Hypoestrogenism does not mediate social suppression of cortisol in subordinate female marmosets

Behaviorally subordinate female marmosets undergo social suppression of ovulation and hypoestrogenism, as well as chronic reductions in circulating basal cortisol concentrations. Because estrogen elevates hypothalamic-pituitary-adrenal axis activity and circulating glucocorticoid levels in other species, we tested the hypothesis that socially induced hypoestrogenism contributes to cortisol reductions in subordinate female marmosets. We characterized morning basal plasma cortisol levels, as well as cortisol responses to exogenous adrenocorticotropic hormone (ACTH; 0, 1, or 10 microg/kg), in seven anovulatory subordinate females and six ovariectomized, non-subordinate females under two conditions: during long-term treatment with estradiol (E2) and control. Circulating E2 and cortisol levels were compared to those of six dominant females undergoing ovulatory cycles. Basal cortisol concentrations in the control condition were significantly lower in subordinates than in both dominant and ovariectomized females. E2 treatment elevated circulating E2 levels of subordinate and ovariectomized females into the range seen in dominant females but did not increase either mean basal or ACTH-stimulated cortisol levels. To the contrary, E2 treatment caused a decline in basal cortisol levels over time, especially in ovariectomized animals. These results indicate that treatment with exogenous estrogen does not elevate circulating cortisol levels in previously hypoestrogenemic female marmosets and, correspondingly that socially induced hypoestrogenism does not diminish cortisol levels in subordinate females.