Effects of gonadal hormones on eating and body weight in mongolian gerbils (Meriones unguiculatus)

HORMONES

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Effects of Gonadal in Mongolian CHRISTIE

;78-i87 (i977)

Hormones on Eating and Body Weight Gerbils (Meriones unguiculatus) A. MAASS AND GEORGE N. WADE’

Department of Psychology, University of Massachusetts, Amherst, Massachusetts 01003 The effects of gonadal steroids on food intake and body weight were studied in Mongolian gerbils. Orchiectomy of adult male gerbils caused significant increases in body weight but had no detectable effect on food intake. Treatment with testosterone propionate or So-dihydrotestosterone propionate (100 &day) had no effect on food intake or body weight of orchiectomized males, but withdrawal of exogenous androgen treatment had the same effect as orchiectomy, increased body weight with no increase in food intake. Treatment with estradiol benzoate (EB; 2 &day) increased food intake and body weight of ovariectomized gerbils, but progesterone (1 mg/day) had no effect on these measures when given by itself. However, when progesterone was given concurrently with EB it synergized with the estrogen and further increased eating and body weight. These results are contrasted with previous work in other mammalian species.

Gonadal hormones influence food intake and body weight in males and females of a variety of mammalian species (Baile and Forbes, 1974; Kakolewski, Cox, and Valenstein, 1968; Wade, 1976). Gonadal effects on body weight of laboratory rats have received a great deal of experimental attention (see Wade, 1976, for a review), but data on other mammalian species are much less available. In the following experiments we have examined the effects of ovarian and testicular steroids on eating and body weight in Mongolian gerbils, Merimes unguiculutus, in an attempt to determine the extent to which principles derived from work in laboratory rats are applicable to another rodent species. The results indicate that gerbils are quite unlike rats in their eating and body weight responses to sex hormones. GENERAL

METHOD

Male and female Mongolian gerbils, approximately 14 weeks old, were purchased from Tumblebrook Farms (West Brookfield, Massachusetts). All animals were housed individually in Wahmann LC-75SA cages with wire-mesh bottoms. Purina Laboratory Chow and tap water were avail* To whom reprint requests should be addressed. 178 Copyright All rights

@ 1977 by Academic Ress, Inc. of reproduction in any form reserved.

ISSN 0018-506X

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able ad /i&turn. A 12:12-hr light-dark cycle (lights on at 0800 hr) was maintained throughout the experiments. Gerbils were permitted to acclimate to housing, food, water, and the light cycle for 3 weeks before baseline measurements were obtained. Measurements of body weight and of food consumption, including spillage, were obtained to the nearest 0.1 g every 3 days between 1200and 1300 hr throughout the experiments. During periods when exogenous hormone treatments were administered, animals received injections between 1300 and 1400 hr daily. EXPERIMENT

1 ORCHIECTOMY

In most species of mammals castration of males (orchiectomy) leads to a decrease in food intake and body weight gain. This pattern is certainly the case in laboratory rats (Gentry and Wade, 1976; Kakolewski et al., 1968). Golden hamsters, Mesocricetus auratus, are an interesting exception to this rule; orchiectomy increases body weight in hamsters (Kowalewski, 1969). In Experiment 1 we compared eating and body weight gains in orcheictomized and sham-operated gerbils. Method Gerbils were approximately 120 days of age at the beginning of the study. Baseline measurements of food intake and body weight were obtained for 9 days. Two groups of males were then matched on these measures. Fifteen animals were castrated and 10 received sham operations on Day 10 under methoxyflurane (Metofane) anesthesia. Measurements of food intake and body weight were obtained for 48 days postoperatively. Results Three of the orchiectomized gerbils and one sham-operated animal died during or as a result of surgical manipulations, leaving Ns of 12 and 9 in the two groups, respectively. Analyses were performed on individuals’ body weight gains between Day 6 of baseline and Day 48 of the postoperative period. Orchiectomy significantly increased body weight gains in gerbils, t (19) = 2.21, p < 0.05 (Fig. 1). By contrast, mean daily food intake was not systematically affected by this manipulation (Fig. 2). EXPERIMENT

2: ANDROGEN

TREATMENT

Androgen replacement therapy reverses the effects of orchiectomy on eating and body weight both in species such as rats, which lose weight after orchiectomy (Gentry and Wade, 1976), and in hamsters, which gain weight after orchiectomy (Zucker, Wade, and Ziegler, 1972). In Experiment 2 we attempted to reverse the body weight gains caused by orchiectomy in gerbils with treatments of testosterone propionate (TP) or of

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MAASS AND WADE EFFECT OF ORCHIECTOMY

ON BODY WEIGHT

SHAMS CASTRATES

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Effects of orchiectomy or sham-operation on

body

weights of male Mongolian

gerbils.

5o-dihydrotestosterone propionate (DHTP). In some peripheral androgen target tissues So-dihydrotestosterone is the physiologically active metabolite of testosterone (Mainwaring, 1977), but in rats DHTP is less effective than TP in stimulating food intake and body weight (Gentry and Wade, 1976). The testosterone dose we used (100 pg/day) is sufficient to restore normal levels of androgen-dependent scent marking in orchiectomized gerbils (Thiessen, Friend, and Lindzey, 1968). EFFECT OF ORCHIECTOMY ON FOOD INTAKE

a 07 B 36

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3-DAY FIG. 2.

gerbils.

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Effects of orchiectomy or sham-operation on food intake of male Mongolian

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WEIGHT

Method Eighteen male gerbils, castrated at 130 days of age, were permitted to recover under constant conditions for 8 weeks. Baseline measurements of food intake and body weight were then obtained for 9 days, and animals were assigned to one of three groups (N=6 each) matched on these measures. Animals received daily subcutaneous injections of either 100 pg of TP, 100 pg of DHTP, or sesame oil for 30 days. Both TP and DHTP were injected in 0.1 ml of oil vehicle. Food intake and body weight measurements were obtained throughout the hormone treatment period. Hormone administration was then discontinued, and the effects of withdrawal of the exogenous androgen treatment on eating and body weight were measured for an additional 48 days. Results Body weights of orchiectomized gerbils were not affected by either TP or DHTP (Fig. 3, center panel). However, following withdrawal of exogenous androgens, increases in body weight were observed in both hormone-treated groups. By Day 48 of the recovery phase (Fig. 3, last panel), TP-treated animals weighed significantly more than oil-injected controls, t (10) = 2.36, p < 0.05. Although DHTP-treated animals also exhibited elevated body weights on Day 48, they did not differ significantly from the oil-treated controls on this measure. A second analysis was performed on individuals’ body weight gains between Day 6 and Day 48 of the recovery phase. Withdrawal of either exogenous TP or DHTP produced significantly greater body weight gains over the recovery period EFFECT

OF ANDROGEN TREATMENT

ON BODY WEIGHT

HORMONE TREATMENT

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3-DAY FIG. 3. Effects propionate (DHTP, Mongolian gerbils.

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of testosterone propionate (TP, 100 &day), kdihydrotestosterone 100 &day), or sesame oil vehicle on body weights of orchiectomized

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than did withdrawal of the oil vehicle, t (10) = 4.77,~ < .OOl and t (10) = 3.93, p < -01, respectively. There was no evidence that withdrawal of exogenous TP had a significantly greater effect on body weight gain than did withdrawal of exogenous DHTP. Administration of either TP or DHTP to orchiectomized gerbils also failed to affect food intake over the injection period (Fig. 4, center panel). Furthermore, there were no statistically significant increases in this measure following withdrawal of exogenous TP or DHTP, although body weights were increasing in the previously hormone-treated groups (see the last panels of Fig. 3 and 4 for comparison). EXPERIMENT

3: ESTRADIOL

AND PROGESTERONE

TREATMENT

In rats estradiol-17P, whether of ovarian origin or supplied exogenously, depresses food intake and body weight. In estrous-cycling female rats food intake decreases at proestrus, just after the peak in estradiol secretion (Brobeck, Wheatland, and Strominger, 1947; Yoshinaga, Hawkins, and Stocker, 1969). Estrogen withdrawal by ovariectomy causes a transient increase in food intake and a lasting increase in body weight (Mook, Kenney, Roberts, Nussbaum, and Rodier, 1972); these effects are reversed by estradiol replacement therapy (Tarttelin and Gorski, 1973; Wade, 1975). Progesterone, by itself, has no effect on eating and body weight in ovariectomized rats, but it can inhibit the actions of estradiol when the two steroids are given concurrently (Wade, 1975). Progesterone is an extremely effective antiestrogen and antagonizes the effects of estradiol on a variety of behaviors (Morin, 1977). Estrogenic suppression of food intake and body weight is found in a EFFECT OF ANDROGEN TREATMENT ON FOOD INTAKE s

BPSELINE

HOWONE

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RECOVERY

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of testosteronepropionate(TP, lOOpg/day), Sol-dihydrotestosterone lOO&day), or sesame oil vehicle on food intake of orchiectomized

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variety of species. Decreases in eating or body weight at natural estrus or following estradiol treatment have been reported recently in guinea pigs (Czaja and Goy, 1975), mice (Blaustein, Gentry, Roy and Wade, 1976), hamsters (Morin and Fleming, in press.), sheep (Tarttelin, 1968), cattle (Forbes, 1971), and rhesus monkeys (Czaja, 1975; Czajaand Goy, 1975)to name a few. As a first step in studying sex hormone-body weight relations in female gerbils we had hoped to measure eating and body weight changes over the estrous cycle and following ovariectomy. Because we have been unable to obtain sufficient numbers of gerbils showing regular estrous cycles to perform these experiments, we have performed the second most logical experiment. We have treated ovariectomized gerbils with exogenous estradiol and progesterone and measured c-ating and body weight responses. Method

Twenty-four female gerbils were ovariectomized under methoxyflurane (Metofane) anesthesia at 130 days af age and maintained under constant conditions for 8 weeks. Baseline measurements of food intake and body weight were obtained for 9 days. At the end of this period, animals were assigned to one of four hormone treatment groups (ZV=6 each) matched for mean body weight and daily food intake. Animals received daily subcutaneous injections of either 2 pg of estradiol benzoate (EB), 1 mg of progesterone, 2 Fg of EB plus 1 mg of progesterone, or sesame oil vehicle. The hormones were injected in 0. I ml of oil. Measurements of food intake and body weight were obtained throughout the hormone replacement phase. At the end of this 30-day period, the effects of withdrawal of the exogenous ovarian hormone treatment on eating and body weight were measured for an additional 24 days. Results

Analyses were performed on individuals’ body weight gains over the 30 days of hormone treatment. Each of the hormone-treated groups was compared to the oil-injected controls. The results indicate that ovariectomized gerbils receiving exogenous EB and those receiving exogenous EB + progesterone gained significantly more weight over the hormone treatment phase than did animals receiving only oil injections, t (10) = 2.29,~ < .05 and t (10) = 3.63,~ < .Ol, respectively (Fig. 5, center panel). Injections of progesterone alone had no effect on body weight. Further, there was no evidence that progesterone antagonized the actions of EB. The EB + progesterone-treated gerbils gained slightly more weight over the hormone treatment phase than did gerbils receiving EB alone, but a comparison of EB- and EB + progesterone-injected groups was not statistically significant. Body weights returned to approximately control levels

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FIG. 5. Effects of estradiol benzoate (EB, 2 &day) and progesterone (P, I mg/day), alone or in combination (EB+ P), on body weights of ovariectomized Mongolian gerbils. Controls were injected with sesame oil vehicle.

by 3.5 weeks after cessation of hormone treatments (Fig. 5, last panel). Analyses were also performed on the change in daily food intake from the baseline period to the second half of the hormone treatment period (the period of peak weight gain). Both EB alone and EB + progesterone increased food intake during the latter half of the hormone treatment phase when compared with oil-treated controls, t (10) = 4.66, p < .OOl and t (10) = 7.35,~ < .OOl (Fig. 6). Treatment with progesterone alone did EFFECT OF OVARIAN HORMONES ON FOOD INTAKE HORMONE TREATMENT

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FIG. 6. Effects of estradiol benzoate (EB, ZLLg/day)and progesterone (P, 1 mg/day), alone or in combination (E+P), on food intake of ovariectomized Mongolian gerbils. Controls were injected with sesame oil vehicle.

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not affect food intake measures. Progesterone did not attenuate the EB effects. In fact, EB + progesterone treatment was more effective than EB alone in increasing food intake, t (10) = 3.86, p < .Ol. DISCUSSION

Taken together the results of these three experiments indicate that Mongolian gerbils are very different from any other species studied to date in their eating and body weight responses to gonadal steroids. These differences are particularly striking when the present results are contrasted with earlier work done in rats. Male rats eat less and display diminished body weight gains after orchiectomy (Gentry and Wade, 1976). Male gerbils increase body weight after orchiectomy, but they do not overeat during the accelerated weight gains (Experiment 1). Nyby (1974) has also found that orchiectomy increases body weight without stimulating food intake in gerbils. However, Nyby did find an increase in food hoarding in orchiectomized gerbils. The changes in body weight without accompanying food intake changes were somewhat unexpected. We have, however, seen similar changes in body weight despite unaltered food consumption in female rats when ovarian hormone levels are manipulated (Roy and Wade, 1977). Changes in locomotor activity and metabolic processes are probably sufficient to cause the body weight fluctuations. In rats TP treatment reverses the effects of orchiectomy on food intake and body weight (Gentry and Wade, 1976). Treatment with TP or DHTP had no effect on these measures in orchiectomized gerbils (Experiment 2), but withdrawal of exogenous TP or DHTP had the same effect as orchiectomy, increased weight gain without increased eating. This finding is most unusual. We are not aware of any other preparation in which repeated removal of a hormone produces behavioral/physiological effects which are not reversed by treatment with that hormone. On other occasions we have withdrawn androgens from male gerbils as many as three times (first time by orchiectomy, second and third times by cessation of TP treatment), and each time there has been a substantial weight gain (C. A. Maass, unpublished data). The significance of the weight gains following androgen withdrawal for wild-living gerbils is not known. It is possible that if gerbils display reduced reproductive activity (and androgen production) during winter, then the concomitant increases in body weight could provide increased fuel stores and insulation. Nyby (1974) has found that orchiectomyinduced body weight gains are accompanied by increases in lumbar fat weight and pelt weight. In female rats estradiol reduces eating and body weight; in ovariectomized gerbils these measures are increased by EB treatments (Experiment 3). On the other hand, progesterone alone has no effect on eating or

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body weight of ovariectomized rats (Wade, 1975) or gerbils (Experiment 3). In ovariectomized rats progesterone antagonizes the food intake- and body weight-suppressing actions of EB (Wade, 1975); in ovariectomized gerbils progesterone synergizes with estradiol to further stimulate eating and body weight. Again, this finding is most unusual. We are aware of no other species in which synergistic effects of estradiol and progesterone are seen on food intake and body weight. A second line of evidence is consistent with the possibility that estrogens stimulate eating and body weight in gerbils. The synthetic estrogen antagonist, MER-25, is not antiestrogenic with regard to eating and body weight in rats. In fact, MER-25 is fully estrogenic on these measures; it depresses both food intake and body weight in ovariectomized rats (Roy and Wade, 1976). Recently we have shown that MER-25 is also estrogenic for food intake and body weight in gerbils; it increases both measures in ovariectomized gerbils (Roy, Maass, and Wade, 1977). Thus, at least two compounds which are estrogenic and decrease food intake and body weight in rats also increase eating and body weight in gerbils. We do not know the anatomical sites or the biochemical mechanisms by which estradiol stimulates eating and body weight in gerbils. Recent data do indicate that the same brain regions where estradiol acts in rats also display high-affinity, saturable [3H]estradiol binding in gerbils (J. M. Gray & G. N. Wade, unpublished data). ACKNOWLEDGMENTS Supported by Research Grant NS 10873 and by Research Career Development Award NS 00090 from the National Institute of Neurological and Communicative Disorders and Stroke. Estradiol benzoate and progesterone were generously supplied by Dr. Irving Tabachnick of the Schering Corporation, Bloomfield, New Jersey. We are grateful to Jeffrey Blaustein, Susan Dudley, Thomas Gentry, Janet Gray, Edward Hirsch, Melinda Novak, and Edward Roy for helpful discussions.

REFERENCES Baile, C. A., and Forbes, J. M. (1974). Control of feed intake and regulation of energy balance in ruminants. Physiol. Rev. 54, 160-214. Blaustein, J. D., Gentry, R. T., Roy, E. J., and Wade, G. N. (1976). Ovarian influences on body weight and food intake in gold thioglucose-treated mice. Physiol. Behav. 17, 1027-1030. Brobeck, J. R., Wheatland, M., and Strominger, J. L. (1947). Variations in regulation of energy exchange associated with estrus, diestrus, and pseudopregnancy in rats. Endocrinology 40, 65-72. Czaja, J. A. (1975). Food rejection by female Rhesus monkeys during the menstrual cycle and early pregnancy. Physiol. Behav. 14, 579-587. Czaja, J. A., and Goy, R. W. (1975). Ovarian hormones and food intake in femaleguinea pigs and Rhesus monkeys. Norm. Behav. 6, 329-350. Forbes, J. M. (1971). Physiological changes affecting voluntary food intake in ruminants. Proc. Nutr. Sot. 30, 135-142.

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Gentry, R. T., and Wade, G. N. (1976). Androgenic control of food intake and body weight in male rats. J. Camp. Physiol. Psychol. 90, 18-25. Kakolewski, J. W., Cox, V. C., and Valenstein, E. S. (1968). Sex differences in body-weight changes following gonadectomy of rats. Psychol. Rep. 22, 547-554. Kowalewski, K. (1%9). Effect of pre-pubertal gonadectomy and treatment with sex hormones on body growth, weight of organs and skin collagen of hamsters. Acta Endocrinol.

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Mainwaring, W. I. P. (1977). The Mechanism ofAction ofAndrogens, Springer-Verlag, New York. Mook, D. G., Kenney, N. J., Roberts, S., Nussbaum, A. I., and Rodier, W. I., III. (1972). Ovarian-adrenal interactions in regulation of body weight by female rats. J. Comp. Physiol.

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Morin, L. P. (1977). Progesterone: Inhibition of rodent sexual behavior. Physiol. Behav. 18, 701-715. Morin, L. P., and Fleming, A. (1977). Variations in food intake and body weight with the estrous cycle, ovariectomy, and estradiol benzoate treatment in hamsters (Mesocricetus auratus). J. Comp. Physioi. Psychol., in press. Nyby, J. G. (1974). Physiological regulation of food hoarding in the Mongolian gerbil (Meriones unguicalatus). Doctoral dissertation, University of Texas, Austin. Roy, E. J., Maass, C. A., and Wade, G. N. (1977). Estrogenic effect of an antiestrogen on eating and body weight: Species comparison and central action. Physiol. Behav. 18, 137-140.

Roy, E. J., and Wade, G. N. (1976). Estrogenic effects of an antiestrogen, MER-25, on eating and body weight in rats. J. Comp. Physiol. Psychol. 90, 156-166. Roy, E. J., and Wade, G. N. (1977). Role of food intake in estradiol-induced body weight changes in female rats. Horm. Behav. 8, 265-274. Tarttelin, M. F. (1968). Cyclical variations in food and water intake of ewes. J. Physiol. 195, 29P-3 IP. Tarttelin, M. F., and Gorski, R. A. (1973). The effects of ovarian sterioids on food and water intake and body weight in the female rat. Acta Endocrinol. 72, 551-568. Thiessen, D. D., Friend, H. C., and Lindzey, G. (1968). Androgen control of territorial marking in the Mongolian gerbil. Science 160, 432-434. Wade, G. N. (1975). Some effects of ovarian hormones on food intake and body weight in female rats. J. Comp. Physiol. Psychol. 88, 183-193. Wade, G. N. (1976). Sex hormones, regulatory behaviors and body weight, In J. S. Rosenblatt, R. A. Hinde, E. Shaw, and C. G. Beer (Eds.), Advances in the Study of Behavior, Vol. 6. Academic Press, New York. Yoshinaga, K., Hawkins, R. W., and Stocker, J. F. (1969). Estrogen secretion by the rat ovary in vivo during the estrous cycle and pregnancy. Endocrinology 85, 103- 112. Zucker, I., Wade, G. N., and Ziegler, R. (1972). Sexual and hormonal influences on eating, taste preferences, and body weight of hamsters. Physiol. Behav. 8, 101-I I I.