MARKED DIFFERENCES IN FUNCTIONING OF THE HYPOTHALAMIC-PITUITARY-ADRENAL AXIS BETWEEN GROUPS OF MEN

To compare profiles of hypothalamic-pituitary-adrenal (HPA) responsive ness, healthy, moderately trained men (n = 15) were classified as high (n = 7) or low responders (n = 8) on the basis of plasma adrenocortic otropic hormone (ACTH) responses to strenuous treadmill exercise 4 h a fter 4 mg of dexamethasone (Dex). These groups were then evaluated to compare 1)HPA and growth hormone responses to exercise at 90% maximal gen uptake 4 h after placebo, Dex (4 mg), and hydrocortisone (100 mg); 2) pituitary-adrenal responses to infusion of arginine vasopressin (A VP); 3) plasma cortisol after a Dex suppression test (1 mg); and 4)beh avioral characteristics. In comparison to low responders, high respond ers exhibited significantly 1) higher plasma ACTH responses to exercis e after placebo and Dex; 2) higher plasma AVP secretion with exercise after placebo and marked Dex- and hydrocortisone-induced enhancement o f exercise-induced AVP secretion; 3) lower Dex-induced increases in ba sal and stimulated growth hormone secretion; 4) higher plasma ACTH res ponses to infusion of AVP; and 5) a trend (P = 0.09) for higher trait anxiety ratings. Similar suppression of plasma cortisol was noted afte r 1 mg Dex. We conclude that subgroups of healthy male volunteers exhi bit unique profiles of HPA responsiveness. We also believe that glucoc orticoid pretreatment combined with strenuous exercise allows function al HPA responsiveness to be distinguished between subgroups of healthy controls and may be useful in the determination of susceptibility dis orders characterized by hyper- and hypo-HPA activation.