Pituitary-ACTH Response to Metopirone and Endotoxin Administration in the Dog

Abstract

The adrenal gland production rate of cortisol during ACTH administration and the production rate of 11-desoxycortisol during Metopirone and ACTH administration were studied in a group of dogs. The plasma level of Substance S was a direct function of its adrenal production rate, whereas the plasma level of cortisol was not a direct function of the adrenal cortisol production rate. The maximal adrenal production rate of 11- desoxycortisol during Metopirone block appears to represent a major proportion of the maximal cortisol production rate without this block. Intravenous Metopirone administration over a 7-hr period did not stimulate maximal pituitary ACTH response, as a further increment in response was observed following endotoxin administration. When dogs were treated with ACTH and cortisol for 5 days and tested 36 hr after this therapy, their response to Metopirone was clearly decreased, yet their ACTH response to endotoxin was equivalent to that seen prior to therapy. Endotoxin is a more effective stimulus of ACTH release than Metopirone. Metopirone administration may provide a poor index of pituitary capacity to release ACTH in response to other stimuli.