Increased Cortisol Secretion after Small Hemorrhage Is Not Attributable to Changes in Adrenocorticotropin*

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Abstract
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 .cntdot. 3 min) or 20 ml/(kg .cntdot. 3 min) hemorrhage. All 4 variables increased substantially after 20 ml/(kg .cntdot. 3 min) hemorrhage. Secretion rates of cortisol and corticosterone increased significantly after 10 ml/(kg .cntdot. 3 min) hemorrhage, without a change in ACTH. The responses of ACTH and the secretion rates of cortisol to 10 ml/(kg .cntdot. 3 min) hemorrhage and i.v. infusion of ACTH were compared. Infusions of ACTH required to match the secretory response of cortisol after 10 ml/(kg .cntdot. 3 min) hemorrhage resulted in concentrations of ACTH significantly higher than those observed after 10 ml/(kg .cntdot. 3 min) hemorrhage. Apparently 10 ml/(kg .cntdot. 3 min) hemorrhage induces an acute increase in adrenocortical sensitivity to ACTH.