Surgery Potentiates Adrenocortical Responses to Hypoxia in Dogs

Abstract

We studied the effect of prior surgery on the ACTH and corticosteroid responses to acute hypoxia. Five conditioned, pentobarbital-anesthetized, gallamine-paralyzed mongrel dogs were exposed to 24 min of isocapnic hypoxia (11% O2/89% N2) 2 hr (Expt I) and approximately 1 week (Expt II) after implantation of femoral arterial and venous catheters. ACTH and corticosteroid responses were assessed by RIA of arterial plasma samples. Arterial PO2 fell similarly in both experiments from 82 to 26 Torr. This caused significant increases in ACTH of similar magnitude in both experiments. Corticosteroid levels increased more in Expt I than Expt II indicating an apparent potentiation by surgery of the adrenocortical response to hypoxia. Two additional dogs were studied in reverse order under lighter anesthesia such that ACTH and corticosteroid levels after surgery were higher than in the first set of experiments. Under these conditions, hypoxia still produced a large increase in ACTH and corticosteroids after acute surgery. Correlation of log ACTH with corticosteroid levels (adrenal dose response) revealed a significant increase in slope in dogs with acute surgery suggesting that surgery interacted with hypoxia either to change the metabolic clearance rate of corticosteroid or to increase adrenal sensitivity to ACTH.