Effects of pregnancy and ovarian steroids on fatty acid synthesis and uptake in Syrian hamsters ANITA
J. BHATIA
AND
Neuroscience and Behavior University of Massachusetts,
GEORGE
N. WADE
Program and Department Amherst, Massachusetts
BHATIA, ANITA J., AND GEORGEN. WADE. Effects ofpregnancy and ovarian steroids on fatty acid synthesis and uptake in Syrian hamsters. Am. J. Physiol. 260 (Regulatory Integrative Comp. Physiol. 29): R153-R158, 1991.-The effects of pregnancy and ovarian steroids on the in vivo distribution of newly synthesized fatty acids (incorporation of tritium from 3Hz0 into fatty acid) in Syrian hamsters (Mesocricetus auratus) were examined. During late, but not early, gestation hamsters had reduced levels of newly synthesized fatty acids in heart, liver, uterus, and white adipose tissues (parametrial and inguinal fat pads). Treatment of ovariectomized hamsters with estradiol + progesterone significantly decreased fatty acid synthesis-uptake in heart, liver, and inguinal white adipose tissue. Treatment with either estradiol or progesterone alone was without significant effect in any tissue. Pretreatment of hamsters with Triton WR-1339 (tyloxapol), an inhibitor of lipoprotein lipase activity and tissue triglyceride uptake, abolished the effects of estradiol + progesterone in white adipose tissue and heart but not in liver. Thus hamsters lose body fat during pregnancy in part because of decreased de novo lipogenesis. The effect of pregnancy on lipogenesis is mimicked by treatment with estradiol + progesterone but not by either hormone alone. Furthermore, it appears that the liver is the principal site of estradiol + progesterone action on lipogenesis in Syrian hamsters. estradiol;
progesterone;
lipogenesis
GONADAL STEROIDSAFFECT the ingestion,
distribution, storage, and expenditure of metabolic fuels (31, 32). Energy metabolism and regulatory behaviors vary with estrous and menstrual cycles as well as after gonadectomy and steroid replacement (6, 16, 23, 27, 33). In addition, significant alterations in energy balance occur during pregnancy (24, 25, 28, 33) when ovarian steroid titers, especially progesterone, are elevated (12, 15, 17). Pregnancy typically consists of two metabolic phases (3, 14). The first phase occurs during the initial twothirds of pregnancy and is characterized by maternal hyperphagia and increased fat deposition. In rats this increase in fat storage is reflected by a fivefold increase in fatty acid synthesis/uptake in liver and parametrial white adipose tissue (PWAT) (8). The second phase is catabolic in relation to the mother and persists until delivery. During this second phase, food intake remains elevated but fat storage declines and fat mobilization increases (3, 14). During late gestation rats exhibit decreased (in liver) or similar (in PWAT) levels of fatty acid synthesis/uptake compared with nonpregnant animals (8).
of Psychology, 01003
Unlike rats, Syrian hamsters do not increase food intake during pregnancy, but instead rely on their body fat stores as an energy source for fetal and maternal growth (10, 33). This results in an -40% loss of body fat in pregnant hamsters (33). Although pregnant rats and hamsters exhibit opposite changes in energy balance and body fat storage, the effects of pregnancy on food intake and body fat content are mimicked by treatment with estradiol + progesterone in both species. Ovariectomized (OVX) hamsters treated with estradiol + progesterone have decreased carcass lipid compared with animals treated with estradiol alone without significant differences in daily food intake (5). On the other hand, OVX rats treated with estradiol + progesterone have increased body fat and food intake compared with animals treated with estradiol alone (11, 30). Treatment of OVX hamsters or rats with estradiol alone reverses or prevents ovariectomy-induced weight and fat gains (5, 7, 18, 19, 27)
We examined the effects of pregnancy and ovarian steroids on the in vivo distribution of newly synthesized fatty acids in Syrian hamsters. A subsequent experiment used the nonionic detergent Triton WR-1339 to determine whether the effects of ovarian steroids on tissue fatty acid synthesis/uptake were due to changes in in situ lipogenesis or in uptake of fatty acids synthesized elsewhere. METHODS Subjects
Female Syrian hamsters (initial body weights 90-100 g) of the Lak:LVG strain were obtained from Charles River Breeding Laboratories, Wilmington, MA. All hamsters were housed individually in wire-bottom, stainless steel cages for at least 1 wk before the start of any experiments. Tap water and Purina Laboratory Rodent Chow (no. 5001) were available ad libitum. A 16:8 h lightdark cycle was maintained in all experiments with lights on at 0700 h in experiments 1, 3, and 4. Experiment 2 was run as two separate replicates with lights on at 0900 h in the first replicate and at 0700 h in the second replicate. Room temperature was controlled at 22 t 2°C. Surgery
Ovariectomies were done via bilateral, dorsolateral incisions irrespective of cycle day under methoxyflurane
0363-6119/91 $1.50 Copyright 0 1991 the American Physiological Society
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R154
OVARIAN
STEROIDS
(Metofane, Pitman-Moore) or pentobarbital sodium (80 mg/kg) anesthesia. Hormones were administered via subcutaneous implants containing crystalline 17P-estradiol (Sigma) in l.O-cm lengths of Silastic tubing (no. 602235; 1.47 mm ID, 1.96 mm OD; Dow Corning), crystalline progesterone (Sigma) in 2.5cm lengths of Silastic tubing, and 1.0 and 2.5 cm empty blanks placed in the interscapular region. Estradiol implants of this type induce plasma estradiol levels of 98 t 5 pg/ml (26), whereas a single progesterone capsule induces plasma progesterone levels of 10 t 2 rig/ml (26). These estradiol and progesterone levels are in the physiological range for estrouscycling Syrian hamsters on the second day of diestrus and early proestrus, respectively (2, 15, 17). All implants were placed in 0.9% saline at room temperature with benzalkonium chloride (Zephrin Chloride) overnight to sterilize and prime them before implantation. Lipogenesis
Fatty acid synthesis/uptake was measured (7, 29) in heart, liver, uterus, and inguinal white adipose tissue (IWAT) in experiments l-4 and also in PWAT in only experiment 1. In experiment 1, in which assays were done on uterine tissue of pregnant hamsters, the conceptus was not separated from the uterine tissue in Day 4 pregnant hamsters, whereas the conceptus was carefully dissected from the uterine tissue in Day 12 pregnant hamsters. Animals were given intraperitoneal injections of 1 mCi 3H20 between 0.5 and 2 h after lights on. One hour later they were given an overdose (-50 mg) of pentobarbital sodium, a blood sample was taken via cardiac puncture, and tissues were dissected and weighed. Samples were saponified in ethanolic KOH for 2 h, acidified, and extracted three times with petroleum ether. Combined extracts were washed three times with distilled water and dried. Radioactivity was counted in a toluene-based scintillation fluid. Incorporation of hydrogen into fatty acid was calculated by dividing the activity of the sample by the specific activity of plasma water. Note that this method does not discriminate between tissue lipids synthesized in situ and those synthesized elsewhere and taken up from circulation. In experiment 4, hamsters were anesthetized with methoxyflurane and given 0.35 ml Triton WR-1339 (tyloxapol, Sigma) (10% w-t/v01 in 0.85% saline) by cardiac puncture 0.5 h before injection of 3H20. Statistical
Analyses
All results are expressed as means t SE. The data were initially analyzed using a one-way Brown-Forsythe analysis of variance (ANOVA, two-tailed), which does not assume homogeneity of variance, or a mixed-model ANOVA (two-tailed) as appropriate with stage of pregnancy or hormone treatment as a between-groups variable and days or weeks as a within-subjects variable. Post hoc analyses using Welch t tests (P < 0.05) after BrownForsythe ANOVAs or Tukey’s multiple comparison tests (P < 0.05) after mixed-model ANOVAs were done only if the relevant main or interaction statistic was significant at P < 0.05.
AND
LIPOGENESIS
Procedures Experiment 1. Hamsters were weighed daily, and food intake (spillage and pouching accounted for) was measured. Estrous cycles were monitored by the method of Orsini (20) between 0700 and 1000 h daily. The day of the postovulatory vaginal discharge was designated as day 1 of the 4-day estrous cycle. Hamsters were then left unmated (Unmated; n=7) or were mated with experienced stud males. Males were placed in the female’s cage 1 h before lights out on the evening of day 4 of the estrous cycle and were removed within 1 h of lights on the following day. Mated animals were killed on either day 4 of pregnancy (n=7; Day 4) or day 12 of pregnancy (n=7; Day 12). One-half of the Unmated group was killed with the Day 4 hamsters, and one-half was killed with the Day 12 hamsters. All the hamsters in the Unmated group were combined into a single group for the statistical analyses of lipogenesis. For the analyses of the body weight and food intake data Day 4 hamsters and Day 12 hamsters were compared with their respective unmated control groups. Unmated hamsters were killed on the morning of day 3 of the estrous cycle. Experiments 2 and 3. Hamsters were divided into four groups matched for baseline body weights. All animals were OVX and given two subcutaneous Silastic implants in the interscapular region. In experiment 2, hamsters received two empty implants (Blank; n=13), an estradiol capsule and a blank (E; n=15), a progesterone capsule and a blank (P; n=ll), or an estradiol and a progesterone capsule (E + P; n=15). In experiment 3 hamsters received three blanks (Blank; n=9), an estradiol capsule and two blanks (E; n=8), an estradiol capsule, a progesterone capsule, and a blank (E + 1P; n=ll), or an estradiol and two progesterone capsules (E + 2P; n=ll). Because a single progesterone implant of this kind induces plasma progesterone levels of 10 t 2 rig/ml (26), two progesterone implants of this kind should induce progesterone plasma levels of -20 rig/ml, which are in the physiological range of pregnant hamsters (15, 17). Body weight and food intake were measured for 2 wk after surgery. All hamsters were then killed and tissues were assayed. Experiment 4. Hamsters were divided into three groups matched for baseline body weights. All animals were OVX and given three subcutaneous Silastic implants in the interscapular region. Hamsters received blanks (Blank; n=lO), an estradiol capsule and two blanks (E; n=8), or an estradiol and two progesterone capsules (E + 2P; n=lO). Body weight and food intake were measured for 2 wk after surgery. All hamsters were then treated with Triton WR-1339 followed by 3Hz0 and then killed. RESULTS
Experiment
1: Pregnancy
As reported previously (33), body weight had increased by day 12, but not day 4 of pregnancy. Food intake did not change during pregnancy (data not shown). Levels of newly synthesized fatty acids were reduced significantly by late pregnancy in heart [F(2,11) = 8.3; P < 0.011, liver [F(2,7) = 5.7; P < 0.051, uterus [F(2,15) = 7.4; P < 0.011, IWAT [F(2,12) = 5.5; P < 0.051, and
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OVARIAN
STEROIDS
AND
PWAT [F(2,11) = 4.5; P < 0.051 (Fig. 1). Although the Day 4 group did not differ from the Unmated group, the Day 12 hamsters had significantly lowered levels of fatty
estradiol and progesterone (E + 1P and E + 2P groups) exhibited an initial increase in weight gain followed by weight losses and accompanying decreases in food intake. Estradiol alone decreased weight gain without affecting food intake. Hormone treatments significantly decreased fatty acid synthesis/uptake in heart [F( 3,16) = 4.1; P < 0.051, liver [F(3,16) = 6.0; P c O.OOl], and IWAT [F(3,17) = 5.7; P c 0.011, but not uterus [F(3,23) = 1.0; P > 0.41 (Fig. 3). Both the E +lP and E + 2P hamsters, which did not differ in fatty acid synthesis/uptake levels in any tissue examined in this experiment, had decreased levels of fatty acid in liver, IWAT, and heart compared with the Blank hamsters. The E + 2P hamsters also had decreased fatty acid synthesis/uptake in both liver and IWAT, whereas the E + 1P had decreased levels only in liver compared with the E hamsters. Hamsters treated with estradiol alone had similar amounts of tritium incorporation into fatty acid in heart, liver, and IWAT compared with the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(3,27) = 0.2; P > 0.81. There were significant effects of hormone treatment on the weights of fat pads examined [IWAT: F(3,39) = 6.9, P < 0.005; and RWAT: F(3,28) = 11.6, P < 0.0051. The IWAT and RWAT weights did not differ among groups of hamsters treated with estradiol alone (E) or with progesterone (E + 1P and E + 2P), but both the RWAT and IWAT weights of hamsters treated with estradiol alone or estradiol + progesterone were significantly lower compared with those of the Blank group (data not shown).
acid in all tissues compared with both the Unmated and the Day 4 hamsters. There was no effect of stage of pregnancy on the specific activity of plasma water [F(2,9) = 1.0; P > 0.41. Experiment
2: Effects of Estradiol
and Progesterone
Significant changes were seen over time in weight gain [weeks x hormone interaction: F(3,50) = 20.2; P < O.OOl] and food intake [weeks x hormone interaction: F(3,50) = 19.2; P c O.OOl] (Table 1). As reported previously (5), estradiol alone decreased weight gain and progesterone alone increased weight gain compared with Blank hamsters. Hamsters treated with estradiol + progesterone exhibited a transient increase in weight gain during the first week after surgery followed by weight losses. During the first week after surgery E hamsters and during the second week the E + P hamsters had decreased food intakes. Hormone treatments significantly affected levels of newly synthesized fatty acid in heart [F(3,28) = 6.3; P < 0.0051, liver [F( 3,27) = 9.5; P c O.OOOS], and IWAT [F(3,27) = 3.4; P c 0.051, but not uterus [F(3,45) = 2.0; P > 0.051 (Fig. 2). Treatment with E + P decreased fatty acid synthesis/uptake in heart, liver, and IWAT compared with the Blank and P hamsters. The E + P hamsters also had lowered fatty acid levels in liver and IWAT compared with the E hamsters. Hamsters treated with estradiol alone had decreased levels of fatty acid in liver, IWAT, and heart compared with the P hamsters, but not the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(3,37) = 1.4; P >
Experiment
3: Progesterone
Dose
Significant changes were seen over time in weight gain [weeks x hormone interaction: F(3,35) = 3.9; P < 0.011 and food intake [weeks x hormone interaction: F(3,35) = 4.7; P < 0.011 (Table 1). Hamsters treated with both c;.
5.
/-Liver
Parametrial
d
6
WAT
4: Triton
WR-1339
Significant changes were seen over time in weight gain [weeks X hormone interaction: F(2,28) = 23.3; P < O.OOl] and food intake [weeks x hormone interaction: F(2,28) = 18.8; P < O.OOl] (Table 1). Treatment with estradiol alone decreased both weight gain and weekly food intake. Hamsters treated with both estradiol and p rogesterone exhibited an initial increase in weight gain followed by weight losses and decreased food intake. Unlike in experiments 2 and 3, the weight gains of hamsters treated with estradiol + progesterone still exceeded the mean weight gains of
0.21.
Experiment
R155
LIPOGENESIS
fhguinal
WAT
a
T
a
b
5 .0
Heart t
2.5
FIG. 1. In vivo tritium incorporation (from “HZO) into fatty acid in liver, parametrial white adipose tissue (WAT), inguinal WAT, uterus, and heart in unmated, 4-day pregnant, or 12-day pregnant hamsters. Bars with different letters are significantly different (P c 0.05).
a u
Unmated
q
Pregnant,
Day
4
Pregnant,
Day
12
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R156
OVARIAN
STEROIDS
TABLE 1. Weight gain and food intake of hormone- treated ovariectomized Syrian hamsters
AND
LIPOGENESIS
I
I-
iver
cl Blank RI
Week
Weight gain
1
Food intake Experiment
Blank E P E+P
3.6+1.3ab 0.2+1.2b 7.Ok1.3” 6.5kl.O”
6.OkO.8” 0.3*0.7b 9.Ok1.2” 9.8tl.O”
Blank E E+2P
3.4kl.l” -1.5kO.8” 9.8kl.l”
Weight
b
T
k
6
b
T
Heart
3 11.8U.9” 0.7*4.3b -0.5+2.7b 3.9&2.1b
5.0
87.Ok2.7” 77.1+3.2b 65.0+3.5b 72.2+3.gb
t 2.5
4 1 l.Ok6.6” -3.2H.2b 4.1U.9”
Liver t
E+ZP
76.5k3.2” 68.722.7” 81.122.8” 55.7+3.3b
Values are means * SE and are expressed in g/wk. E, estradiol; P, progesterone. See text for details. Different letters indicate statistically significant differences (Tukey’s multiple comparison tests, P < 0.05) within experiments. ‘I
WAT
a
lzzl E+lP
n
Food intake
8.7+2.5b 0.2t1.2” 15.2+1.6b -3.121.7”
79.9t3.0 69.423.9 74.7k3.8 79.6k3.7 Experiment 73.9k2.4 67.3H.8 77.4k2.2
gain
2
2
71.7_+2.5ab 68.4+2.6b 77.7k2.5” 75.1*2. lab Experiment
Blank E E+lP E+2P
Week
lnguinal
E
t
a
lnguinal
WAT
FIG. 3. In vivo tritium incorporation (from 3HZO) into fatty acid in liver, inguinal WAT, uterus, and heart in ovariectomized hamsters that received 3 subcutaneous implants. Hamsters received empty implants (Blank), an estradiol and 2 empty implants (E), an estradiol and 1 progesterone implant (E + lP), or an estradiol and 2 progesterone implants (E + 2P). Bars with different letters are significantly different (P c 0.05).
with estradiol alone had similar amounts of tritium incorporation into fatty acid in liver and plasma compared with the Blank hamsters. Both the E + 1P and the E hamsters had increased levels of fatty acid in uterus compared with the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(2,24) = 2.1; P > 0.11. Heart Ezl P RI E
DISCUSSION
4
During pregnancy, hamsters lose a substantial portion of their body fat stores (24, 33). Changes in de novo lEi!l E+P T E lipogenesis contribute to this reduction in body fat. Syn2 2 thesis/uptake of fatty acids is unchanged during early pregnancy and is significantly decreased by day 12 of gestation. Thus it appears that one reason hamsters lose s body fat during pregnancy is that they do not undergo an FIG. 2. In vivo tritium incorporation (from “HZO) into fatty acid in anabolic, fat-storing phase that other species exhibit durliver, inguinal WAT, uterus, and heart in ovariectomized hamsters that ing the first two-thirds of gestation. They then exhibit a received subcutaneous implants. Hamsters received empty implants significant decrease in de novo lipogenesis during late (Blank) or were treated with progesterone (P), estradiol (E), or estradiol pregnancy. and progesterone (E + P). Bars with different letters are significantly Treatment with estradiol + progesterone mimicked the different (P < 0.05). effects of pregnancy on fatty acid synthesis/uptake (exthe E hamsters during the second week after implantation. periments 2 and 3). Treatment of OVX hamsters with The body weights of the E + 2P (112.6 t 1.9 g) and the estradiol + progesterone decreased fatty acid synthesis/ E (105.8 t 2.0 g) hamsters at the end of the second week uptake in heart, liver, and inguinal white adipose tissue were similar and both were decreased compared with the compared with OVX controls and OVX hamsters treated body weights of the Blank hamsters (121.2 t 2.3 g). with estradiol or progesterone alone. The differences obHormone treatments significantly affected the levels of served among groups treated with estradiol alone comtritium incorporation into fatty acid after Triton WRpared with groups treated with estradiol + progesterone 1339 administration in liver [F(2,23) = 7.5; P < O.OOS] are not due to differences in food intake, body weight, or and uterus [F(2,21) = 3.4; P < 0.051 but not in plasma weight gain. [F(2,21) = 2.1; P > 0.11, heart [F(2,23) = 0.7; P > 0.501, Treatment with progesterone alone had no effect on or IWAT [F(2,23) = 1.0; P > 0.301 (Fig. 4). The E + 2P fatty acid synthesis/uptake on any of the tissues examhamsters had lower levels of fatty acid in liver compared ined. This finding is consistent with the fact that physwith both the Blank and the E hamsters. Hamsters treated iological doses of progesterone do not affect body fat c/l
t
a
ah
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OVARIAN
AND
a f
R157
LIPOGENESIS
WAT
lnguinal
I Liver
STEROIDS
0
a
Blank
Isi E E+2P
n
Heart m l-b
FIG. 4. In vivo tritium incorporation (from “HPO) into fatty acid in liver, inguinal WAT, uterus, heart, and plasma in ovariectomized hamsters that received 3 subcutaneous implants. Hamsters received empty implants (Blank), an estradiol and 2 empty implants (E), or an estradiol and 2 progesterone implants (E + 2P). All animals were given an intracardial injection of Triton WR-1339 0.5 h before treatment with 3HZ0. Bars with different letters are significantly different (P < 0.05).
Plasma 1 .o T
II
T
0.5
-
content in OVX Syrian hamsters (5). On the other hand, chronic treatment with estradiol reduces body weight and fat content in OVX hamsters (5, 23), and this decrease in body fat stores could be due in part to estradiol-induced reductions in fatty acid synthesis/uptake (Figs. 2 and 3). Finally, the fact that estradiol + progesterone given together decrease lipogenesis more than estradiol (Figs. 2 and 3) supports our previous finding that chronic treatment with both steroids decreases body fat stores more than estradiol alone (5). The effects of estradiol + progesterone on levels of newly synthesized fatty acids in white adipose tissue and heart were abolished when triglyceride uptake was prevented by pretreatment with Triton WR-1339 (Fig. 4). This indicates that ovarian steroids do not affect in situ lipogenesis in these tissues. Rather the hormone-induced reductions in adipose tissue and cardiac fatty acids seem to be due to decreased uptake of circulating lipids synthesized elsewhere. This reduced uptake could be due to changes in tissue lipoprotein lipase activity or to changes in levels of circulating lipids. The only available data suggest that estradiol treatment has no significant effect on lipoprotein lipase activity in hamster white adipose tissue (7). On the other hand, estradiol treatment decreases circulating triglycerides (7)) and treatment with estradiol + progesterone tends to lower circulating levels of newly synthesized fatty acids (Fig. 4). Thus, although we cannot rule out a role for changes in lipoprotein lipase activity, ovarian steroids probably reduce tissue fatty acid uptake mainly by lowering circulating lipids. It is likely that ovarian steroids reduce circulating lipids via actions in the liver. The liver accounts for a substantial portion of whole body lipogenesis in Syrian hamsters (29). The actions of estradiol + progesterone on hepatic lipogenesis were unaffected by pretreatment with Triton WR1339, indicating that ovarian steroids decrease in situ lipogenesis in hamster liver. Thus estradiol + progesterone treatment appears to decrease adipose lipid stores in hamsters by inhibiting hepatic lipogenesis, thereby reducing the amount of circulating lipid available for uptake
and storage in white adipose tissue. This contrasts with the situation in rats in which estradiol decreases body fat stores despite increased hepatic lipogenesis (7). In rats, estradiol may act mainly on white adipose tissue to reduce lipoprotein lipase activity and in situ lipogenesis and to stimulate lipolysis (4, 13). It is also conceivable that an increased transfer of fatty acids to the fetuses could contribute to the decreased storage of newly synthesized lipids in late-pregnant hamsters. However, the present data do not shed any light on this possibility. Finally, treatment with Triton WR-1339 revealed that treatment with estradiol + progesterone stimulates in situ lipogenesis in uterus (Fig. 4). In hamsters not treated with Triton WR-1339, this enhanced in situ lipogenesis may be masked by decreases in uptake of circulating fatty acids (Fig. 4, cf. Figs. 2 and 3). We are grateful to Jay Alexander and Robin Lempicki for expert technical assistance. This work was supported by National Institutes of Health Research Grants NS-10873 and DK-32976 and by National Institute of Mental Health Research Scientist Development Award MH-00321. Address for reprint requests: A. J. Bhatia, Dept. of Psychology, University of Massachusetts, Amherst, MA 01003. Received
8 June
1990; accepted
in final
form
31 August
1990.
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AND
LIPOGENESIS
Anim. Cure Panel 11: 193-206, 1961. 21. OTWAY, S., AND D. S. ROBINSON. The effect of a non-ionic detergent (Triton WR-1339) on the removal of triglyceride fatty acids fom the blood of the rat. J. Physiol. Land. 170: 309-319, 1967. 22. OTWAY, S., AND D. S. ROBINSON. The significance of changes in tissue clearing-factor lipase activity in relation to the lipaemia of pregnancy. Biochem. J. 106: 677-682, 1968. 23. SCHNEIDER, J. E., L. A. PALMER, AND G. N. WADE. Effects of estrous cycles and ovarian steroids on body weight and energy expenditure in Syrian hamsters. Physiol. Behuv. 38: 119-126, 1986. 24. SCHNEIDER, J. E., AND G. N. WADE. Body composition, food intake, and brown fat thermogenesis in pregnant Djungarian hamsters. Am. J. Physiol. 253 (Regulatory Integrative Comp. Physiol. 22): R314R320,1987. 25. STEINGRIMSDOTTIR, L., M. R. C. GREENWOOD, AND L. A. BRASEL. Effect of pregnancy, lactation and high fat diet on adipose tissue in Osborne-Mendel rats. J. Nutr. 110: 600- 609, 1980. 26. TAKEDA, A., AND W. W. LEAVITT. Temporal effects of progesterone domination on estrogen and oxytocin receptors in hamster uterus. J. Steroid Biochem. 25: 219-224, 1986. M. F., AND R. A. GORSKI. The effects of ovarian steroids 27. TARTTELIN, on food and water intake and body weight in the female rat. Acta Endocrinol. 73: 551-568, 1973. 28. TOMA, R. B., AND D. A. KELLY. Regional differences in dietary intake and fluid consumption during pregnancy. Nutr. Rep. Int. 36: 847-850,1987. 29. TRAYHURN, P. Fatty acid synthesis in brown adipose tissue in relation to whole body synthesis in the cold-acclimated golden hamster (Mesocricetus auratus). Biochim. Biophys. Acta 620: 10-17, 1980. 30. WADE, G. N. Some effects of ovarian hormones on food intake and body weight in female rats. J. Comp. Physiol. Psychol. 88: 183-193, 1975. 31. WADE, G. N. Sex hormones, regulatory behaviors, and body weight. In: Advances in the Study of Behavior, edited by J. S. Rosenblatt, R. A. Hinde, E. Shaw, and C. G. Beer. New York: Academic, 1976, vol. 6, p. 201-279. effects on food intake and 32. WADE, G. N., AND J. M. GRAY. Gonadal adiposity: a metabolic hypothesis. Physiol. Behuv. 22: 583-593, 1979. AND P. TRAYHURN. Energy balance and 33. WADE, G. N., G. JENNINGS, brown adipose tissue thermogenesis during pregnancy in Syrian hamsters. Am. J. Physiol. 250 (Regulatory Integrative Comp. Physiol. 19): R845-R850,1986.
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J. BHATIA
AND
Neuroscience and Behavior University of Massachusetts,
GEORGE
N. WADE
Program and Department Amherst, Massachusetts
BHATIA, ANITA J., AND GEORGEN. WADE. Effects ofpregnancy and ovarian steroids on fatty acid synthesis and uptake in Syrian hamsters. Am. J. Physiol. 260 (Regulatory Integrative Comp. Physiol. 29): R153-R158, 1991.-The effects of pregnancy and ovarian steroids on the in vivo distribution of newly synthesized fatty acids (incorporation of tritium from 3Hz0 into fatty acid) in Syrian hamsters (Mesocricetus auratus) were examined. During late, but not early, gestation hamsters had reduced levels of newly synthesized fatty acids in heart, liver, uterus, and white adipose tissues (parametrial and inguinal fat pads). Treatment of ovariectomized hamsters with estradiol + progesterone significantly decreased fatty acid synthesis-uptake in heart, liver, and inguinal white adipose tissue. Treatment with either estradiol or progesterone alone was without significant effect in any tissue. Pretreatment of hamsters with Triton WR-1339 (tyloxapol), an inhibitor of lipoprotein lipase activity and tissue triglyceride uptake, abolished the effects of estradiol + progesterone in white adipose tissue and heart but not in liver. Thus hamsters lose body fat during pregnancy in part because of decreased de novo lipogenesis. The effect of pregnancy on lipogenesis is mimicked by treatment with estradiol + progesterone but not by either hormone alone. Furthermore, it appears that the liver is the principal site of estradiol + progesterone action on lipogenesis in Syrian hamsters. estradiol;
progesterone;
lipogenesis
GONADAL STEROIDSAFFECT the ingestion,
distribution, storage, and expenditure of metabolic fuels (31, 32). Energy metabolism and regulatory behaviors vary with estrous and menstrual cycles as well as after gonadectomy and steroid replacement (6, 16, 23, 27, 33). In addition, significant alterations in energy balance occur during pregnancy (24, 25, 28, 33) when ovarian steroid titers, especially progesterone, are elevated (12, 15, 17). Pregnancy typically consists of two metabolic phases (3, 14). The first phase occurs during the initial twothirds of pregnancy and is characterized by maternal hyperphagia and increased fat deposition. In rats this increase in fat storage is reflected by a fivefold increase in fatty acid synthesis/uptake in liver and parametrial white adipose tissue (PWAT) (8). The second phase is catabolic in relation to the mother and persists until delivery. During this second phase, food intake remains elevated but fat storage declines and fat mobilization increases (3, 14). During late gestation rats exhibit decreased (in liver) or similar (in PWAT) levels of fatty acid synthesis/uptake compared with nonpregnant animals (8).
of Psychology, 01003
Unlike rats, Syrian hamsters do not increase food intake during pregnancy, but instead rely on their body fat stores as an energy source for fetal and maternal growth (10, 33). This results in an -40% loss of body fat in pregnant hamsters (33). Although pregnant rats and hamsters exhibit opposite changes in energy balance and body fat storage, the effects of pregnancy on food intake and body fat content are mimicked by treatment with estradiol + progesterone in both species. Ovariectomized (OVX) hamsters treated with estradiol + progesterone have decreased carcass lipid compared with animals treated with estradiol alone without significant differences in daily food intake (5). On the other hand, OVX rats treated with estradiol + progesterone have increased body fat and food intake compared with animals treated with estradiol alone (11, 30). Treatment of OVX hamsters or rats with estradiol alone reverses or prevents ovariectomy-induced weight and fat gains (5, 7, 18, 19, 27)
We examined the effects of pregnancy and ovarian steroids on the in vivo distribution of newly synthesized fatty acids in Syrian hamsters. A subsequent experiment used the nonionic detergent Triton WR-1339 to determine whether the effects of ovarian steroids on tissue fatty acid synthesis/uptake were due to changes in in situ lipogenesis or in uptake of fatty acids synthesized elsewhere. METHODS Subjects
Female Syrian hamsters (initial body weights 90-100 g) of the Lak:LVG strain were obtained from Charles River Breeding Laboratories, Wilmington, MA. All hamsters were housed individually in wire-bottom, stainless steel cages for at least 1 wk before the start of any experiments. Tap water and Purina Laboratory Rodent Chow (no. 5001) were available ad libitum. A 16:8 h lightdark cycle was maintained in all experiments with lights on at 0700 h in experiments 1, 3, and 4. Experiment 2 was run as two separate replicates with lights on at 0900 h in the first replicate and at 0700 h in the second replicate. Room temperature was controlled at 22 t 2°C. Surgery
Ovariectomies were done via bilateral, dorsolateral incisions irrespective of cycle day under methoxyflurane
0363-6119/91 $1.50 Copyright 0 1991 the American Physiological Society
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OVARIAN
STEROIDS
(Metofane, Pitman-Moore) or pentobarbital sodium (80 mg/kg) anesthesia. Hormones were administered via subcutaneous implants containing crystalline 17P-estradiol (Sigma) in l.O-cm lengths of Silastic tubing (no. 602235; 1.47 mm ID, 1.96 mm OD; Dow Corning), crystalline progesterone (Sigma) in 2.5cm lengths of Silastic tubing, and 1.0 and 2.5 cm empty blanks placed in the interscapular region. Estradiol implants of this type induce plasma estradiol levels of 98 t 5 pg/ml (26), whereas a single progesterone capsule induces plasma progesterone levels of 10 t 2 rig/ml (26). These estradiol and progesterone levels are in the physiological range for estrouscycling Syrian hamsters on the second day of diestrus and early proestrus, respectively (2, 15, 17). All implants were placed in 0.9% saline at room temperature with benzalkonium chloride (Zephrin Chloride) overnight to sterilize and prime them before implantation. Lipogenesis
Fatty acid synthesis/uptake was measured (7, 29) in heart, liver, uterus, and inguinal white adipose tissue (IWAT) in experiments l-4 and also in PWAT in only experiment 1. In experiment 1, in which assays were done on uterine tissue of pregnant hamsters, the conceptus was not separated from the uterine tissue in Day 4 pregnant hamsters, whereas the conceptus was carefully dissected from the uterine tissue in Day 12 pregnant hamsters. Animals were given intraperitoneal injections of 1 mCi 3H20 between 0.5 and 2 h after lights on. One hour later they were given an overdose (-50 mg) of pentobarbital sodium, a blood sample was taken via cardiac puncture, and tissues were dissected and weighed. Samples were saponified in ethanolic KOH for 2 h, acidified, and extracted three times with petroleum ether. Combined extracts were washed three times with distilled water and dried. Radioactivity was counted in a toluene-based scintillation fluid. Incorporation of hydrogen into fatty acid was calculated by dividing the activity of the sample by the specific activity of plasma water. Note that this method does not discriminate between tissue lipids synthesized in situ and those synthesized elsewhere and taken up from circulation. In experiment 4, hamsters were anesthetized with methoxyflurane and given 0.35 ml Triton WR-1339 (tyloxapol, Sigma) (10% w-t/v01 in 0.85% saline) by cardiac puncture 0.5 h before injection of 3H20. Statistical
Analyses
All results are expressed as means t SE. The data were initially analyzed using a one-way Brown-Forsythe analysis of variance (ANOVA, two-tailed), which does not assume homogeneity of variance, or a mixed-model ANOVA (two-tailed) as appropriate with stage of pregnancy or hormone treatment as a between-groups variable and days or weeks as a within-subjects variable. Post hoc analyses using Welch t tests (P < 0.05) after BrownForsythe ANOVAs or Tukey’s multiple comparison tests (P < 0.05) after mixed-model ANOVAs were done only if the relevant main or interaction statistic was significant at P < 0.05.
AND
LIPOGENESIS
Procedures Experiment 1. Hamsters were weighed daily, and food intake (spillage and pouching accounted for) was measured. Estrous cycles were monitored by the method of Orsini (20) between 0700 and 1000 h daily. The day of the postovulatory vaginal discharge was designated as day 1 of the 4-day estrous cycle. Hamsters were then left unmated (Unmated; n=7) or were mated with experienced stud males. Males were placed in the female’s cage 1 h before lights out on the evening of day 4 of the estrous cycle and were removed within 1 h of lights on the following day. Mated animals were killed on either day 4 of pregnancy (n=7; Day 4) or day 12 of pregnancy (n=7; Day 12). One-half of the Unmated group was killed with the Day 4 hamsters, and one-half was killed with the Day 12 hamsters. All the hamsters in the Unmated group were combined into a single group for the statistical analyses of lipogenesis. For the analyses of the body weight and food intake data Day 4 hamsters and Day 12 hamsters were compared with their respective unmated control groups. Unmated hamsters were killed on the morning of day 3 of the estrous cycle. Experiments 2 and 3. Hamsters were divided into four groups matched for baseline body weights. All animals were OVX and given two subcutaneous Silastic implants in the interscapular region. In experiment 2, hamsters received two empty implants (Blank; n=13), an estradiol capsule and a blank (E; n=15), a progesterone capsule and a blank (P; n=ll), or an estradiol and a progesterone capsule (E + P; n=15). In experiment 3 hamsters received three blanks (Blank; n=9), an estradiol capsule and two blanks (E; n=8), an estradiol capsule, a progesterone capsule, and a blank (E + 1P; n=ll), or an estradiol and two progesterone capsules (E + 2P; n=ll). Because a single progesterone implant of this kind induces plasma progesterone levels of 10 t 2 rig/ml (26), two progesterone implants of this kind should induce progesterone plasma levels of -20 rig/ml, which are in the physiological range of pregnant hamsters (15, 17). Body weight and food intake were measured for 2 wk after surgery. All hamsters were then killed and tissues were assayed. Experiment 4. Hamsters were divided into three groups matched for baseline body weights. All animals were OVX and given three subcutaneous Silastic implants in the interscapular region. Hamsters received blanks (Blank; n=lO), an estradiol capsule and two blanks (E; n=8), or an estradiol and two progesterone capsules (E + 2P; n=lO). Body weight and food intake were measured for 2 wk after surgery. All hamsters were then treated with Triton WR-1339 followed by 3Hz0 and then killed. RESULTS
Experiment
1: Pregnancy
As reported previously (33), body weight had increased by day 12, but not day 4 of pregnancy. Food intake did not change during pregnancy (data not shown). Levels of newly synthesized fatty acids were reduced significantly by late pregnancy in heart [F(2,11) = 8.3; P < 0.011, liver [F(2,7) = 5.7; P < 0.051, uterus [F(2,15) = 7.4; P < 0.011, IWAT [F(2,12) = 5.5; P < 0.051, and
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OVARIAN
STEROIDS
AND
PWAT [F(2,11) = 4.5; P < 0.051 (Fig. 1). Although the Day 4 group did not differ from the Unmated group, the Day 12 hamsters had significantly lowered levels of fatty
estradiol and progesterone (E + 1P and E + 2P groups) exhibited an initial increase in weight gain followed by weight losses and accompanying decreases in food intake. Estradiol alone decreased weight gain without affecting food intake. Hormone treatments significantly decreased fatty acid synthesis/uptake in heart [F( 3,16) = 4.1; P < 0.051, liver [F(3,16) = 6.0; P c O.OOl], and IWAT [F(3,17) = 5.7; P c 0.011, but not uterus [F(3,23) = 1.0; P > 0.41 (Fig. 3). Both the E +lP and E + 2P hamsters, which did not differ in fatty acid synthesis/uptake levels in any tissue examined in this experiment, had decreased levels of fatty acid in liver, IWAT, and heart compared with the Blank hamsters. The E + 2P hamsters also had decreased fatty acid synthesis/uptake in both liver and IWAT, whereas the E + 1P had decreased levels only in liver compared with the E hamsters. Hamsters treated with estradiol alone had similar amounts of tritium incorporation into fatty acid in heart, liver, and IWAT compared with the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(3,27) = 0.2; P > 0.81. There were significant effects of hormone treatment on the weights of fat pads examined [IWAT: F(3,39) = 6.9, P < 0.005; and RWAT: F(3,28) = 11.6, P < 0.0051. The IWAT and RWAT weights did not differ among groups of hamsters treated with estradiol alone (E) or with progesterone (E + 1P and E + 2P), but both the RWAT and IWAT weights of hamsters treated with estradiol alone or estradiol + progesterone were significantly lower compared with those of the Blank group (data not shown).
acid in all tissues compared with both the Unmated and the Day 4 hamsters. There was no effect of stage of pregnancy on the specific activity of plasma water [F(2,9) = 1.0; P > 0.41. Experiment
2: Effects of Estradiol
and Progesterone
Significant changes were seen over time in weight gain [weeks x hormone interaction: F(3,50) = 20.2; P < O.OOl] and food intake [weeks x hormone interaction: F(3,50) = 19.2; P c O.OOl] (Table 1). As reported previously (5), estradiol alone decreased weight gain and progesterone alone increased weight gain compared with Blank hamsters. Hamsters treated with estradiol + progesterone exhibited a transient increase in weight gain during the first week after surgery followed by weight losses. During the first week after surgery E hamsters and during the second week the E + P hamsters had decreased food intakes. Hormone treatments significantly affected levels of newly synthesized fatty acid in heart [F(3,28) = 6.3; P < 0.0051, liver [F( 3,27) = 9.5; P c O.OOOS], and IWAT [F(3,27) = 3.4; P c 0.051, but not uterus [F(3,45) = 2.0; P > 0.051 (Fig. 2). Treatment with E + P decreased fatty acid synthesis/uptake in heart, liver, and IWAT compared with the Blank and P hamsters. The E + P hamsters also had lowered fatty acid levels in liver and IWAT compared with the E hamsters. Hamsters treated with estradiol alone had decreased levels of fatty acid in liver, IWAT, and heart compared with the P hamsters, but not the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(3,37) = 1.4; P >
Experiment
3: Progesterone
Dose
Significant changes were seen over time in weight gain [weeks x hormone interaction: F(3,35) = 3.9; P < 0.011 and food intake [weeks x hormone interaction: F(3,35) = 4.7; P < 0.011 (Table 1). Hamsters treated with both c;.
5.
/-Liver
Parametrial
d
6
WAT
4: Triton
WR-1339
Significant changes were seen over time in weight gain [weeks X hormone interaction: F(2,28) = 23.3; P < O.OOl] and food intake [weeks x hormone interaction: F(2,28) = 18.8; P < O.OOl] (Table 1). Treatment with estradiol alone decreased both weight gain and weekly food intake. Hamsters treated with both estradiol and p rogesterone exhibited an initial increase in weight gain followed by weight losses and decreased food intake. Unlike in experiments 2 and 3, the weight gains of hamsters treated with estradiol + progesterone still exceeded the mean weight gains of
0.21.
Experiment
R155
LIPOGENESIS
fhguinal
WAT
a
T
a
b
5 .0
Heart t
2.5
FIG. 1. In vivo tritium incorporation (from “HZO) into fatty acid in liver, parametrial white adipose tissue (WAT), inguinal WAT, uterus, and heart in unmated, 4-day pregnant, or 12-day pregnant hamsters. Bars with different letters are significantly different (P c 0.05).
a u
Unmated
q
Pregnant,
Day
4
Pregnant,
Day
12
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R156
OVARIAN
STEROIDS
TABLE 1. Weight gain and food intake of hormone- treated ovariectomized Syrian hamsters
AND
LIPOGENESIS
I
I-
iver
cl Blank RI
Week
Weight gain
1
Food intake Experiment
Blank E P E+P
3.6+1.3ab 0.2+1.2b 7.Ok1.3” 6.5kl.O”
6.OkO.8” 0.3*0.7b 9.Ok1.2” 9.8tl.O”
Blank E E+2P
3.4kl.l” -1.5kO.8” 9.8kl.l”
Weight
b
T
k
6
b
T
Heart
3 11.8U.9” 0.7*4.3b -0.5+2.7b 3.9&2.1b
5.0
87.Ok2.7” 77.1+3.2b 65.0+3.5b 72.2+3.gb
t 2.5
4 1 l.Ok6.6” -3.2H.2b 4.1U.9”
Liver t
E+ZP
76.5k3.2” 68.722.7” 81.122.8” 55.7+3.3b
Values are means * SE and are expressed in g/wk. E, estradiol; P, progesterone. See text for details. Different letters indicate statistically significant differences (Tukey’s multiple comparison tests, P < 0.05) within experiments. ‘I
WAT
a
lzzl E+lP
n
Food intake
8.7+2.5b 0.2t1.2” 15.2+1.6b -3.121.7”
79.9t3.0 69.423.9 74.7k3.8 79.6k3.7 Experiment 73.9k2.4 67.3H.8 77.4k2.2
gain
2
2
71.7_+2.5ab 68.4+2.6b 77.7k2.5” 75.1*2. lab Experiment
Blank E E+lP E+2P
Week
lnguinal
E
t
a
lnguinal
WAT
FIG. 3. In vivo tritium incorporation (from 3HZO) into fatty acid in liver, inguinal WAT, uterus, and heart in ovariectomized hamsters that received 3 subcutaneous implants. Hamsters received empty implants (Blank), an estradiol and 2 empty implants (E), an estradiol and 1 progesterone implant (E + lP), or an estradiol and 2 progesterone implants (E + 2P). Bars with different letters are significantly different (P c 0.05).
with estradiol alone had similar amounts of tritium incorporation into fatty acid in liver and plasma compared with the Blank hamsters. Both the E + 1P and the E hamsters had increased levels of fatty acid in uterus compared with the Blank hamsters. There was no effect of hormone treatment on the specific activity of plasma water [F(2,24) = 2.1; P > 0.11. Heart Ezl P RI E
DISCUSSION
4
During pregnancy, hamsters lose a substantial portion of their body fat stores (24, 33). Changes in de novo lEi!l E+P T E lipogenesis contribute to this reduction in body fat. Syn2 2 thesis/uptake of fatty acids is unchanged during early pregnancy and is significantly decreased by day 12 of gestation. Thus it appears that one reason hamsters lose s body fat during pregnancy is that they do not undergo an FIG. 2. In vivo tritium incorporation (from “HZO) into fatty acid in anabolic, fat-storing phase that other species exhibit durliver, inguinal WAT, uterus, and heart in ovariectomized hamsters that ing the first two-thirds of gestation. They then exhibit a received subcutaneous implants. Hamsters received empty implants significant decrease in de novo lipogenesis during late (Blank) or were treated with progesterone (P), estradiol (E), or estradiol pregnancy. and progesterone (E + P). Bars with different letters are significantly Treatment with estradiol + progesterone mimicked the different (P < 0.05). effects of pregnancy on fatty acid synthesis/uptake (exthe E hamsters during the second week after implantation. periments 2 and 3). Treatment of OVX hamsters with The body weights of the E + 2P (112.6 t 1.9 g) and the estradiol + progesterone decreased fatty acid synthesis/ E (105.8 t 2.0 g) hamsters at the end of the second week uptake in heart, liver, and inguinal white adipose tissue were similar and both were decreased compared with the compared with OVX controls and OVX hamsters treated body weights of the Blank hamsters (121.2 t 2.3 g). with estradiol or progesterone alone. The differences obHormone treatments significantly affected the levels of served among groups treated with estradiol alone comtritium incorporation into fatty acid after Triton WRpared with groups treated with estradiol + progesterone 1339 administration in liver [F(2,23) = 7.5; P < O.OOS] are not due to differences in food intake, body weight, or and uterus [F(2,21) = 3.4; P < 0.051 but not in plasma weight gain. [F(2,21) = 2.1; P > 0.11, heart [F(2,23) = 0.7; P > 0.501, Treatment with progesterone alone had no effect on or IWAT [F(2,23) = 1.0; P > 0.301 (Fig. 4). The E + 2P fatty acid synthesis/uptake on any of the tissues examhamsters had lower levels of fatty acid in liver compared ined. This finding is consistent with the fact that physwith both the Blank and the E hamsters. Hamsters treated iological doses of progesterone do not affect body fat c/l
t
a
ah
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OVARIAN
AND
a f
R157
LIPOGENESIS
WAT
lnguinal
I Liver
STEROIDS
0
a
Blank
Isi E E+2P
n
Heart m l-b
FIG. 4. In vivo tritium incorporation (from “HPO) into fatty acid in liver, inguinal WAT, uterus, heart, and plasma in ovariectomized hamsters that received 3 subcutaneous implants. Hamsters received empty implants (Blank), an estradiol and 2 empty implants (E), or an estradiol and 2 progesterone implants (E + 2P). All animals were given an intracardial injection of Triton WR-1339 0.5 h before treatment with 3HZ0. Bars with different letters are significantly different (P < 0.05).
Plasma 1 .o T
II
T
0.5
-
content in OVX Syrian hamsters (5). On the other hand, chronic treatment with estradiol reduces body weight and fat content in OVX hamsters (5, 23), and this decrease in body fat stores could be due in part to estradiol-induced reductions in fatty acid synthesis/uptake (Figs. 2 and 3). Finally, the fact that estradiol + progesterone given together decrease lipogenesis more than estradiol (Figs. 2 and 3) supports our previous finding that chronic treatment with both steroids decreases body fat stores more than estradiol alone (5). The effects of estradiol + progesterone on levels of newly synthesized fatty acids in white adipose tissue and heart were abolished when triglyceride uptake was prevented by pretreatment with Triton WR-1339 (Fig. 4). This indicates that ovarian steroids do not affect in situ lipogenesis in these tissues. Rather the hormone-induced reductions in adipose tissue and cardiac fatty acids seem to be due to decreased uptake of circulating lipids synthesized elsewhere. This reduced uptake could be due to changes in tissue lipoprotein lipase activity or to changes in levels of circulating lipids. The only available data suggest that estradiol treatment has no significant effect on lipoprotein lipase activity in hamster white adipose tissue (7). On the other hand, estradiol treatment decreases circulating triglycerides (7)) and treatment with estradiol + progesterone tends to lower circulating levels of newly synthesized fatty acids (Fig. 4). Thus, although we cannot rule out a role for changes in lipoprotein lipase activity, ovarian steroids probably reduce tissue fatty acid uptake mainly by lowering circulating lipids. It is likely that ovarian steroids reduce circulating lipids via actions in the liver. The liver accounts for a substantial portion of whole body lipogenesis in Syrian hamsters (29). The actions of estradiol + progesterone on hepatic lipogenesis were unaffected by pretreatment with Triton WR1339, indicating that ovarian steroids decrease in situ lipogenesis in hamster liver. Thus estradiol + progesterone treatment appears to decrease adipose lipid stores in hamsters by inhibiting hepatic lipogenesis, thereby reducing the amount of circulating lipid available for uptake
and storage in white adipose tissue. This contrasts with the situation in rats in which estradiol decreases body fat stores despite increased hepatic lipogenesis (7). In rats, estradiol may act mainly on white adipose tissue to reduce lipoprotein lipase activity and in situ lipogenesis and to stimulate lipolysis (4, 13). It is also conceivable that an increased transfer of fatty acids to the fetuses could contribute to the decreased storage of newly synthesized lipids in late-pregnant hamsters. However, the present data do not shed any light on this possibility. Finally, treatment with Triton WR-1339 revealed that treatment with estradiol + progesterone stimulates in situ lipogenesis in uterus (Fig. 4). In hamsters not treated with Triton WR-1339, this enhanced in situ lipogenesis may be masked by decreases in uptake of circulating fatty acids (Fig. 4, cf. Figs. 2 and 3). We are grateful to Jay Alexander and Robin Lempicki for expert technical assistance. This work was supported by National Institutes of Health Research Grants NS-10873 and DK-32976 and by National Institute of Mental Health Research Scientist Development Award MH-00321. Address for reprint requests: A. J. Bhatia, Dept. of Psychology, University of Massachusetts, Amherst, MA 01003. Received
8 June
1990; accepted
in final
form
31 August
1990.
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R158
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OVARIAN
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