Effects of testosterone on body weight and adipose tissue: role of aromatization

Changes in gene expression due to aging in the hypothalamus of mice

Aging generally affects food consumption and energy metabolism. Since the feeding center is located in the hypothalamus, it is a major target for understanding the mechanism of age-related changes in eating behavior and metabolism. To obtain insight into the age-related changes in gene expression in the hypothalamus, we investigated genes whose expression changes with age in the hypothalamus. A DNA microanalysis was performed using hypothalamus samples obtained from young (aged 24 weeks) and old male mice (aged 138 weeks). Gene Ontology (GO) analysis was performed using the identified differentially expressed genes. We observed that the expression of 377 probe sets was significantly altered with aging (177 were upregulated and 200 were downregulated in old mice). As a result of the GO analysis of these probe sets, 16 GO terms, including the neuropeptide signaling pathway, were obtained. Intriguingly, although the food intake in old mice was lower than that in young mice, we found that several neuropeptide genes, such as agouti-related neuropeptide (Agrp), neuropeptide Y (Npy), and pro-melanin-concentrating hormone (Pmch), all of which promote food intake, were upregulated in old mice. In conclusion, this suggests that the gene expression pattern in the hypothalamus is regulated to promote food intake.

The Roles of Androgens in Humans: Biology, Metabolic Regulation and Health

Androgens are an important and diverse group of steroid hormone molecular species. They play varied functional roles, such as the control of metabolic energy fate and partition, the maintenance of skeletal and body protein and integrity and the development of brain capabilities and behavioral setup (including those factors defining maleness). In addition, androgens are the precursors of estrogens, with which they share an extensive control of the reproductive mechanisms (in both sexes). In this review, the types of androgens, their functions and signaling are tabulated and described, including some less-known functions. The close interrelationship between corticosteroids and androgens is also analyzed, centered in the adrenal cortex, together with the main feedback control systems of the hypothalamic-hypophysis-gonads axis, and its modulation by the metabolic environment, sex, age and health. Testosterone (T) is singled out because of its high synthesis rate and turnover, but also because age-related hypogonadism is a key signal for the biologically planned early obsolescence of men, and the delayed onset of a faster rate of functional losses in women after menopause. The close collaboration of T with estradiol (E2) active in the maintenance of body metabolic systems is also presented Their parallel insufficiency has been directly related to the ravages of senescence and the metabolic syndrome constellation of disorders. The clinical use of T to correct hypoandrogenism helps maintain the functionality of core metabolism, limiting excess fat deposition, sarcopenia and cognoscitive frailty (part of these effects are due to the E2 generated from T). The effectiveness of using lipophilic T esters for T replacement treatments is analyzed in depth, and the main problems derived from their application are discussed.

Endogenous Androgens Diminish Food Intake and Activation of Orexin A Neurons in Response to Reduced Glucose Availability in Male Rats

Sex steroids modify feeding behavior and body weight regulation, and androgen reportedly augments food intake and body weight gain. To elucidate the role of endogenous androgens in the feeding regulation induced by reduced glucose availability, we examined the effect of gonadectomy (orchiectomy) on food intake and orexin A neuron’s activity in the lateral hypothalamic/perifornical area (LH/PFA) in response to reduced glucose availability (glucoprivation) induced by 2-deoxy-d-glucose (2DG) administration in male rats. Rats (7W) were bilaterally orchiectomized (ORX group) or sham operated (Sham group). Seventeen days after the surgery, food intake response to 2DG (400 mg/kg, i.v.) was measured for 4 h after the infusion. The same experiment was performed for the immunohistochemical examination of c-Fos-expressing orexin A neurons in the LH/PFA and c-Fos expression in the arcuate nucleus (Arc). Food intake induced by glucoprivation was greater in the ORX group than the Sham group, and the glucoprivation-induced food intake was inversely correlated with plasma testosterone concentration. Glucoprivation stimulated c-Fos expression of the orexin A neurons at the LH/PFA and c-Fos expression in the dorsomedial Arc. The number and percentage of c-Fos-expressing orexin A neurons in the LH/PFA and c-Fos expression in the dorsomedial Arc were significantly higher in the ORX group than the Sham group. This indicates that endogenous androgen, possibly testosterone, diminishes the food intake induced by reduced glucose availability, possibly via the attenuated activity of orexin A neuron in the LH/PFA and neurons in the dorsomedial Arc.

Ovarian hormones mediate running-induced changes in high fat diet choice patterns in female rats

Physical inactivity and increased consumption of energy dense, high fat (HF) foods often leads to a state of positive energy balance. Regular exercise can facilitate the maintenance of a healthy body weight and mediate changes in dietary selection. Past studies using a two-diet choice (chow vs. HF) and voluntary wheel running paradigm found that when a novel HF diet and wheel running are simultaneously introduced, male rats show complete and persistent HF diet avoidance whereas the majority of females show HF diet avoidance for a few days, but then revert to HF diet preference. Ovariectomy (OVX) appears to decrease preference for the HF diet bringing it closer to that of males. Given that estradiol but not progesterone mediates changes in food intake and energy balance, we hypothesized that estradiol signaling is required for the reversal of HF diet avoidance in female rats. Accordingly, Experiment 1 compared the persistency of running-induced HF diet avoidance in males, sham-operated females, and OVX rats with replacement of oil vehicle, estradiol benzoate (E), progesterone (P), or both (E + P). The number of wheel running rats that either avoided or preferred the HF diet varied with hormone treatment. The reversal of HF diet avoidance in running females and OVX E + P rats occurred more rapidly and frequently than male running rats. E + P but not E or P replaced OVX wheel running rats significantly reversed HF diet avoidance. OVX oil rats avoided HF diet to the same extent as male rats for the first 11 days of diet choice and then rapidly increased HF diet intake and began preferring it. This incomplete elimination of sex differences suggests that developmental factors or androgens might play a role in sustaining running-induced HF diet avoidance. Subsequently, Experiment 2 aimed to determine the role of androgens in the persistency of running-associated HF diet avoidance with sham-operated and orchiectomized (GDX) male rats. Both intact and GDX male running rats persistently avoided the HF diet to the same extent. Taken together, these results suggest that activational effects of ovarian hormones play a role in female specific running-induced changes in diet choice patterns. Furthermore, the activational effects of androgens are not required for the expression of HF diet avoidance in males.

Histological characteristics of the gonads of pig fetuses and their relationship with fetal anatomical measurements

The objective was to evaluate the histomorphometric characteristics of the testis and ovaries of pig fetuses at different gestational ages, as well as their correlation with some fetus measurements. Forty-four fetuses were separated for gender (male and female) and gestational age (50, 80 and 106days of gestation). After slaughter, fetuses had their body length, head and thoracic perimeters measured and their gonads submitted to histomorphometric analyses. The gonadal characteristics at different gestational ages were statistically compared, correlations with the fetal measurements were performed and equations to predict the gonadal characteristics from the fetal measurements were obtained. The testis weight logarithmically increased along pregnancy, whereas ovary weight increased in a linear manner. The cordonal length and number of Sertoli cells were positively correlated with the fetal measurements, being higher at 106days gestation, while the nuclear volume of these cells were negatively correlated. The total number of follicles was higher at day 80 and 106 of pregnancy. The number of oogonia decreased along the pregnancy, however, their nucleus size was increased. The number of follicles and volume of oogonia were positively correlated with the fetal measurements, while the number of oogonia was negatively correlated. Equations were obtained for the prediction of gonadal characteristics of fetuses. We concluded that in pigs testis cell proliferation, ovary development and histological organization was more pronounced during the final third of pregnancy. Fetal weight and size were strongly related to gonadal development, and can be used to estimate the histological characteristics of gonads.

High-dose testosterone and dehydroepiandrosterone induce cardiotoxicity in rats

The aim of this study is to assess cardiotoxic effect of testosterone (TES) and dehydroepiandrosterone (DHEA) in Sprague Dawley rats. We compared the impact of subacute (14 days) and subchronic (90 days) administration of suprapharmacologic doses of TES and DHEA on body weight, locomotor activity, muscle strength, echocardiographic parameters, heart histopathology, and oxidative stress markers with the control group. Testosterone (10, 30, and 100 mg/100 g body weight) and DHEA (10 mg/100 g body weight) administration decreased the body weights and locomotor activity ( p < 0.05), and the combination of both increased muscle strength ( p < 0.05) in rats. In our histopathological evaluation, misshapen cell nuclei, disorganized myocardial fibers, and leukocytic infiltrates were observed in high-dose TES (100 mg/100 g)-treated rats, especially on day 14. On day 90, mild changes such as misshapen cell nuclei, disorganized myocardial fibers, and leukocytic infiltrates were observed in TES and DHEA-treated groups. According to our echocardiographic study on day 14 and day 90, TES, especially at high doses, induced increase in left ventricular posterior wall diameter and ejection fraction ( p < 0.05). In this study, blood oxidative stress marker malondialdehyde was increased slightly but not significantly in TES and DHEA groups. On the other hand, antioxidant enzymes such as SOD and glutathione peroxidase (GSH-Px) levels were slightly but not significantly increased in TES and DHEA groups. These data demonstrate that the potential risk to cardiac health due to exogenous androgen use may be related to oxidative stress in rats.

Dose-dependent effects of Asparagus adscendens root (AARR) extract on the anabolic, reproductive, and sexual behavioral activity in rats

CONTEXT

Asparagus adscendens Roxb (Liliaceae) has a promising role in modulation of various disorders such as leucorrhea, diarrhea, dysentery, diabetes, senile pruritus, asthma, fatigue antifilarial, antifungal, spermatorrhea, and sexual debility/seminal weakness.

OBJECTIVE

To investigate dose-dependent effects of Asparagus adscendens root (AARR) extract on anabolic, reproductive, and sexual behavioral activities with a view to emphasize the pharmacological basis.

MATERIALS AND METHODS

Rats were divided into five groups: Group I (control), Groups II-IV (AARR treated, 100, 200, and 300 mg/kg body weight, respectively, orally for 30 d) and Group V (standard control treated with sildenafil citrate, 5 mg/kg body weight). On day 31, copulatory and potency tests were carried out and an autopsy was done to study the reproductive function, namely, organ weights, spermatogenesis, daily sperm production rate (DSP), and epididymal sperm counts (ESC).

RESULTS

AARR extract (200 and 300 mg/kg doses) caused a significant increase in body (p < 0.02 and p < 0.001) and testes (p < 0.01 and p < 0.001, control versus treated) weights. Reproductive activity showed significant a increase in testicular tubular diameter (p < 0.005-0.001), the number of round/elongated spermatids (p < 0.02-0.001), DSP, and ESC (p < 0.05-0.001). The sexual behavioral parameters including mounting/intromission frequency (13.0 ± 0.32/11.8 ± 0.37 and 18.2 ± 2.12/14.8 ± 1.15 versus 11.2 ± 0.66/8.2 ± 1.16), ejaculation latency (187.4 ± 1.91 and 191.4 ± 1.72 versus 180.0 ± 3.47), and penile erections (13.5 ± 0.3 and 14.5 ± 0.5 versus 8.5 ± 0.2) showed a significant increase at 200 and 300 mg/kg doses (ED50 300 mg/kg), but less than a standard control. In contrast, 100 mg/kg dose caused an increase (p < 0.005) in mounting latency only.

CONCLUSION

These results indicate increased anabolic, reproductive, and sexual activities by AARR treatment. Thus, the data provide scientific rationale for its traditional use as an aphrodisiac or for sexual disorders.

Effect of Phaleria macrocarpa on Sperm Characteristics in Adult Rats

PURPOSE

The purpose of this study was to determine the effects of Phaleria macrocarpa (PM) on male fertility by assessing its effect on the sperm characteristics which included the sperm count, motility, viability and morphology.

METHODS

Eighteen male rats were equally divided into three groups. Each group of rats was orally supplemented for 7 weeks either with PM aqueous extract (240 mg/kg), distilled water (0 mg/kg) or testosterone hormone, Andriol® Testocaps™ (4 mg/kg) respectively. On the last day of supplementation period, the rats were sacrificed and sperm was obtained from cauda epididymis via orchidectomy. The sperm count, motility, viability and morphology were determined.

RESULTS

PM aqueous extract significantly increased (p<0.05) the percentage of sperm viability. However, there was no significant effect of PM on the percentage of both sperm motility and morphology. The mean of body weight declined significantly in rats supplemented with PM aqueous extract compared to control groups (p<0.05).

CONCLUSION

The results showed that PM significantly increased sperm viability without changing the sperm motility and morphology. Hence, this study suggests that PM offers an alternative way to improve male fertility by improving the sperm quality.

Sex differences in the physiology of eating

Hypothalamic-pituitary-gonadal (HPG) axis function fundamentally affects the physiology of eating. We review sex differences in the physiological and pathophysiological controls of amounts eaten in rats, mice, monkeys, and humans. These controls result from interactions among genetic effects, organizational effects of reproductive hormones (i.e., permanent early developmental effects), and activational effects of these hormones (i.e., effects dependent on hormone levels). Male-female sex differences in the physiology of eating involve both organizational and activational effects of androgens and estrogens. An activational effect of estrogens decreases eating 1) during the periovulatory period of the ovarian cycle in rats, mice, monkeys, and women and 2) tonically between puberty and reproductive senescence or ovariectomy in rats and monkeys, sometimes in mice, and possibly in women. Estrogens acting on estrogen receptor-α (ERα) in the caudal medial nucleus of the solitary tract appear to mediate these effects in rats. Androgens, prolactin, and other reproductive hormones also affect eating in rats. Sex differences in eating are mediated by alterations in orosensory capacity and hedonics, gastric mechanoreception, ghrelin, CCK, glucagon-like peptide-1 (GLP-1), glucagon, insulin, amylin, apolipoprotein A-IV, fatty-acid oxidation, and leptin. The control of eating by central neurochemical signaling via serotonin, MSH, neuropeptide Y, Agouti-related peptide (AgRP), melanin-concentrating hormone, and dopamine is modulated by HPG function. Finally, sex differences in the physiology of eating may contribute to human obesity, anorexia nervosa, and binge eating. The variety and physiological importance of what has been learned so far warrant intensifying basic, translational, and clinical research on sex differences in eating.

Sex hormones differentially influence voluntary running activity, food intake and body weight in aging female and male rats

The aim of this study was to examine the longer-term effects of reduced gonadal hormones on food intake, food efficiency, voluntary running activity and body weight in mature male and female rats, compared to age-matched controls. We hypothesized that hormonal effects would differ for rats that were not rapidly growing and our results are consistent with this hypothesis. 6-8 month male and female rats were divided into four groups: Female and male control groups and a female and male experimental group. Control groups were intact for 46 weeks. Experimental groups were intact during Phase I (16 weeks), ovariectomized or orchidectomized during Phase II (20 weeks), and received estrogen or testosterone hormone replacement therapy (HRT) during the final Phase III (10 weeks). Food intake and running distance were monitored daily and body weight was recorded weekly for 46 weeks. Contrary to findings for young and growing animals, we did not observe a (1) stabilization of food intake in female rats following OVX, (2) loss of body weight with ORX in males, or (3) complete restoration of running activity in ORX males given testosterone, compared to females given estrogen. Feeding efficiency was not affected by aging in females or males. Loss of estrogen increased energy intake whereas reduced testosterone in males resulted in a negative energy balance. Findings suggest variable hormonal effects for aging male/female rats.

Effects of castration and subdermal silastic implants containing oestradiol-17 β-dipropionate on feedlot performance and carcass characteristics of male cattle

Feedlot performance and carcass characteristics were examined in bulls and steers with and without a subdermal Silastic capsule containing oestradiol-17β-dipropionate. Castration and/or oestrogen treatment was imposed at approximately 8 months of age. The implants were removed 56 days before slaughter, i.e. 140 days after the trial commenced. Bulls gained more rapidly (12·9%), converted food to live-weight gain more efficiently (18·0%) and yielded leaner carcasses than did steers (P < 0·05). The oestrogenic implant elevated serum oestradiol concentrations substantially (> ninefold) over that of bulls and steers and induced a castration-response in the former. Serum luteinizing hormone, testosterone and testicular growth were suppressed (P < 0·05) during the first 140 days of the trial in bulls, but returned to normal following implant removal. This response was paralleled by a reduction in average daily gain (P < 0·05) and food: gain ratio (P < 0·10). Contrary to expectations, average daily gain and food: gain ratio were not significantly improved in implanted steers. Oestrogen treatment reduced hot carcass weight, loin eye area and quality grade in both bulls and steers; the last as a result of decreased marbling and internal fat deposition. Results of this study suggest that excessive oestrogen as provided in this study via the implant fails to improve feedlot performance and carcass merit in steers and may, in fact, diminish the inherent anabolic attributes of the intact male. Additional studies are required to understand the complex interactions of androgens and oestrogens in the regulation of body growth and composition of male cattle.

A comparative study on aphrodisiac activity of some ayurvedic herbs in male albino rats

The roots of Asparagus racemosus, Chlorophytum borivilianum, and rhizomes of Curculigo orchioides are popular for their aphrodisiac and immunostimulatory properties. The herbs have been traditionally used as Vajikaran Rasayana herbs because of their putative positive influence on sexual performance in humans. Lyophilized aqueous extracts obtained from the roots of A. racemosus, C. borivilianum, and rhizomes of C. orchioides were studied for sexual behavior effects in male albino rats and compared with untreated control group animals (total N = 60). The rats were evaluated for effect of treatments on anabolic effect. Seven measures of sexual behavior were evaluated. Administration of 200 mg/kg body weight of the aqueous extracts had pronounced anabolic effect in treated animals as evidenced by weight gains in the body and reproductive organs. There was a significant variation in the sexual behavior of animals as reflected by reduction of mount latency, ejaculation latency, post ejaculatory latency, intromission latency, and an increase of mount frequency. Penile erection (indicated by Penile Erection Index) was also considerably enhanced. Reduced hesitation time (an indicator of attraction towards female in treated rats) also indicated an improvement in sexual behavior of extract treated animals. The observed effects appear to be attributable to the testosterone-like effects of the extracts. Nitric oxide based intervention may also be involved as observable from the improved penile erection. The present results, therefore, support the folklore claim for the usefulness of these herbs and provide a scientific basis for their purported traditional usage.

The influence of sex steroids on the sexual size dimorphism in the red-spotted garter snake, Thamnophis sirtalis concinnus

The red-spotted garter snake exhibits adult size dimorphism in which females are the larger sex. To understand which hormones may influence differential growth in this species, growth curves and hormone profiles of estradiol-17beta (E2) and testosterone (T) were constructed in male and female neonates. Growth was manipulated via implantation of exogenous hormones and hormone antagonists. Female neonates are heavier or longer beginning at either 20 or 24 weeks of age, respectively. Although low circulating levels of E2 and T were present in males and females from birth through 15 weeks of age, these levels were not significantly different between the sexes. Differences in the growth curves of the treated and untreated snakes were significant after 24 weeks of age. Antiestrogen produced male-like growth in females but had no effect on males. Antiandrogen had no effect on either males or females. Exogenous T reduced female growth to that observed in males, and E2 reduced male growth. These results suggest that a basal level of either E2 or T is sufficient in males to retain typical male growth patterns. Similar endogenous levels of E2 appear to have growth-promoting effects in females. Endogenous T does not appear to play a role in female growth.

Leptin, reproduction and sex steroids

Leptin is a hormone secreted mainly by the adipose cells with a primary role in the regulation of body weight by establishing a feedback loop between the energy reserves and the hypothalamic centers that control food intake. Recent data suggest that, in addition, leptin interacts with other endocrine systems to provide critical information about the size of the fat stores, acting as a permissive factor that allows the triggering of energy-demanding situations, as the onset of puberty and the reproduction, only when the size of the fuel reserve is large enough to guarantee its success. In addition, leptin appears to play a role during pregnancy and lactation, as it is produced by the placenta and is present in maternal milk. The fact that leptin levels are always higher in females, even after correcting for body fat content, suggests that the interaction between the adipose tissue and the reproductive system is modulated in a different way in males and females by androgenic and estrogenic hormones. In fact, adipose tissue samples taken from male donors are completely refractory in vitro to the action of both estrogens and androgens. On the contrary, dihydrotestosterone, androstenedione and dehydroepiandrosterone-S are potent inhibitors of leptin secretion, while estradiol induces a strong stimulation in adipose tissue taken from women. Testosterone is devoid of activity in either gender.

Gonadal steroids and energy homeostasis in the leptin era

Gonadal steroids influence food intake and body weight. Although the specific mechanisms underlying these effects are not clear, a consideration of their effects in the context of current models of energy homeostasis may ultimately lead to the identification of these mechanisms. When compared with leptin, the prototypical humoral signal of energy balance, sex steroids share many common properties related to food intake and body weight. Specifically, gonadal steroids circulate in proportion to fat mass and current energy balance, and administration of these compounds influences food intake, energy expenditure, body weight, and body composition. Moreover, both estrogens and androgens modulate central nervous system effectors of energy homeostasis that are targets for the action of leptin, including pathways that contain neuropeptide Y, pro-opiomelanocortin, or melanin-concentrating hormone. Sex steroids and leptin also regulate one another's production. Although gonadal steroids, unlike leptin, are clearly not critical to the maintenance of normal energy homeostasis, they do appear to function as physiologic modulators of this process. Identifying the specific central mediators of their effects will contribute to our understanding of their role in energy homeostasis.

Interactions among chronic cold, corticosterone and puberty on energy intake and deposition

We have shown that chronic cold stress strongly interacts with corticosterone (B) to determine subsequent regulation of the hypothalamo-pituitary-adrenal (HPA) axis responses to novel stress. These studies, using the same 2 sets of rats, show that chronic cold also interacts with B and testosterone on signals of energy balance. The two groups of rats differed in weight by 20% and in age by 2 weeks (44-59 days of age). Adrenalectomized rats, replaced with varying doses of B, were exposed to cold or served as controls. Food intake and body weight during the experiments and hormones, metabolites and fat depots were measured on day 5. B, but not cold, affected food intake in the younger rats; by contrast, cold, but not B, affected food intake in the older rats. Testosterone was higher in older control rats and was markedly depressed by cold; younger rats had lower testosterone that was minimally affected by cold. Weight gain decreased in all rats at room temperature with increasing B, whereas they all lost weight in cold independently of B. Cold stimulated and B inhibited interscapular brown adipose tissue DNA content (reflecting sympathetic stimulation of thermogenesis). B stimulated insulin, whereas cold inhibited leptin and insulin; B also increased white adipose tissue weight gain in controls and inhibited its loss in cold. Leptin was unrelated to white adipose tissue depots in older control rats but was strongly related to these stores in younger rats and in all rats in cold. We conclude that: 1. By decreasing signals that act centrally to inhibit food intake (insulin, leptin and testosterone) cold allows B to stimulate food intake; 2. B inhibits weight gain although it causes accrual of fat; 3. Cold, probably through sympathetic stimulation of white adipose tissue, causes fat loss which is modulated by the inhibitory effect of B on sympathetic outflow; and, 4. The slope of the relationship between fat depot size and leptin becomes flatter in cold, possibly because of increased sympathetic outflow to these depots.

Transdermal testosterone administration in women with acquired immunodeficiency syndrome wasting: a pilot study

Although human immunodeficiency virus (HIV) disease is increasing rapidly among women, no prior studies have investigated gender-based therapeutic strategies for the treatment of acquired immunodeficiency syndrome (AIDS) and its complications in this population. Markedly decreased serum androgen levels have been demonstrated in women with AIDS and may be a contributing factor to the wasting syndrome in this population. To assess the effects of androgen replacement therapy in women with AIDS wasting, we conducted a randomized, placebo-controlled, pilot study of transdermal testosterone administration. The primary aim of the study was to determine efficacy in terms of the change in serum testosterone levels, safety parameters and tolerability. A secondary aim of the study was to investigate testosterone effects on weight, body composition, quality of life, and functional indexes. Fifty-three ambulatory women with the AIDS wasting syndrome defined as weight less than 90% of ideal body weight or weight loss of more than 10% of the preillness maximum, free of new opportunistic infection within 6 weeks of study initiation, and with screening serum levels of free testosterone less than the mean of the normal reference range (< 3 pg/mL) were enrolled in the study. Subjects were age 37 +/- 1 yr old (mean +/- SEM), weighed 92 +/- 2% of ideal body weight, and had lost 17 +/- 1% of their maximum weight. CD4 count was 324 +/- 36 cells/mm3, and viral burden was 102,382 +/- 28,580 copies. Subjects were randomized into three treatment groups, in which two placebo patches (PP), one active/one placebo patch (AP group), or two active patches (AA group) were applied twice weekly to the abdomen for 12 weeks. The expected nominal delivery rates of testosterone were 150 and 300 microg/day, respectively, for the AP and AA groups. Forty-five subjects completed the study (PP group, n = 13; AP group, n = 14; AA group, n = 18). Two additional subjects from the PP group and two from the AP group were included in the intent to treat analysis. Serum free testosterone levels increased significantly from 1.2 +/- 0.2 to 5.9 +/- 0.8 pg/mL (AP) and from 1.9 +/- 0.4 to 12.4 +/- 1.6 pg/mL (AA) in response to testosterone administration (P < 0.0001 for comparison of AA vs. PP and AP vs. PP; normal range, 1.3-6.8 pg/mL). Testosterone administration was generally well tolerated locally and systemically, with no adverse trends in hirsutism scores, lipid profiles, or liver function tests. Weight increased significantly in the AP group (1.9 +/- 0.7 kg) vs. the PP group (0.6 +/- 0.8 kg; P = 0.043), but did not increase significantly in the AA group (0.9 +/- 0.4 kg; P = 0.263 vs. PP, by mixed effects model assessing the interaction of time and treatment on all available data, one-tailed test). Improved social functioning (P = 0.024, by one-tailed test) and a trend toward improved pain score (P = 0.059) were observed in the AP vs. the PP-treated patients (RAND 36-Item Health Survey questionnaire). Five of six previously amenorrheic patients in the AP group had spontaneous resumption of menses compared to only one of four amenorrheic patients in the AA group (P = 0.045 for comparison of actual number of periods during the study). This study is the first investigation of testosterone administration in women with AIDS wasting. We demonstrate a novel method to augment testosterone levels in such patients that is safe and well tolerated during short term administration. At the lower of the two doses administered in this study, testosterone therapy was associated with positive trends in weight gain and quality of life. Higher, more supraphysiological, dosing was not associated with positive trends in weight or overall well-being. These data suggest that testosterone administration may improve the status of women with AIDS wasting. Further studies are needed to assess the effects of testosterone on weight in HIV-infected women and to define the optimal therapeutic window for test

Aromatase inhibition impairs skeletal modeling and decreases bone mineral density in growing male rats

Aromatization of androgens into estrogens may explain some of the skeletal action of androgens. We examined the effect of the aromatase inhibitor Vorozole (VOR) on skeletal growth and mineral accumulation in growing 6-week-old male Wistar rats. Rats were either Sham-operated (Sham) or Orchidectomized (Orch) and treated with or without the aromatase inhibitor VOR. One Sham-operated group was killed at Baseline (Base); the four other groups (Sham, Sham + VOR, Orch, Orch + VOR) were killed 18 weeks after surgery. As expected, all groups gained body weight, but body weight gain was significantly (-25%) lower in Orch, Orch + VOR, and Sham + VOR. Both bone formation, as assessed by serum osteocalcin, and bone resorption, as assessed by urinary (deoxy)pyridinoline, decreased significantly in all groups compared with Base. Orchidectomy resulted in a relative increase of biochemical markers of bone formation and resorption compared with Sham. Treatment with VOR, however, resulted only in a very moderate increase of (deoxy)pyridinoline compared with Sham. As expected, femoral length increased compared with Base, but orchidectomy reduced the relative growth of the femur whereas VOR did not influence femoral length. Ex vivo, densitometric and geometric properties of the femora were evaluated by peripheral computerized quantitative tomography (pQCT) and dual-energy x-ray absorptiometry (DXA). The lumbar vertebrae were measured by DXA. At the end of the experimental period, volumetric trabecular bone mineral density (vTBMD) measured at the distal end of the femur was significantly lower not only in both Orch groups but also in Sham + VOR. The decrease of cancellous bone density in Sham + VOR was lower than in the orchidectomized animals. A relative decrease of femoral inner and outer diameters compared with Sham and Base was observed in both Orch groups and in Sham + VOR, suggesting that both orchidectomy and VOR-treatment inhibited periosteal bone formation and endosteal bone resorption. Only orchidectomy, however, resulted in a decrease of cortical thickness. Bone area, mineral content, and density of both femora and lumbar vertebrae, measured by DXA, were decreased to a similar extent by VOR and Orch (bone mineral content of the femur was 467 +/- 18 mg in Orch and 461 +/- 10 mg in Sham +/- VOR vs. 521 +/- 11 mg in Sham; P < 0.001). In conclusion, treatment with the aromatase inhibitor VOR impairs body weight gain and skeletal modeling and decreases bone mineral density. Aromatase inhibition had similar final effects on bone mass and size as castration, but with less marked effects on bone turnover.

Evidence for sex steroid inhibition of lipoprotein lipase in men: comparison of abdominal and femoral adipose tissue

Plasma estradiol has been suggested to suppress adipose tissue lipoprotein lipase (LPL) activity in women. The present study explores the regulation of LPL by sex steroids in sedentary obese men (N = 24) at their usual weight. Femoral adipose tissue LPL activity, eluted with serum and heparin or extracted with detergent, showed significant inverse correlations with plasma levels of testosterone, bioavailable testosterone, dihydrotestosterone, and estradiol. Both measures of femoral LPL activity were also correlated with the weight change occurring despite efforts to maintain a constant weight. Abdominal LPL activity showed significant but weaker inverse correlations with bioavailable testosterone only. Multivariate analysis of potential predictors for eluted femoral LPL activity showed that plasma testosterone, dihydrotestosterone, and estradiol were interdependent, whereas the rate of weight change was an independent variable. In the regression equation, only bioavailable testosterone and weight change were retained, explaining 63% of the variability (R = .79, P = .0002). These results suggest that sex steroids suppress adipose tissue LPL activity in men, and more so in the thigh than in the abdomen, thereby possibly contributing to a central fat accumulation. The data are compatible with a model from male animals suggesting that testosterone effects on adipose tissue LPL are mediated by estradiol formed locally.

Short day-induced depletion of lipid stores is fat pad- and gender-specific in Siberian hamsters

The naturally occurring, short day (SD)-induced decrease in body mass in male Siberian hamsters is due almost exclusively to decreases in body fat during the first few weeks of SD exposure. This decrease in body fat is not uniformly distributed among the white adipose tissue (WAT) pads. The purpose of the present experiment was to answer four questions: (i) Are the SD-induced preferential decreases in internally located fat pad mass gender specific?; (ii) Does gonadectomy and/or steroid replacement therapy alter this pattern of body fat depletion?; (iii) What is the role of lipoprotein lipase (LPL) activity in this process?; and (iv) Does SD-induced functional castration affect food intake, body mass and lipid-related fat responses similarly to surgical castration? Adult male and female Siberian hamsters were housed in long days (LD) for 6 wk following castration (CAST) or ovariectomy (OVX) combined with either SC implants of testosterone (T), estradiol or the cholesterol control (CHOL). While the remaining animals of both sexes remained gonadally intact. At this time, half the animals in each group were transferred to SDs for 6 wk. SD-housed gonad-intact males and females exhibited gonadal regression and decreased body mass and carcass lipid; however the pattern of lipid depletion from the WAT pads was gender specific. SD-exposed gonad-intact males showed disproportionate decreases in fat pad mass in the internally located epididymal WAT (EWAT) and retroperitoneal WAT (RWAT) fat pads compared with the more externally located intraperitoneal WAT (IWAT) pad, whereas females showed uniform relative decreases for all pads and regardless of their reproductive status. CAST + CHOL or T eliminated the SD-induced fat pad-specific pattern of lipid depletion in males. Therefore, the slowly decreasing serum T concentrations triggered by the initial exposure to SDs may underlie the fat pad-specific differential depletion of lipid. The photoperiod-, gonadectomy-, and hormone replacement therapy-induced changes in fat pad mass were seldom associated with parallel changes in specific LPL activity. CAST and SD exposure both reduce serum T concentrations, decrease body mass via reductions in the same carcass components and decrease food intake; however, these the two treatments differ with respect to their effects on WAT mass and LPL activity. Specifically, SD exposure decreases IWAT, EWAT and RWAT mass, whereas CAST decreases only EWAT mass. In addition, specific LPL activity is not affected by SD exposure, whereas CAST generally increases specific LPL activity in all pads compared to their gonad-intact controls.

A role for testosterone in the maintenance of seasonally appropriate body mass but not in lipectomy-induced body fat compensation in Siberian hamsters

The purpose of this study was to test whether serum testosterone (T) concentrations characteristic of reproductively active, long-day-housed Siberian hamsters are necessary for compensatory increases in nonexcised fat pads following removal of epididymal white adipose tissue (EWAT) and/or for the maintenance of seasonally appropriate body weights in these hamsters. Long-day-housed hamsters were castrated or left intact, sham or EWAT lipectomized, and given T or cholesterol (C) implants. All groups had ad libitum food access except for two castrated T-treated groups that were pair-fed to their C-treated counterparts to control for effects of T on food intake. C-treated castrates had decreased body weights compared with all other groups, suggesting a role of T in the maintenance of seasonally appropriate body mass. Since the T-treated hamsters pair-fed to these T-deficient animals exhibited seasonally appropriate body weights and fat pad masses, T does not appear to affect these parameters through the modulation of food intake. All fat pads of C-treated animals were smaller than those of ad libitum- or pair-fed, T-treated castrates; however, EWAT was the only fat pad that was smaller in the C-treated sham-lipectomized group than in gonad-intact sham-lipectomized hamsters. This result may indicate an enhanced sensitivity of EWAT to T. The effects of T on fat pad mass were not associated with proportionate changes in lipoprotein lipase activity, suggesting that the major effect of T on fat accumulation occurs through other mechanisms in this species. C-treated lipectomized hamsters compensated for the body fat deficit 8 weeks after lipectomy via statistically non-significant increases in retroperitoneal and inguinal WAT mass. This finding suggests that, whereas T is necessary for maintenance of seasonally-appropriate body weight, it is not necessary for fat pad compensation after EWAT lipectomy.

Threshold photoperiods for the induction of short day traits in collared lemmings (Dicrostonyx groenlandicus)

When exposed to short photoperiod collared lemmings undergo a number of physiological and morphological changes including an increase in body weight, a change in body composition, development and enlargement of the bifid "digging" claw, and a molt to a white winter pelage. We investigated the threshold photoperiods for the induction of these traits in male and female lemmings born and raised under a 22L:2D photoperiod and transferred at weaning (19 days of age) to various other photoperiods. Male lemmings showed the characteristic increase in body weight when exposed to 16 hr of light or less per day whereas females required a photoperiod of 14 hr of light or less per day to elicit an increase in body weight. The threshold photoperiods for the increase in bifid claw size were 16 and 18 hr of light per day in male and female lemmings, respectively. The molt to the white winter pelage began under a longer photoperiod in females (16L:8D) than in males (14L:10D). Testes and seminal vesicles were significantly inhibited by photoperiods of 22L:2D and 20L:4D. Likewise, uterine weights were inhibited by maintenance on a photoperiod of 22L:2D. Taken together, these data show that the threshold photoperiods for the induction of the short day traits in collared lemmings are both trait- and sex-dependent. These observations also suggest that under some conditions, exposure to long photoperiods can inhibit sexual maturation.

Androgenic induction of brain sexual dimorphism depends on photoperiod in meadow voles

Male meadow voles maintained in a long photoperiod (LP) from birth have heavier brains than do females, but in short photoperiods (SP) this sex dimorphism is absent. Testosterone propionate (TP) administration on the second day of postnatal life produced significant increases in brain weight of LP but not SP females at 35 days of age. Short daylengths reduce the responsiveness of the meadow vole nervous system to the masculinizing effects of perinatal testosterone and may, in part, mediate the seasonally reduced sex difference in brain weight.

Lower endogenous androgens predict central adiposity in men

Central adiposity, sometimes described as male pattern fat distribution, is adversely related to cardiovascular risk and mortality independent of other measures of obesity. In a cohort of 511 men aged 30 to 79 years in 1972 to 1974, levels of androstenedione, testosterone, and sex hormone-binding globulin measured at baseline were inversely related to subsequent central adiposity, estimated 12 years later using the waist-hip circumference ratio. The observed differences in waist-hip ratio between top and bottom tertiles of these hormones and sex hormone-binding globulin were similar to mean waist-hip ratio differences between men with stroke or ischemic heart disease and those without in another prospective study. These findings, consistent with studies suggesting that testosterone seems to mobilize the abdominal depot on males, suggest that "male pattern" fat distribution may be a misleading description for central adiposity, at least, in men. Degree of maleness as indicated by total androgen levels is, in fact, negatively associated with central adiposity. However, the role of sex hormone-binding globulin in regulating androgenic activity warrants further investigation.

Androgen treatment prevents loss of cancellous bone in the orchidectomized rat

This report describes histomorphometric evidence for an important role of androgens in maintaining cancellous bone balance at a remodeling site in vivo. Rats were orchiectomized (ORX) at 7 weeks of age and received either androgens or vehicle 1 week later (testosterone, 1-dehydrotestosterone, or 5-dihydrotestosterone) by subcutaneous pellet, producing controlled release of the drug for 3 weeks. Intact male rats and untreated ORX animals served as controls. After 4 weeks untreated ORX resulted in undetectable serum testosterone levels and marked atrophy of seminal vesicles compared with intact controls. Histomorphometry revealed severe cancellous osteopenia in the secondary spongiosa of the proximal tibial metaphysis. The length of bone surface lined by apparently "active" osteoblasts and number of osteoclasts per length of cancellous bone surface were increased following ORX. Testosterone treatment at 5 mg (per 21 days) produced subphysiologic serum testosterone levels. In contrast, 10 and 25 mg pellets resulted in serum testosterone ORX, and the degree of protection was dose dependent. 1-Dehydro- and 5-dihydrotestosterones displayed a bone-protective effect similar to that of testosterone. The results demonstrate that gonadal insufficiency results in a cancellous osteopenia that is preventable by testosterone treatment. Further, because a similar protective action was achieved using the nonaromatizable androgen 5-dihydrostestosterone, the results suggest that this bone-sparing effect is mediated by androgen rather than by metabolism of the androgen to an estrogen.

Up-regulation of androgen receptor binding in male rat fat pad adipose precursor cells exposed to testosterone: study in a whole cell assay system

Binding of androgens to adipocytes has previously been evaluated using cytosol fractions without taking into account nuclear binding, although the latter is suggested to be close to the physiological site of action. In the present study, performed in differentiated fat pad adipose precursor cells, we describe a simple, reliable and reproducible androgen binding assay in a system with intact cells. Tritiated and unlabeled methyltrienolone (R1881) were used to define specific and unspecific androgen binding. Triamcinolone acetonide was added to prevent the binding of R1881 to other types of receptors. Differentiated adipose precursor cells contain a homogeneous class of high affinity androgen binding sites, and binding is saturable and reversible. Binding apparently occurs at one site, with a Kd in the range of physiological androgen concentration (about 4 nM). Competition studies indicate that the receptor is specific for R1881, testosterone and dihydrotestosterone, which have approximately the same affinity, while progesterone, estradiol and dexamethasone show much lower affinity. Androgen binding was markedly enhanced after cellular exposure to R1881 and testosterone but not dihydrotestosterone, and this increase was dependent on protein synthesis, suggesting the formation of new receptors by these androgens. In conclusion, fully differentiated adipocytes contain a specific, high affinity receptor, the density of which is dependent on androgens.

Testosterone regulates metabolism of plasma chylomicrons in rats

Previously we demonstrated a marked sex difference in the metabolism of chylomicrons in adult rats. In males, radiolabeled chylomicrons displayed a longer dwell time on endothelial surfaces, which resulted in a decreased chylomicron uptake by the liver. The increased rate of chylomicron metabolism in females was associated with increased postheparin lipoprotein lipase activity. In the present study, we have investigated the effects of physiological doses of sex steroid hormones on the metabolism of chylomicrons and postheparin lipoprotein lipase activity. No sex differences were found in prepubertal animals. We also found no difference in chylomicron metabolism in control female, castrated female, estrogen-treated female, castrated male, and estrogen-treated male rats. However, control male, testosterone-treated male, and testosterone-treated female rats showed increased endothelial binding of chylomicrons and decreased chylomicron uptake by the liver. Postheparin lipoprotein lipase activity also was decreased by testosterone administration. In parallel with the alterations in chylomicron metabolism, serum high density lipoprotein levels in male rats decreased with testosterone administration. These results indicate that the differences in chylomicron metabolism, postheparin lipoprotein lipase activities, and serum high density lipoprotein levels observed between male and female rats are due to testosterone.

Differential effects of gonadal function on bone histomorphometry in male and female rats

The effects of castration on bone histomorphometry and mineral homeostasis were compared in male and female rats. Measurements were performed 4 weeks after sham operation or gonadectomy. Orchiectomy produced increases in serum calcium and decreases in serum testosterone and androstenedione, whereas ovariectomy produced decreases in serum estradiol and testosterone. Orchiectomy did not alter static bone histomorphometric measurements of the tibial diaphysis, whereas ovariectomy increased cross-sectional and medullary areas, lowered endosteal tetracycline-labeled surface length, and markedly increased endosteal nonlabeled surface length. Orchiectomy decreased mean periosteal bone formation rate and mean periosteal bone apposition rate, whereas ovariectomy increased both measurements. Orchiectomy and ovariectomy markedly diminished trabecular area and trabecular surface length at the tibial metaphysis. Orchiectomy did not alter the number of osteoclasts per mm trabecular surface or the percentage of trabecular surface covered by osteoclasts, whereas ovariectomy increased both measurements. These findings indicate that gonadal hormones produce separate and distinct effects on bone metabolism as determined by histomorphometry in male and female rats.

Seasonal weight changes in male rhesus monkeys (Macaca mulatta)

Adult male rhesus monkeys lose weight during the breeding season and regain it during the nonbreeding season. The annual pattern of maximum weight gain just prior to the onset of breeding resembles the seasonal "fattening" seen in squirrel monkeys, but the period of weight gain is less discrete. The magnitude of weight change is less in younger males, in that sexually immature males gain weight in both seasons, but significantly less during the breeding season. Females do not lose weight during the breeding season. Post hoc analyses revealed no significant correlations between male testosterone levels, dominance ranks, weights, or weight changes. The heaviest animals as juveniles were predictably the heaviest as adolescents. The timing of seasonal changes in testosterone did not correlate with the timing of changes in weight; weight losses followed the rise in testosterone, and weight gains continued until early in the breeding season after testosterone levels had already begun to rise. It is suggested that seasonal hormonal changes may influence activities in individuals and that changes in the activities of particular group members may alter the activity patterns of other group members. This alteration of activity patterns due to group influences on individuals as well as individual influences on the group may explain why hormonal regulation of seasonal weight appears to be indirect and why individuals (juveniles) experiencing no seasonal hormonal changes nonetheless show differences in activity patterns and seasonal weight changes.

Androgenic influences on body size and composition of adult rhesus monkeys

The effects of daily treatment with testosterone propionate (TP, 2 mg/kg) and dihydrotestosterone propionate (DHTP, 2 mg/kg) were examined in rhesus monkeys in three experiments. In experiments 1 and 2, males and females gonadectomized in infancy, and female pseudohermaphrodites produced by prenatal exposure to TP or DHTP and gonadectomized postpubertally, were studied in conjunction with intact males (IM). The IM group was heavier in adulthood than the three gonadectomized groups, which did not differ in body weight from each other. Genetic males had greater crown-rump length than genetic females. Treatment of the gonadectomized groups with TP produced large increases in body mass (averaging approximately 50%) that were attributable to accretion of lean tissue. This effect did not differ significantly between males and females. In experiment 3, additional groups of males that had been castrated as infants were given daily injections with DHTP or oil. The DHTP treatment resulted in increases in body size that were not different from those seen following TP treatment. When TP and DHPT treatments were discontinued, body weights and dimensions reverted to base-line values. Increased body size induced by TP and DHTP was accomplished without reliable increases in food intake. Because testosterone (T) is metabolized to dihydrotestosterone (DHT), while DHT cannot be converted to T, these results show that both T and DHT are effective anabolic hormones in rhesus.

Relationship between lipoprotein lipase activity and plasma sex steroid level in obese women

In obese women (n = 16) at their weight, fasting adipose tissue lipoprotein lipase (LPL) activity, obtained by elution with serum and heparin at 4 degrees and 37 degrees C, was inversely correlated to plasma estradiol levels (r = -0.724; P = 0.002) and (r = -0.641; P = 0.010), respectively. Furthermore, fasting postheparin plasma LPL activity during a heparin infusion, showed an even stronger inverse correlation to plasma estradiol when measured at 60 min (r = -0.815; P less than 0.001). None of the above parameters was correlated to the body mass index. Postprandial LPL activity in postheparin plasma, measured 10 min after a heparin injection, showed a strong positive correlation with plasma free testosterone (r = 0.780; P = 0.001). Neither of these parameters was correlated with the body mass index. The origin of this LPL activity is presently unknown but could conceivably represent a pool of LPL from skeletal muscle. Since it has been shown convincingly that estrogen decreases adipose tissue LPL activity in the rat, the present studies strongly suggest that estradiol is a major negative regulator of fasting adipose tissue LPL activity in women.

Distribution of androgen receptor in microdissected brain areas of the female baboon (Papio cynocephalus)

We measured androgen receptors in the brain and pituitary of 4 female baboons (Papio cynocephalus) by the in vitro binding of methyltrienolone (R1881) to cytosols from 17 brain subregions as well as anterior and posterior pituitaries. High levels of AR were detected in anterior (22.1 +/- 7.1 (S.E.M.) fmol/mg protein) and posterior pituitary (12.6 +/- 3.3 fmol/mg protein). In brain tissue, the highest androgen receptor levels were found in the infundibular nucleus/median eminence (9.4 +/- 2.3 fmol/mg protein), ventromedial nucleus (6.3 +/- 1.7 fmol/mg protein) and periventricular area (4.9 +/- 1.3 fmol/mg protein). Saturation analysis of anterior pituitary and brain tissue (pool of hypothalamic, preoptic area, amygdala and septum remaining after microdissection of brain nuclei) showed that [3H]R1881 binds to the androgen receptor with high specificity and affinity (Kd = 1.25 x 10(-10) M, 0.45 x 10(-10) M, in anterior pituitary and HPA cytosol, respectively). Serum testosterone levels were low in all animals (0.59 +/- 0.26 ng/ml). With these data we described the quantitative distribution of androgen receptor in the pituitary and in specific brain nuclei in a species of nonhuman primate. The distribution is similar in many respects to that described in the male rat and the data suggest a conservation of androgen receptor distribution across species.

Androgens exert opposite effects on body mass of heavy and light meadow voles

The influence of gonadal hormones on body mass of adult male meadow voles varied systematically as a function of the animals' baseline body weight; heavier voles decreased and lighter voles increased their body mass after castration. Testosterone replacement reversed the effects of castration; changes in body mass during hormone treatment were negatively correlated with changes observed after castration. Body mass of intact males was not correlated with plasma testosterone titers. Individual differences in body mass of male voles appear to reflect variations among animals in substrate responsiveness to hormones rather than differences in circulating hormone levels.

The involvement of gonads and gonadal steroids in the regulation of food intake, body weight and adiposity in the white Leghorn cock

The effects of long-term injections of testosterone propionate (TP), diethylstilbestrol (DES) and TP+DES simultaneously to castrated and sham-operated White Leghorn cocks on feeding, weight gain, obesity, blood lipids and weight of various glands were studied. DES induced marked adiposity while TP reduced carcass fat content. Injections of TP+DES induced only moderate obesity. The responses of the castrated cocks to TP or DES were not always parallel to those of the sham-operated ones. In sham-operated cocks, TP induced permanent hypophagia and emaciation while in castrated cocks, although alleviating adiposity, it did not reduce the rate of weight gain and induced only a transient hypophagia. DES induced permanent hyperphagia and accelerated weight gain in sham-operated cocks while in those castrated, it induced only transient hyperphagia which later on changed into hypophagia. Although the latter cocks did not gain more weight than those castrated with no steroids supplementation, they were much more obese and had a fat content similar to that of the sham-operated ones treated with DES. The castration was found to alleviate the depressing effect of TP on adenohypophyseal and thyroidal weights. The results may suggest: (1) In the White Leghorn cocks, DES increases lipogenesis and food intake while TP results in the contrary. (2) Castration should not be considered as a lack of gonadal steroids only.

Testosterone affects food intake and body weight of weanling male rats

The effects of testosterone propionate (TP) on food intake and body weight were investigated using castrated prepubertal male rats. Regardless of dose (1 mg, 0.2 mg or 0.1 mg), daily injections of TP increased body weight gain and food intake during the prepubertal period (from 22 to 40 days to age). Considering previous results, the present observations suggest that in the male rat sensitivity to the effects of gonadal hormones on feeding develops earlier than in females.

Gender and energy balance: sex differences in adaptations for feast and famine

According to this theory/review, the cross-culturally common finding of more women than men among the obese is at least in part a consequence of sex differences in evolutionary selection pressure. James and Trayhurn claim that the propensity to obesity is linked to th ability to survive a fast and both may involve reduced heat production. The present theory extends this relationship to sex differences in energy balance. According to the theory proposed here, mammalian females were subjected to more severe selection pressures during times of short food supply than males were and hence females were under more pressure to evolve mechanisms to facilitate survival during famine, which led to sex differences in obesity. The data relevant to sex differences in starvation survival, obesity and heat production, and the possible evolutionary roles and implications of sex differences in chromosomes and in organizational and activational sex hormones are reviewed. The conclusion is that evolution has created a linkage between sex chromosomes, hormones and energy balance, and this linkage is at least in part responsible for the greater resistance of the female to famine and for her greater tendency to become obese in times of feast.