The adrenocortical response of greater sage grouse (Centrocercus urophasianus) to capture, ACTH injection, and confinement, as measured in fecal samples.

Investigators of wildlife populations often utilize demographic indicators to understand the relationship between habitat characteristics and population viability. Assessments of corticosterone may enable earlier detection of populations at risk of decline because physiological adjustments to habitat disturbance occur before reproductive diminutions. Noninvasive methods to accomplish these assessments are important in species of concern, such as the greater sage grouse (GRSG). Therefore, we validated a radioimmunoassay that measures immunoreactive corticosterone metabolites (ICM) in fecal samples and used it to characterize the adrenocortical response of 15 GRSG exposed to capture, intravenous injection of 50 IU/kg adrenocorticotrophic hormone (ACTH) or saline, and 22 h of confinement. Those animals injected with ACTH exhibited a more sustained (P = 0.0139) and less variable (P = 0.0012) response than those injected with saline, indicating different levels of adrenocortical activity. We also found that potential field-collection protocols of fecal samples did not alter ICM concentrations: samples held at 4 degrees C for up to 16 h contained similar levels of ICM as those frozen (-20 degrees C) immediately. This study demonstrates a multiphasic adrenocortical response that varied with the level of stimulation and indicates that the assay used to measure this phenomenon is applicable for studies of wild GRSG.

Social suppression of cortisol in female marmoset monkeys: role of circulating ACTH levels and glucocorticoid negative feedback.

Behaviorally subordinate female common marmoset monkeys (Callithrix jacchus) exhibit pronounced, chronic reductions of circulating cortisol levels. Cortisol suppression in these animals is mediated in part by adrenocortical hyporesponsiveness to adrenocorticotropic hormone (ACTH). In addition, we hypothesized that social subordination may activate a central, neurally mediated mechanism to further inhibit hypothalamo-pituitary-adrenal function. In this study, therefore, we evaluated basal plasma cortisol and ACTH concentrations, as well as cortisol and ACTH responses to dexamethasone (DEX), in dominant and subordinate females to initially characterize such a mechanism. Morning plasma cortisol and ACTH levels were determined before, and 1, 2, and 3 days following administration of DEX (0.5, 1.0, or 5.0 mg/kg, IM) or saline. Baseline cortisol concentrations prior to DEX treatment were significantly lower in subordinate females than in dominants, as previously reported. However, ACTH concentrations in the same blood samples did not differ between the two groups. Furthermore, dominant and subordinate females showed similar cortisol and ACTH responses to DEX. These results indicate that reduced circulating cortisol levels in subordinate females are not associated with either altered circulating ACTH concentrations or enhanced responsiveness to glucocorticoid negative feedback. However, the finding that basal ACTH levels are not elevated in subordinate females as compared to dominants, in spite of low circulating cortisol concentrations, suggests that ACTH secretion in subordinate females is restrained by a steroid-independent inhibitory mechanism operating at the level of the brain or pituitary.

Seasonal and social correlates of fecal testosterone and cortisol levels in wild male muriquis (Brachyteles arachnoides).

Fecal testosterone and cortisol levels were analyzed from six wild male muriquis (Brachyteles arachnoides) over a 19-month period at the Estação Biológica de Caratinga in Minas Gerais, Brazil, to investigate the hormonal correlates of seasonal sexual behavior and environmental conditions. Group mean testosterone levels based on weekly samples from the six males did not differ between copulatory and noncopulatory periods or between rainy and dry seasons. Cortisol levels did change with copulatory periods, and were significantly higher during the second dry season, when mating continued following an exceptionally heavy rainy season, than during the first dry season, when mating ceased. Males exhibited individual variation in the timing of their hormone shifts relative to their sexual activity, but neither hormone levels nor sexual activity were related to male age. Despite individual differences in the timing of testosterone fluctuations around the onset and offset of the copulatory season, all males exhibited elevated cortisol concentrations following a slight increase in testosterone at the beginning of the copulatory season. Both the lack of significant changes in testosterone levels with the onset of the rainy and copulatory season and the lack of prebreeding increases in cortisol may be related to the low levels of overt aggression displayed by male muriquis over access to mates.

Suppression of cortisol levels in subordinate female marmosets: reproductive and social contributions.

Socially subordinate female common marmosets (Callithrix jacchus) have markedly lower plasma cortisol levels than dominant females. Subordinate females also undergo hypoestrogenemic anovulation, and estrogen can elevate glucocorticoid levels. Therefore, we previously hypothesized that this cortisol difference is mediated by rank-related differences in reproductive hormones, probably estradiol. To test this possibility, we characterized the effects of the ovarian cycle and ovariectomy on plasma cortisol concentrations. Beginning in the early follicular phase, basal blood samples were collected from seven cycling female marmosets daily for 16 days and at 2- to 3-day intervals for another 16 days. Samples were collected identically from seven anovulatory subordinate females and seven long-term ovariectomized females. Cortisol levels changed reliably across the ovarian cycle, with levels in the mid- to late follicular, peri-ovulatory, and early luteal phases higher than those in the remainder of the cycle. Cortisol levels of cycling females were significantly higher than those of subordinates at all parts of the cycle, but were significantly higher than those of ovariectomized females only during the midcycle elevation. Unexpectedly, subordinates had significantly lower cortisol levels than ovariectomized females, as well as higher estradiol and estrone levels and lower progesterone and luteinizing hormone (LH) levels. These results confirm that circulating cortisol concentrations are modulated by reproductive function in female marmosets but also indicate that low cortisol levels in subordinate females cannot be attributed simply to hypoestrogenemia. Instead, other factors, such as direct effects of social subordination or suppression of LH levels, contribute to suppression of cortisol in subordinates.

Metabolism of reproductive steroids during the ovarian cycle in two species of callitrichids, Saguinus oedipus and Callithrix jacchus, and estimation of the ovulatory period from fecal steroids.

Gonadal steroids were measured in daily fecal samples providing comparative data on steroid metabolism in two genera of New World primates. Circulating bioactive LH and progesterone concentrations and fecal progesterone, pregnanediol, estradiol, and estrone concentrations were measured by collecting blood and daily fecal samples from four captive common marmoset females and four cotton-top tamarin females for 30 days. High recoveries (> 80%) of labeled steroids that were added directly to the feces before extraction were recovered from feces of both species. Because of the presence of complex steroid conjugates, only one fifth the amount of estradiol was measured without solvolysis as compared to the amount measured with solvolysis. In tamarins, steroids were metabolized rapidly, with all postovulatory increases occurring within two days after the circulating LH peak (an increase of 2 SD higher than mean follicular levels). In marmosets, steroid excretion was slower; increased steroid levels occurred 2-4 days after the LH peak except in the case of estrone, which did not consistently increase after the LH peak. Circulating estrone and estradiol both contributed to the high excretion of estradiol in the feces from both species. The timing in the delay in excretion of fecal steroids was used to accurately determine the ovulatory period to within a 2-day window. This degree of accuracy is possible when the duration of the delay to the LH peak is known for a given species. Additionally, steroid concentrations were highly correlated between frozen and lyophilized fecal samples (0.81 +/- 0.07 SEM), indicating that fluid removal from the feces did not effectively alter steroid profiles.

Long-term effects of prenatal stress on HPA axis activity in juvenile rhesus monkeys.

The effect of stress to the pregnant mother on hormonal responses of the offspring to stressful events was investigated in juvenile rhesus monkeys. Six pregnant monkeys were repeatedly removed from their home cages and exposed to unpredictable noise during mid- to late gestation (Days 90-145 postconception), while six undisturbed pregnant mothers served as controls. Blood samples were collected from the juvenile offspring under anesthesia on four occasions and assayed for ACTH and cortisol. In a second experiment, blood samples were collected from the awake offspring under a baseline and four progressively stressful conditions. Offspring of stressed mothers showed higher ACTH and cortisol levels than control offspring at all four anesthesia samples and at a nonanesthesized home cage baseline. Prenatally stressed offspring also showed higher ACTH values in all four stress conditions. Cortisol values were similar for the two groups under the stress conditions. The disparity between the two groups in the relationship between ACTH and cortisol was greatest in the most stressful condition, suggesting regulatory differences between the two groups. These results indicate that offspring of primate mothers stressed during pregnancy show enhanced HPA axis responsivity to stressors later in life, and concur with rodent findings indicating that prenatal stress may have long-term effects on HPA axis regulation.