Reduced adrenocortical responsiveness to adrenocorticotropic hormone (ACTH) in socially subordinate female marmoset monkeys

Socially subordinate female common marmoset monkeys undergo pronounced, chr onic reductions in basal plasma cortisol levels, which appear to result bot h from socially induced suppression of reproductive hormones and from direc t effects of social subordination. In this study, we tested the hypothesis that this cortisol suppression is mediated by reduced adrenocortical respon siveness to adrenocorticotropic hormone (ACTH). Dominant, subordinate, and ovariectomized females were given dexamethasone (5 mg/kg, IM), followed the next morning by human ACTH(1-39) (10 mu g/kg, IV) or sterile saline (0.5 m l/kg, IV); blood samples were collected at -20 through 150 min from ACTH or saline treatment and assayed for cortisol. ACTH, but not saline, caused a marked elevation of plasma cortisol levels. Prior to ACTH treatment, domina nt females tended to have higher dexamethasone-suppressed cortisol levels t han subordinate and ovariectomized females. After ACTH treatment, dominant females had significantly higher cortisol concentrations, as well as higher peak and net integrated cortisol responses to ACTH, than did subordinate a nd ovariectomized animals; the latter two groups showed comparable cortisol responses to ACTH. These results suggest that dampened adrenocortical resp onsiveness to ACTH contributes to chronic reductions in cortisol levels in subordinate female marmosets and may be mediated by suppression of reproduc tive hormones. (C) 2000 Elsevier Science Ltd. All rights reserved.