Increased cortisol secretion after small hemorrhage is not attributable to changes in adrenocorticotropin.

Adrenal secretory rates of cortisol and corticosterone and arterial concentrations of ACTH and cortisol were measured in conscious trained dogs subjected to 10 ml/(kg . 3 min) or 20 ml/(kg . 3 min) hemorrhage. All four variables increased substantially after 20 ml/(kg . 3 min) hemorrhage. Secretion rates of cortisol and corticosterone increased significantly after 10 ml/(kg . 3 min) hemorrhage, without a change in ACTH. The responses of ACTH and the secretion rates of cortisol to 10 ml/(kg . 3 min) hemorrhage and iv infusion of ACTH were compared. Infusions of ACTH required to match the secretory response of cortisol after 10 ml/(kg . 3 min) hemorrhage resulted in concentrations of ACTH significantly higher than those observed after 10 ml/(kg . 3 min) hemorrhage. These results suggest that 10 ml/(kg . 3 min) hemorrhage induces an acute increase in adrenocortical sensitivity to ACTH.