Sex differences in adrenal function in the lizard Cnemidophorus sexlineatus: I. Seasonal variation in the field.

In order to document sex differences in adrenal function and how this relates to gonadal function during the period of seasonal activity, blood samples from male and female six-lined racerunners, Cnemidophorus sexlineatus, were taken immediately after capture in the field for determination of plasma corticosterone and gonadal steroid concentrations. Plasma testosterone and dihydrotestosterone levels for males, and 17 beta-estradiol and progesterone levels for females, were measured. Trends in the concentration of plasma corticosterone differed significantly between males and females. In males the highest concentrations of corticosterone were measured in late spring and the lowest concentrations were measured in late summer. Whereas half of the variation in corticosterone levels among males could be explained as seasonal change, less than 1% of the variation among females could be explained as seasonal change. In males plasma corticosterone and androgens exhibited similar seasonal decreases. Corticosterone levels for females were not correlated with progesterone or 17 beta-estradiol levels. Sex differences in seasonal variation in plasma corticosterone concentrations suggest that corticosterone may be involved in the different reproductive strategies and energy requirements of males and females during the seasonal period of activity.     

Plasma corticosterone concentrations in males of the skink Egernia whitii during acute and chronic confinement, and over a diel period

This study examined adrenal and gonadal responses to capture and to longer term captivity in males of the scincid lizard, Egernia whitii. Animals subjected to acute capture stress in the field exhibited a rapid rise in plasma corticosterone concentrations that had not attenuated by 4 h after capture; plasma testosterone concentrations decreased significantly over this period. Animals returned to captive conditions in the laboratory showed little change in plasma corticosterone concentrations by 1 week, but concentrations were significantly lower at 4 weeks. Plasma testosterone did not vary significantly during this period. Sampling over a diel period indicated that plasma corticosterone concentrations vary little over the daylight hours; however, there was a significant decrease between the samples taken at 17:00 h and 21:00 h. These results suggest that, as in other species, the acute adrenal response to capture stress may confound assessment of other physiological parameters, although if experiments are carried out during daylight hours, time of sampling should have little influence on plasma corticosterone concentrations. The results also suggest that males of E. whitii require at least a week to adapt to captivity, although further studies investigating different captive conditions are warranted for this social species.     

The breeding season duration hypothesis: acute handling stress and total plasma concentrations of corticosterone and androgens in male and female striped plateau lizards (Sceloporus virgatus)

Acute glucocorticoid elevations can be adaptations to short-term stressors. The breeding season hypothesis predicts reduced glucocorticoid responsiveness to acute stressors in populations or species with short breeding seasons. The striped plateau lizard (Sceloporus virgatus) has a short breeding season in Arizona. We measured plasma corticosterone and total androgen levels (dihydrotestosterone and testosterone) following one of the four stress-handling treatments (0, 10, 60, or 180 min). In both sexes, longer handling stress yielded higher corticosterone; females had higher corticosterone than males at all time points. Androgens did not vary with handling duration, in either sex. Combining treatments, plasma androgens correlated positively with corticosterone (CORT) in females but not in males; plasma CORT and body mass residuals were negatively correlated in both sexes, suggesting lizards in poor body condition and/or not investing heavily in reproduction (follicle mass) have higher acute corticosterone. Total plasma androgens and body mass residuals were positively associated in males, but showed no association in females. The maximal CORT elevation after handling stress in this single-clutching species was of comparable magnitude to responses in related multi-clutching lizard species with longer breeding seasons. Using data from studies of multiple populations of three Sceloporus species, we found no relationship between the relative magnitude of the CORT increase and either latitude or elevation, two variables in the literature correlated with duration of the breeding season, and only weak relationships with geographic elevation and actual (not relative) stress-elevated CORT values in this multi-population comparison.     

Members of opposite sex mutually regulate gonadal recrudescence in the lizard Calotes versicolor Agamidae)

Adult males and females of the seasonally breeding lizardCalotes versicolor were subjected to various social situations under semi-natural conditions to explain the role of socio-sexual factors in gonadal recrudescence. They were grouped as: (i) males and females, (ii) males and females separated by a wire mesh, (iii) same sex groups of males or females, (iv) castrated males with intact females and (v) ovariectomized (OvX) females with intact males from postbreeding to breeding phase. Specimens collected from the wild during breeding season served as the control group. Plasma sex steroid levels (testosterone in male and 17β-estradiol in female), spermatogenetic activity and vitellogenesis were the criteria to judge gonadal recrudescence. In intact males and females that were kept together, gonadal recrudescence and plasma sex steroids levels were comparable to those in wild-caught individuals. Gonadal recrudescence was at its least in all male and all female groups, and plasma sex steroids were at basal levels. Association with OvX females initiated testicular recrudescence but spermatogenetic activity progressed only up to the spermatid stage while males separated from females by wire mesh showed spermatogenetic activity for a shorter period. Females grouped with castrated males and those separated from males by wire mesh produced vitellogenic follicles. However, the total number and diameter of vitellogenic follicles, and plasma estradiol levels were lower than in the females grouped with intact males. The findings indicate that association with members of the opposite sex with progressively rising titers of sex steroids is crucial in both initiating and sustaining gonadal recrudescence in the lizard. Thus, members of the opposite sex mutually regulate gonadal recrudescence in theC. versicolor.     

The effect of maternal and fetal corticosteroids on the development of function of the pituitary-adrenocortical system.

The pituitary-adrenocortical system of rat fetuses was stimulated (larger adrenals at birth) by maternal adrenalectomy, or suppressed (smaller adrenals at birth) by implantation of an ACTH secreting pituitary tumor (MtTF4). Offspring were delivered by caesarean section and fostered to untreated females. Offspring of intact females delivered by caesarean section and normally delivered offspring of intact mothers both fostered to untreated lactating females served as controls. Body growth in the first three weeks of life was delayed in offspring of tumor bearing mothers in Control-fostered subjects as compared to the 2 other groups. At 70 days of age female offspring of the tumor implanted and adrenalectomized mothers, as well as the Control-caesarean females, had smaller adrenals than Control-fostered animals of the same sex. The adrenal size of males was not significantly affected. No significant differences were found in resting concentrations of corticosterone in plasma, although offspring of adrenalectomized mothers had high values. Suppressed adrenal response to ether stress was found in offspring of tumor bearing mothers. The supposition is that interference with maternal pituitary-adrenocortical activity during pregnancy has a long lasting effect on fetal hypothalamo-pituitary-adrenocortical system.     

Adrenal function in female rats before puberty: the effects of gonadectomy

The following study was designed to test whether the change in the amplitude of the adrenal rhythm and the response to stress seen at puberty in female rats is dependent upon stimulation of the adrenal system by gonadal steroids. Rats were gonadectomized either at two days of age or at 21 days of age and periodic blood samples were taken by cardiac puncture and assayed for corticosterone (B) by a fluorometric procedure. Ovariectomy at weaning age (21 days) had no effect on adrenal function until the time of normal puberty onset. In intact animals, a rise in resting levels of corticosterone and an increase in the incremental response to ether stress was noted at 35 days of age. (Puberty in females was 35.3 ± 1.2 days as indicated by vaginal opening). Ovulation occurred the following day in 9/10 rats. Gonadectomy at two days of age had essentially the same effect as later gonadectomy in females. By 70 days of age, resting corticosterone values and stress responses in gonadectomized females reached levels similar to intact females. It is concluded that an independent adrenarche can occur in females but that gonadal steroids present at the time of puberty modulate the timing of this process.     

Sexually dimorphic effects of morphine and MK-801: sex steroid-dependent and -independent mechanisms.

Rats show gender differences in responses to morphine and the N-methyl-D-aspartate receptor antagonist dizocilpine (MK-801); the role of sex steroids in mediating these differences is unclear. We tested the overall hypothesis that circulating gonadal steroids determine the gender differences in morphine- and MK-801-induced behavior and c-Fos expression. Morphine caused a greater expression of c-Fos in the striatum of intact males than of that females, which was independent of sex steroids. MK-801 completely inhibited morphine-induced c-Fos in intact females but only caused partial inhibition in intact males; castrated males showed complete inhibition, which was reversed by testosterone, but gonadal steroids had no effect on this response in females. In thalamus, there was a large sex difference in the response to MK-801 that was independent of gonadal steroids. Behavioral responses to morphine were greater in males, but responses to MK-801 were greater in females; both were sex steroid independent. These findings show significant sex differences in response to morphine and MK-801 that are mediated by sex steroid-dependent and -independent mechanisms, which may be important in treatment outcomes of drug addiction.     

Corticosterone responses of grey-faced petrels (Pterodroma macroptera gouldi) are higher during incubation than during other breeding stages

We report the results of the first field study examining seasonal changes in corticosterone responses of typically long-lived birds of the order Procellariiformes. In particular, we examined whether grey-faced petrels Pterodroma macroptera gouldi showed changes in circulating baseline corticosterone concentrations and corticosterone responses to a standardized handling protocol across the breeding season. Such changes have been associated with changes in body condition and variations in energy demands on adult birds through the breeding season. During early incubation, males were in significantly better condition than females that had just completed laying, whereas during late incubation, males were in significantly poorer condition than females. In spite of these differences, there was no significant difference in baseline corticosterone concentrations between sexes or among birds at different reproductive stages. However, we detected significant differences in corticosterone responses associated with a standardized handling protocol at different stages through the breeding season. Responses were significantly greater during incubation compared with the prelay period and late chick rearing. Body condition was weakly and negatively correlated with maximum and total integrated corticosterone level, indicating that some of the individual variability in stress corticosterone responses could be explained by variation in body condition. However, the largest stress response occurred during late incubation and was independent of sex, although males were in relatively poor condition and females in relatively good condition. This period coincided with the breeding stage in which energy constraints on individual adults were higher than at other periods of the reproductive cycle and birds may be physiologically primed for extended fasts.     

Sex differences in hormonal responses to social conflict in the monogamous California mouse

Monogamous species are usually considered to be less likely to exhibit sex differences in behavior or brain structure. Most previous studies examining sex differences in stress hormone responses have used relatively sexually dimorphic species such as rats. We examined the stress hormone responses of monogamous California mice (Peromyscus californicus) to resident-intruder tests. We also tested males and females under different photoperiods, because photoperiod has been shown to affect both aggression and stress hormone responses. Females, but not males showed a significant increase in corticosterone levels immediately following a resident-intruder test. Males but not females showed elevated corticosterone levels under short days. Females tested in aggression tests also showed a significant increase in plasma oxytocin levels, but only when housed in long days. This was consistent with our observation that females but not males had more oxytocin positive cells in the paraventricular nucleus (PVN) when housed under long days. Our data show that sex differences in glucocorticoid responses identified in other rodents are present in a monogamous species.     

Sex differences in cortisol secretion after administration of an ACTH analogue in sheep during the breeding and non-breeding season

The aim of this study was to compare the response of cortisol in sheep of different sex and gonadal status to adrenal cortex stimulation by an ACTH analogue in the breeding and non-breeding season. Twenty-four adult Corriedale sheep were used in the non-breeding season, and 19 in the breeding season. Three weeks prior to the first trial (non-breeding season), six rams and six ewes were gonadectomised. In each trial, blood was obtained every 15min for 9h and the animals received 0.5mg of ACTH (Tetracosactid, Synacthen Depot i.m., after 1.5h of sampling. Sampling began at 10:00a.m. in the non-breeding season and at 9:00a.m. in the breeding season. Three main effects (sex, gonadal status and season) were evaluated, each with two levels (male and female, intact and gonadectomised, breeding and non-breeding season, respectively). In both seasons, the females showed higher cortisol levels after ACTH than males (P<0.001), though the difference seemed less marked in the non-breeding season. The cortisol response in the ewes was not affected by season. The rams, however, showed a lower response in the breeding season (P<0.03). Gonadectomy reduced the response in the ewes (P<0.001) but had no effect in the rams. Nevertheless, gonadectomy also eliminated the differences between the ewes and the rams, such that the intact rams had lower levels of cortisol compared to the intact females, with those of the gonadectomised animals of both sexes being intermediate between the gonad-intact groups. The results of this study confirm sex differences in ACTH induced cortisol secretion in intact sheep in vivo. Furthermore, by applying exogenous ACTH we have directly stimulated the adrenal cortex, indicating the existence of sex differences also at this level. The circulating gonadal steroids, which are responsible at least in part for the sex differences in the responses to stress, may influence cortisol secretion from the adrenal gland by direct action at the cortex.     

Sex differences in reserve capacity of the pituitary-adrenal system in rats

Female rats exposed to complex emotional stress for 1 hour (restriction in the penal, vibration, loud dissonance music, interrupt light) simultaneously showed more considerable increases in plasma and adrenal corticosterone values than did male animals. Female rat corticosterone levels returned to basal values within 20-120 minutes of stressor-off. As for males the processes of restoration were delayed and accompanied by a 6-fold decrease in the plasma corticosterone levels compared with basal values. The response to additional acute stress (immobilization for 10 minutes) in various times after termination of complex emotional stress (0, 40, 120, 180, 240 minutes) was facilitated in females and remained unchanged in males. Plasma corticosterone levels under stressful conditions were 2-4-fold higher in females than in males. It is concluded that reserve capacity of adaptation system is significantly higher in female rats than in male ones.     

Corticosterone levels as indicators of habitat quality: effects of habitat segregation in a migratory bird during the non-breeding season

During the non-breeding season, many species of territorial migratory birds exhibit a non-random pattern of habitat distribution, with males and females occupying different habitats. In this study, we examined possible physiological consequences arising from such habitat segregation in one migrant passerine species, the American redstart (Setophaga ruticilla), on its non-breeding grounds in Jamaica, West Indies. For 2 years, we measured concentrations of corticosterone, at the time of capture (baseline) and 30 min after capture (profile of acute corticosterone secretion), in redstarts in two distinct habitats, one occupied predominately by males and one mostly by females. All redstarts in both habitat types exhibited similar concentrations of baseline corticosterone levels in fall (October), whereas in spring (March–April), redstarts in female-biased habitat exhibited significantly higher baseline levels regardless of age or sex. In fall, all individuals in both habitats exhibited significant increases in corticosterone concentration with capture and handling, but in spring only redstarts (both sexes) in male-biased habitat continued to exhibit acute corticosterone secretion. Redstarts in female-biased habitat had elevated baseline corticosterone levels and reduced acute corticosterone secretion. In spring, baseline corticosterone concentration was negatively correlated with body mass, suggesting muscle catabolism associated with high corticosterone concentrations or possibly that birds are leaner as a result of increased foraging effort. These results indicate that redstarts (primarily females) in female-biased habitats suffered a decline in physiological condition, which could in turn influence their departure schedules, migration patterns and even their condition and arrival schedules on the breeding grounds. Thus, segregation of populations into habitats of different quality during the non-breeding period may have ramifications throughout the annual cycle of such migratory species. Furthermore, these results show the usefulness of plasma corticosterone levels as indicators of physiological condition and thus habitat quality for birds during the non-breeding period. Received: 14 November 1997 / Accepted: 9 March 1998     

Sexual dimorphism of the intracellular heat shock protein 72 response.

The majority of previous work examining stress responses has been done in males. Recently, it has become clear that the impact of stressor exposure is modulated by sex. One stress response that may be affected by sex is the induction of intracellular heat shock protein (HSP) 72, which is a stress- responsive molecular chaperone that refolds denatured proteins and promotes cellular survival. The following study compared HSP72 in males and females and also examined whether the estrous cycle altered HSP72 induction in females. We hypothesized that females compared with males would have a constrained HSP72 response after an acute stressor and that the stress-induced HSP72 response in females would fluctuate with the estrous cycle. Male and female F344 rats were either left in their home cage or exposed to acute tail-shock stress (8-10/group). Immediately following stressor, trunk blood was collected and tissues were flash frozen. Vaginal smear and estrogen enzyme immunoassay were used to categorize the phase of estrous. Results show that female rats had a greater corticosterone response than males, that both males and females exhibit a stress-induced release of progesterone, and that males and females had equal levels of stress-induced circulating norepinephrine. Sexual dimorphism of the HSP72 (ELISA) response existed in pituitary gland, mesenteric lymph nodes, and liver such that female rats had an attenuated HSP72 response compared with males after stress. The adrenal glands, spleen, and heart did not exhibit sexual dimorphism of the HSP72 response. The estrous cycle did not have a significant effect on basal or stress-induced HSP72 in females.     

Sex differences in response to stress in conscious and anesthesized rats during surgical stress]

Adrenal and plasma corticosterone levels under conditions of preoperative stress (removal from animal to experimental rooms, removal from a home cage, handling, weighing and injecting with saline) were more than 2-fold higher in female rats than in male ones. Females, compared with males, showed more pronounced decrease in corticosterone responses to preoperative stress and laparotomy under nembutal anesthesia, which blocked stress-induced emotional activation. One hour after recovery from anesthesia laparotomized females but not males, demonstrated a significant (5-fold) increase in plasma corticosterone level. The absolute values of plasma corticosterone in laparotomized females, compared with males, were 2-fold lower under anesthesia but 2-fold higher after recovery from anesthesia. It is supposed that in females, compared with males, stress-induced emotional tension plays more considerable role in endocrine stress responses. This provides higher adrenocortical sensitivity to stress in conscious female rats than in male animals.     

Gonadal Steroid Hormone Receptors and Sex Differences in the Hypothalamo-Pituitary-Adrenal Axis

The rapid activation of stress-responsive neuroendocrine systems is a basic reaction of animals to perturbations in their environment. One well-established response is that of the hypothalamo-pituitary-adrenal (HPA) axis. In rats, corticosterone is the major adrenal steroid secreted and is released in direct response to adrenocorticotropin (ACTH) secreted from the anterior pituitary gland. ACTH in turn is regulated by the hypothalamic factor, corticotropin-releasing hormone. A sex difference exists in the response of the HPA axis to stress, with females reacting more robustly than males. It has been demonstrated that in both sexes, products of the HPA axis inhibit reproductive function. Conversely, the sex differences in HPA function are in part due to differences in the circulating gonadal steroid hormone milieu. It appears that testosterone can act to inhibit HPA function, whereas estrogen can enhance HPA function. One mechanism by which androgens and estrogens modulate stress responses is through the binding to their cognate receptors in the central nervous system. The distribution and regulation of androgen and estrogen receptors within the CNS suggest possible sites and mechanisms by which gonadal steroid hormones can influence stress responses. In the case of androgens, data suggest that the control of the hypothalamic paraventricular nucleus is mediated trans-synaptically. For estrogen, modulation of the HPA axis may be due to changes in glucocorticoid receptor-mediated negative feedback mechanisms. The results of a variety of studies suggest that gonadal steroid hormones, particularly testosterone, modulate HPA activity in an attempt to prevent the deleterious effects of HPA activation on reproductive function.     

The influence of sex and gonadectomy on the growth hormone and corticosterone response to hexarelin in the rat

The present study is designed to investigate the role of sex and gonadal status in the growth hormone (GH) and corticosterone response to hexarelin (HEXA), a GH-releasing peptide, which also causes a stimulatory action on the hypothalamic-pituitary-adrenal (HPA) axis. HEXA (80 microg/Kg) was administered intracarotid to anesthetized intact or gonadectomized male (ORC) and female (OVX) middle-aged rats. The GH stimulatory response to HEXA was gender-related since the GH increase was significantly (p < 0.001) higher in intact males (area under the curve, AUC= 12560 +/- 1784 ng/ml.45 min) than in females (AUC= 4628 +/- 257 ng/ml.45 min). This sex difference does not depend on circulating gonadal steroids since it persists in ORC (AUC = 11980 +/- 1136 ng/ml.45 min) and OVX (AUC = 5539 +/- 614 ng/ml.45 min) rats. The different effects of HEXA on corticosterone secretion detected in male and female rats are probably dependent on the prevailing activity of the HPA axis. In fact, in male rats that have low basal corticosterone levels, HEXA caused an increase in corticosterone secretion, which was significantly (p< 0.05) higher in ORC than in intact rats. The increase in corticosterone secretion by HEXA both in intact and OVX females was delayed, probably due to the elevated initial corticosterone levels, which could have activated the glucocorticoid negative feedback. We suggest that gender-specific patterns in the regulation of the hypothalamus-pituitary function could be responsible for the GH and corticosterone sexually differentiated responses to HEXA.     

Sex differences in lifespan extension with acarbose and 17‐α estradiol: gonadal hormones underlie male‐specific improvements in glucose tolerance and mTORC2 signaling

Interventions that extend lifespan in mice can show substantial sexual dimorphism. Here, we show that male‐specific lifespan extension with two pharmacological treatments, acarbose (ACA) and 17‐α estradiol (17aE2), is associated, in males only, with increased insulin sensitivity and improved glucose tolerance. Females, which show either smaller (ACA) or no lifespan extension (17aE2), do not derive these metabolic benefits from drug treatment. We find that these male‐specific metabolic improvements are associated with enhanced hepatic mTORC2 signaling, increased Akt activity, and phosphorylation of FOXO1a – changes that might promote metabolic health and survival in males. By manipulating sex hormone levels through gonadectomy, we show that sex‐specific changes in these metabolic pathways are modulated, in opposite directions, by both male and female gonadal hormones: Castrated males show fewer metabolic responses to drug treatment than intact males, and only those that are also observed in intact females, while ovariectomized females show some responses similar to those seen in intact males. Our results demonstrate that sex‐specific metabolic benefits occur concordantly with sexual dimorphism in lifespan extension. These sex‐specific effects can be influenced by the presence of both male and female gonadal hormones, suggesting that gonadally derived hormones from both sexes may contribute to sexual dimorphism in responses to interventions that extend mouse lifespan.     

Diurnal variations of serum testosterone levels in intact and gonadectomized male and female rhesus monkeys.

A radioimmunoassay for serum testosterone which does not require chromatographic separation was used to measure the diurnal variations in intact and orchidecomized males and intact and ovariectomized females. The intact male rhesus monkey shows a distinctive diurnal variation in serum levels of testosterone characterized by lower values during the day and a marked increase in the early evening (1900-2200 hr). The testosterone levels remain high throughout most of the lights-off period in the intact male. In contrast to the intact male, the markedly lowered serum levels of testosterone in the orchidectomized male were higher during the day and consistently showed a nadir during the early evening (2000-2200 hr). The evening nadir of testosterone levels was 51.0% lower than the 24-hr mean whereas the maximum serum level was 46.4% higher. A similar circadian pattern of testosterone was seen in both the intact and ovariectomized females. The testosterone values were higher during the day and consistently showed a nadir during the early evening. These results suggest that the adrenal secretion of testosterone varies in a diurnal pattern characterized by an early evening nadir. This adrenal pattern is overshadowed by a much larger gonadal rhythm in the intact male.     

Blood risk factor metabolites associated with heart disease and myocardial fatty acids in copper-deficient male and female rats

Intact and castrated males and intact and ovariectomized female rats were fed a copper-deficient diet in order to establish whether the protection provided in females against cardiovascular pathology and mortality is due to endogenous sex hormones, and different levels of blood lipids and/or myocardial fatty acids. Seventy-three male and female rats were assigned to a copper-deficient diet (0.6 micrograms of copper/g diet) containing 62% fructose for 8 weeks. Twelve of the male rats underwent castration and 12 of the females were ovariectomized. All animals exhibited high levels of plasma cholesterol, triglycerides, and uric acid, which were neither affected by the sex of the rat nor by the surgical treatment. The composition of fatty acids of the myocardium was similar in males and females. Except for those animals that were sacrificed by us, all other male rats died of heart pathology. In contrast, none of the female rats exhibited heart pathology and none died of the deficiency. It is suggested that heart pathology and mortality in copper deficiency are sex related and not due to high levels of plasma cholesterol, triglycerides, and uric acid or to differences in myocardial fatty acid composition.