Plasma cortisol response to ACTH does not accurately indicate the state of hypothalamic-pituitary-adrenal axis.

The hypothalamic-pituitary-adrenal function was studied in 55 patients with various pituitary disorders. In particular, the consistency between the responses of plasma cortisol to exogenous ACTH and to insulin hypoglycemia was investigated in 5 patients in whom cortisol response to insulin was absent; four of these patients showed a cortisol response to ACTH of variable degree. These 4 patients had surgical or functional hypothalamus-pituitary disconnection and showed a preserved cortisol response to lysine vasopressin. These data demonstrate the unreliability of ACTH test in assessing hypothalamic-pituitary-adrenal function in hypopituitary patients.