Ovarian modulation of lipoprotein lipase activity in white adipose tissue of ground squirrels

Golden-mantled ground squirrels were ovariectomized (OVX) or Sham-OVX during the weight gain phase of the circannual body weight cycle. Other squirrels, OVX or Sham-OVX during the weight loss phase, were subcutaneously implanted with estradiol-filled or empty Silastic capsules. The mass of several fat pads as well as adipose tissue lipoprotein lipase (LPL) activity were determined at autopsy. Ovariectomy at either phase of the annual cycle was without effect on body weight. However, LPL activity of the parametrial fat pad was increased in OVX as compared to Sham-OVX squirrels. Fourteen days of estradiol treatment during the weight loss phase decreased the mass and LPL activity of the retroperitoneal fat depot but did not affect these parameters in perirenal adipose tissue. Although estradiol exerts different or opposite effects on body mass and food intake of rats and ground squirrels, ovariectomy and estrogen treatment affect LPL activity in a similar fashion in both species.     

Food intake and adipose tissue lipoprotein lipase activity after hypothalamic estradiol benzoate implants in rats

Unilateral implants of estradiol benzoate in the ventromedial hypothalamus (VMH) reduced food intake in ovariectomized rats. The implants did not produce cornification of the vaginal epithelium. Furthermore, the reduction in food intake was observed in the absence of changes in adipose tissue lipoprotein lipase activity or cytoplasmic progestin receptor levels. These results suggest that, while estradiol may normally act at both central and peripheral sites to affect food intake and body weight, estrogenic stimulation of just the VMH may be sufficient to reduce food intake in ovariectomized rats.     

Adipose tissue lipoprotein lipase activity in rats maintained at a reduced body weight

Male rats fed a cellulose-diluted diet maintained a reduced body weight. Adipose tissue lipoprotein lipase (LPL) activity decreased after two days of cellulose feeding, but was not different from chow-fed control levels with weight stabilized at 90% or 70% of the control group. Plasma triglyceride concentration decreased with weight loss and remained depressed with stabilized reduced weight. Regaining lost weight had no effect on LPL activity when compared with chow-fed controls or with levels obtained for the weight-reduced group. However, plasma triglyceride concentration returned to chow-fed control levels with weight gain. The disparity between these results and those obtained in obese human beings lends support to the hypothesis that the increase in adipose tissue LPL activity in weight-reduced obese human beings is indicative of a defect in regulation of adipose tissue metabolism.     

Gonadal effects on food intake and adiposity: a metabolic hypothesis.

Ovarian and testicular steroids have important effects on body weight and composition in rats. Estradiol and testosterone decrease adiposity, while progesterone increases carcass fat content. These hormone-induced changes in body weight and composition are accompanied by changes in food intake and voluntary exercise, suggesting that the hormones induce behavioral changes which alter body weight and adiposity. However, several lines of evidence indicate that these behavioral changes are neither necessary nor sufficient to produce the hormone-induced body weight shifts. Rather, peripheral metabolic effects of gonadal steroids may be of primary importance in the control of fat disposition. Steroid effects on triglyceride clearance from circulation, along with changes in hepatic synthesis, may in turn alter the availability of triglycerides as an oxidizable fuel, contributing to the changes in food intake. From this perspective, estradiol- and progesterone-induced changes in food intake are viewed as consequences, rather than causes, of changes in fat metabolism. It is suggested that during naturally-occurring reproductive states gonadal steroids interact with other hormones, such as prolactin, to partition available triglycerides among tissues which oxidize, excrete or store long-chain fatty acids (e.g., striated muscle, mammary gland, or adipose tissue, respectively).     

Copulation affects body weight but not food intake or dietary self-selection in male rats

The mechanisms responsible for copulation-induced changes in body weight were investigated using adult male rats. Animals that copulated two or three times a week for 6 weeks gained less weight than sexually inactive controls. The reductions in body weight gain were not associated with changes in total caloric intake or the intake of specific nutrients. Adipose tissue lipoprotein lipase activity was not affected by sexual activity. Based upon these results and previous observations, we suggest that copulation-induced reductions in body weight may not be mediated solely by testicular testosterone.     

Food intake, body weight and lordosis in male and female mongolian gerbils: effects of ovarian steroids

The effects of gonadectomy and ovarian hormone treatment on food intake, body weight, and lordosis in male and female Mongolian gerbils were examined. In female gerbils, a significant decrease in food intake and body weight was observed after ovariectomy, with estradiol benzoate (1, 10, or 100 micrograms/day) increasing food intake in a dose dependent fashion. However, the dose of estrogen (1 microgram) that restored food intake and body weight to control levels in ovariectomized animals was lower than that required to elicit maximal sexual receptivity. Progesterone, when given in conjunction with estrogen, significantly facilitated the effect of estrogen on food intake without further altering body weight. In male gerbils, castration produced a significant but transient increase in body weight and a delayed increase in food intake. Unlike female gerbils, male gerbils exhibited no significant alterations in food intake, body weight, or lordosis in response to treatment with ovarian steroids. The present results are compared to those obtained in other species.     

Effects of selective estrogen receptor agonists on food intake and body weight gain in rats

Ovariectomized (OVX) rats eat more and gain weight more rapidly than sham-operated (SO) rats and estradiol (E(2)) treatment attenuates food intake and body weight gain in OVX rats. Studies were designed to test the hypothesis that the alpha subtype of the estrogen receptor (ERalpha) mediates the attenuating effects of E(2) on food intake and body weight gain while the beta subtype (ERbeta) mediates opposing actions that lead to increased food intake and body weight gain. Female rats were SO or OVX and treated daily with vehicle (dimethylsulfoxide, DMSO) or E(2) (10 microg/day), or the ERalpha-selective agonist, 4,4',4'-(4-propyl-[1H]-pyrazole-1,3,5-triyl)trisphenol (PPT, 0.5 mg/day), or the ERbeta-selective agonist, 2,3-bis(4-hyroxyphenyl)-propionitrile (DPN, 0.5 mg/day) for 14 days. Total food intake was significantly reduced by E(2) and PPT, but not DPN. Total body weight gain was significantly increased in OVX rats compared to SO rats and treatment with E(2) or PPT, but not DPN, significantly decreased total body weight gain to levels that were not significantly different from SO rats. A dose-response study of PPT indicated that at 0.25 mg/day, PPT significantly reduced total 21-day food intake and body weight gain and, at 0.13 and 0.06 mg/day, PPT significantly reduced total body weight gain compared to OVX rats without significantly reducing total food intake. A dose-response study of DPN indicated that none of the three doses of DPN significantly altered total 21-day food intake or total body weight gain. These results suggest ERalpha mediates the attenuating effects of estrogens on food intake and body weight gain while ERbeta has no effect on these variables.     

Effects of ovariectomy and estradiol on body weight and food intake in gold thioglucose-treated mice

Two experiments investigated the effects of ovariectomy and estradiol replacement on the body weight and food intake of mice that had previously been treated with either gold thioglucose or saline. Ovariectomy and estradiol benzoate injections altered food intake in gold thioglucose-treated mice as much as in saline controls. Ovariectomy increased body weight in saline controls but it was without effect on the body weight of gold thioglucose-treated mice.     

Sex differences in the activational effects of gonadal hormones on food intake and body weight

Estrogens have been shown to decrease, and androgens to increase body weight (BWt) of guinea pigs (GPs). The magnitude of the BWt sex difference shown by intact adult GPs is due primarily to these concurrent, or activational, effects of gonadal steroids. However, a small but significant sex difference in BWt persists in animals gonadectomized at birth, indicating that early hormonal exposure may permanently influence certain steroid sensitive weight regulatory mechanisms in the two sexes. Three experiments were therefore designed to investigate the short term effects of estradiol and testosterone on food intake (FI) and BWt of gonadectomized adult male and female GPs. In the first experiment, GPs gonadectomized in adulthood were given a single injection of 6 micrograms estradiol benzoate (EB). Although EB treatment reduced FI and BWt of both females and males, significantly larger reductions occurred in females. In the second experiment, GPs gonadectomized at birth received treatments of oil or 2 micrograms EB for 7 days. EB treatment also produced significantly larger effects on FI and BWt in the neonatally gonadectomized females. The third experiment involved GPs gonadectomized as adults who were injected with either oil or 1 mg/day testosterone propionate in oil (TP) for 32 days. Compared to changes in oil injected controls, TP produced significantly larger increases in male BWt than female BWt. Therefore, although GPs show only minor sex differences in BWt which might relate to prenatal gonadal hormonal exposure, significant sex differences remain in their responsiveness to the activational effects of gonadal steroids on FI and BWt in adulthood.     

Effects of stereoisomers of estradiol on food intake, body weight and hoarding behavior in female rats

The effects of 17-alpha and 17-beta estradiol on food intake, body weight and hoarding behavior in ovariectomised rats were investigated. For five days, ten animals received subcutaneous injections of both isomers (10 micrograms/kg/day) in a counterbalanced design. Hoarding tests were conducted on the last three days of each 5-day injection period. 17-Alpha estradiol significantly reduced food intake but was without effect on body weight. 17-Beta estradiol reduced food intake significantly more than the alpha form and also significantly reduced body weight. These differential effects suggest that stereoisomers of estradiol may be acting on separate regulatory systems. The treatments did not change hoarding activity compared to pre-treatment levels.     

Aldosterone-stimulated feeding and weight gain: Interactions with estrogen?

The effects of combined adrenalectomy-ovariectomy and steroid replacement on food intake, spillage, body weight, skeletal growth, and fluid retention were investigated in rats that were fed freely or held to a controlled allotment. The stimulation of feeding and weight gain by aldosterone was not dependent upon the presence of estradiol. Likewise, the suppression of food intake and weight gain brought about by estradiol was not influenced by aldosterone, leading us to conclude that the effects of the two hormones are independent and additive, not interactive. Estradiol and aldosterone each significantly altered the rate of food spillage and in opposite directions. There was a marked reduction in the extent to which estradiol influenced body weight in the controlled feeding situation. Accompanying this was a differential effect of estradiol on body growth. Depending upon feeding condition, estradiol either retarded (free-feeding) or accelerated (restricted) skeletal growth. Aldosterone's stimulation of weight gain was nearly proportional across feeding conditions, and it did not influence body growth.     

Ovarian influences on food intake and body weight regulation in lactating rats

In the following experiments, an attempt was made to determine the role of the ovary in the control of food intake and body weight regulation during lactation. In the first study, it was found that concentrations of estradiol benzoate effective in suppressing food intake and body weight in nonlactating animals were not effective during lactation. In the second experiment, ovariectomy during lactation was shown not to produce the usual increases in food intake and body weight or change in meal patterns known to occur after ovariectomy in the nonlactating rat. These results suggested that lactating animals behave the as though functionally ovariectomized and that the removal of the ovaries is of no additional consequence. The further observation that animals nursing small litters gained weight considerably more rapidly than animals nursing large litters led to the prediction that these animals would also be more responsive to the suppressive effects of EB. In the third study, EB in concentrations which are not effective in suppressing body weight in animals nursing large litters was found to suppress body weight in mothers with small litters. However, since these animals also showed a decline in milk yield, a number of alternative interpretations of these results were considered. These results, together with data concerning levels of ovarian hormones during gestation and lactation led to the hypothesis that pregnant and lactating animals undergo an elevation in body weight set-point, similar in magnitude and quality to elevations following ovariectomy in the nonlactating animal.     

Ovarian influences on body weight regulation in rats with lateral hypothalamic lesions

The effect of lateral hypothalamic lesions upon the level of maintained body weight was studied in gonadally intact and ovariectomized female rats. The body weight of both the gonadally intact and ovariectomized animals declined after lesioning; but, while the weight level of the ovariectomized animals remained approximately 10% below normal, the body weight of the intact group steadily approached that of nonlesioned controls. This result suggests that ovarian factors contribute to the smaller effect on body weight as reported by others for females with lateral hypothalamic lesions. Further support for this hypothesis was found in the observations that (1) the reduced effect of lateral hypothalamic lesions on body weight of gonadally intact females was associated with prolonged periods of diestrus and (2) the normal weight suppressing effects of estrogen were attenuated by lateral hypothalamic lesions in the ovariectomized animals.     

Gonadal hormones and behavioral regulation of body weight

Gonadal hormones have important effects on the behaviors that determine body weight in laboratory rats (i.e., eating, locomotor activity, and thermoregulatory behavior). These effects are most evident in the female where there are consistent, predictable changes in these behaviors which are correlated with fluctuations in plasma hormone levels during estrous cycles, puberty, pregnancy, or after gonadectomy and replacement therapy. Estradiol, which seems to be the principal ovarian steroid affecting body weight, may act directly on separate neural loci to: (a) inhibit food intake and (b) stimulate locomotor activity, possibly by lowering the set-point of a hypothalamic lipostat. Estradiol does not affect eating and running in prepubertal female rats, perhaps because of influences of pituitary hormone(s) at this age. Ovarian hormones also alter the taste preferences of rats and may be responsible for the changes in self-selection of dietary components during different reproductive states. Some implications of this research are discussed and possible directions for future research suggested.     

Estradiol and insulin: independent effects on eating and body weight in rats.

The effects of ovariectomy and estradiol replacement were determined in streptozotocin-diabetic female rats maintained on daily injections of protamine zinc insulin. Similar changes in food intake and body weight in these animals and in nondiabetic control animals indicate that the effects of estradiol on these measures are probably not dependent on changes in pancreatic insulin secretion. Acute and chronic insulin challenges in ovariectomized rats maintained on estradiol benzoate, nafoxidine or oil were also examined. The effects of insulin were not attenuated by prior estrogen conditioning, and there was no evidence of insulin resistance. These experiments suggest that the effects of estradiol on body weight and food intake in female rats are not dependent upon altered insulin levels nor attenuation of the effects of insulin. Estradiol may exert its influence on eating and body weight via separate and possibly more direct pathways. The data also are consistent with the suggestion that ovariectomy-induced and hypothalamic obesities are separate phenomena.     

Effect of voluntary wheel exercise on food intake,water intake,and body weight for C57BL/6J mice and mutations which differ in maximal body weight

The relations of voluntary wheel exercise, food intake, water intake, metabolic rate, and body weight were determined for mutant mice (bg, c^J, A^y, and ob) with C57BL/6J genetic background and also for littermate controls. Mutant groups high in body weight (A^y and ob) had lower metabolic rates, were less active, and ate more food than controls. The nonobese mutants (c^J, and bg) had higher metabolic rates than controls, but different behavioral mechanisms for control of body weight during voluntary wheel exercise. Voluntary wheel activity for the albino (c^J) mice was similar to that of controls, but food intake increased proportionally more for albinos than controls. Food intake was similar for beige (bg) mutants compared with controls, but the beige group engaged in less voluntary wheel activity than controls.     

Heredity and changes in body composition and adipose tissue metabolism after short-term exercise-training

Summary The purpose of the experiment was to investigate the genotype dependency of body composition and adipose tissue metabolism following short-term exercise-training. Six pairs of male, sedentary monozygotic twins took part in a 22 day ergocycle training program at 58% , with a mean exercise duration of 116 min · d^–1. Body weight, fat mass, percent body fat and were evaluated before and after the training program. From a suprailiac region fat biopsy, the following adipose tissue metabolic variables were evaluated: fat cell diameter, basal and epinephrine stimulated lipolysis, basal and insulin stimulated lipogenesis from glucose and heparin releasable lipoprotein lipase activity. The exercise-training program increased (p<0.01) and decreased (p<0.01) body weight, fat mass and percent body fat. Variation in response within twin pairs was not significantly different than response between pairs in the aforementioned variables. However, a significant within pair resemblance (p<0.01) for changes in fat free mass was observed. Adipose tissue metabolic indicators exhibited a large interindividual variation in response to exercise-training. Significant within twin pair resemblance was observed only for basal lipogenesis. Moreover, the non significant within twin pair resemblance for changes in body fat and adipose tissue metabolic indicators suggests that heredity is not a major factor influencing changes in body fat and adipose tissue indicators to short-term training resulting in negative energy balance. Changes in fat free mass were, however, closely coupled to the genotype.Supported by NSERC of Canada (G-0850 and A-8150), FCAC-Québec (EQ-1330) and Fitness Canada     

Effects of bulbectomy on hibernation,food intake and body weight in the european hamster,Cricetus cricetus

Bulbectomy was performed on European male wild hamsters in autumn, habitual phase of weight decline and entrance into hibernation. Total bulbectomy suppresses both nest building behavior and hibernation, and is followed by an immediate increase in food intake and obesity. The body weight curve of totally bulbectomized animals is in opposition of phase with that of the controls. Incomplete bulbectomy suppresses nest building behavior but hibernation is present with a diminution of periodic arousals. Hyperphagia starts in spring after the terminal arousal; it is similar to that of the total bulbectomized animals. Anosmic animals do not differ from the control animals.     

The ingestion of food and the recovery of body weight following fasting in the naive rat

The total food consumption of experimentally naive rats following 24, 48, 72, and 96 hr fasts was observed during the period of the recovery of body weight. The total amount of food consumed in excess of prefast food consumption was found in all groups to be equivalent to 24 hr intake and was, therefore, independent of degree of fast and body weight lost. Moreover, it was found that rats recover lost body weight following a fast even when intake is held to prefast levels. These findings suggest that the regulation of body weight may be under the control of mechanisms in addition to the control of food intake.