1430 hours tail blood was obtained for blood glucose determination. Each rat then received an intraperitoneal injection of 0.3 ml. of pentobarbital sodium (Abbott, 0.3 mg. per kilo,gram ), , an anesthetic agent having the least effect on reducing liver glycogen and blood glucose levels6 The afternoon dose of gluc’agon was injected 15 minutes after the anesthetic agent. When the rat was anesthetized, the abdomen was opened. The right lobe of the maternal liver was quickly re-
Table I. Effects of glucagon
and
Food
intake* (cm.)
Blood glucose* (mg./lOO ml.)
Laparotoq liuer glycogen* f%)
7.3 2 1.21
11.6 + 0.78
93.2 + 2.13
4.2 + 0.26
-10.8 ” 2.41t
6.4 + 0.96t
128.8 r 6.52t
1.6 t O:ilt
836
Tyson,
Kinch,
and
July 15, 1Wl Am. J. Obst. & Gynrr.
Stevenson
55
_
iii s 5
-4
m
-8
3
2
‘\,I \
-
6
DAYS \
\
\ \
\
\
\
-12
‘\
-I
\
3
-16
t
5
4
-
CONTROL
----
GLUCAGON
(8) (8)
\
-24
Fig. 1. Weight
Fig. 2. The treated.
change
effect
in grams
of female
rats.
of glucagon
on fetal
size.
creased. Mean pup weight, however, was low in the glucagon series, with the smallest pups weighing less than 4 grams. Fetal blood glucose concentrations were not elevated. Significant differences were found in maternal liver glycogen concentrations and in
Upper
pup
=
control;
fetal placental treated group.
lower
pup
glycogen
=
glucagon
content
in
the
Glucagon treatment of pregnant ratspair-fed fetal studies (Table IV). At cesarean section all fetuses evidence of resorption
were was
alive and no noted. When
Volume Number
Glucagon
101 6
Table II. Effect of glucagon
on the pregnant
and fetal growth
rat
Maternal weight Food intdke gain as *% conception weight, days during treatment* o-21* (Gm.)
Control (saline, 4 litters) Experimental (glucagon, litters) -_ *Mean +- S.E.M. tDifference from
controls
+ 7.36
28.4 ___-_
t 3.61t.
9.5 rf: 1.06
26.5
C 2.10
96 2 2.6
__.
5.4 +_ 0.52t
38.7
2 3.79t
98228
P < 0.05.
on the fetal rat Glycogen
Mean weight”
Control (saline, 4 litters) Experimental (glu____cagon, 4 litters) “Mean DTotal
Maternal blood glucose concentration/lOO ml.+
Water intake” (Gm./day)
!
Group
.--. ~-
4
Table III. Effect of glucagon -.-__I_
49.3
Mean
litter (grams)
Pup blood glucose concentration” /IO0 ml.
pup weight* (crams)
51.2
f
2.12
5.41
40.7
f 4.36
4.43
% 0.12
Maternal liver
concentration* i’jl,) / /
Placental
99 +_ 11.2
2.43 +_ 0.404
0.23 1 0.009
89 t
0.48 2 0.1463
0.16 f 0.019$
38t t 0.12$ 37t
13.9
+ S.E.M. number of pups.
tDifference
from
controls
P < 0.05.
Table IV. Effect body weight
of glucagon in the rat
on maternal
food intake
and on maternal
--
and fetal
-_____--.-Group
Controls
Saline,
3 animals
Glucagon,
3 animals
Controls
Pair-fed, Saline, *Mean tNo.
837
..__ _I___--.-.._--
-
Group
in rat
3 animals 3 animals
Maternal gain*
weight (grams)
Food intake days 17-20* (Gm.)
60 21.5
weight*
12.3 t1.14
5.53 20.086 (39)1-
10.5
43 ‘6.4
4.96
r2.14
P
YJ.06 136):
10.5 ‘2.14
44 kg.8
f S.E.M.
Pup
.
i
-
5.26 fO.07 (37)f
_
(grams) 1 / I’<(!’
001
J ; 1. 1’<(1.001 / j
of pups.
pregnant control animals were pair-fed the food intake of a glucagon-treated maternal rat, maternal weight gain paralleled the experimental animals. Greatest differences were seen in the effect on pup weight. While the weights of fetuses of pair-fed animals were s&ificantly lower than the saline controls, statistically significant differences were found between the pair-fed and the glucagontreated fetuses as well as between the normal saline controls. Maternal and fetal blood
glucose levels remained similar to those of Group II. Maternal liver glycogen (not shown) was significantly decreased in these glucagon-treated animals as in Table III. Placental glycogen content did not vary. Comment
Glucagon produces anorexia and weight loss in pregnant and nonpregnant rats, while weight loss is not as marked in the gestational animal. Blood ,ylllcose failPc1 to re-
838
Tyson,
Kinch,
and
Stevenson
July
15. I9G8
Am. J. Obst. & Gyner.
main elevated in pregnant animals while glucagon produced persistent hyperglycemia in the nonpregnant rat. A diabetic-like state was produced in the nonpregnant animal with polydypsia, hyperglycemia, and glycosuria. This is modified by pregnancy to include only polydypsia. Blood glucose might escape to the fetus in pregnancy as seen in lower maternal fasting blood glucose levels. The normal fasting values in late pregnancy in animals receiving glncagon may represent a decrease in available glucose stores resulting in increased catabolism. Retardation of fetal growth in the rat occurs under numerous circumstances. Knobil and Caton performed hypophysectomy on 12 day gestational rats and found a decrease in feta1 and pIacenta1 weights at birth. The effect was not due to a decreased food intake. He concluded that the fetal pituitary might control intrauterine growth in the rat. The administration of protamine-zincinsulin to maternal rats significantly reduced fetal and placental weights. Stillbirths and fetal anomalies were also increased.” lo The effect of hypophysectomy and insulin on fetal growth might represent a compromise in placental function with changes in placental perfusion and metabolism adversely affecting intrauterine development.
Glucagon affects fetal growth in the rat. Some have attributed this to an increase in protein catabolism. l1 Glucagon does increase the basal metabolic rate,12 but this is a modest rise. Our results suggest that glucagon affects fetal growth independent of decreased food intake. Since glucagon is beta cytotropic,13 its effect may be mediated through an augmented insulin release and a state of hyperinsulinism. Glucose would therefore be utilized by the maternal tissues, reducing the amount available for placental and fetal use. Glucagon appears to affect placental glycogen stores. No direct evidence is available at present to support this effect. It is felt that the decreased placental concentration may be secondary to maternal hepatic glycogen depletion. Pregnancy is a catabolic state for the maternal organism providing as much glucose as necessary for the growing fetus. This is achieved by the mobilization and metabolism of lipid and protein depots. When food intake alone is decreased, the fetus suffers a reduction in weight. There is a corresponding decrease in placental weight. Regular daily injections of glucagon to maternal rats result in the birth of offspring of decreased weight.
REFERENCES
Love, E. J., Kinch, R. A. H., and Stevenson, I. A. F.: AM. J. OBST. & GYNEC. 80: 536, i960. 2. Harding, P. G. R., Kinch, R. A. H., and Stevenson, J. A. F.: Diabetes 11: 321, 1962. 3. Sokal, J.: Am. J. Med. 41: 331, 1966. N.: 1. Biol. Chem. 153: 375, 1944. 4. Nelson. M.: J. Biol. Chem. 195: 19, 1952. 5. Somog$i, J. E.: Unpublished data, 1962. 6. Tyson, J. A., and Bloom, W.: Endocrinology 7. Russell, 58: 83, 1956. a. Knob& E., and Caton, W. E.: Endocrinology 53: 198, 1953. 1.
9.
10.
11.
12. 13.
Lichtenstein, H., Guest, G. M., and Warkany, J.: Proc. Sot. Exper. Biol. & Med. 78: 398, 1961. Love, E. J., Kinch, R. A. H., and Stevenson, J. A. F.: Proc. Canad. Fed. Biol. SC. IV: 40, 1961. Holloway, S., Stevenson, J, A. F., and Kinch, R. A. H.: Canad. J. Physiol. & Pharmacol. 43: 473, 1965. Salter, J., and Best, C. H.: Nature 180: 1124, 1957. Samols, E., Marri, G., and Marks, V. A.: Diabetes 15: 855, 1966.