Lack of coupling between adrenal cortical metabolic activity and blood flow in anesthetized dogs

Abstract

To determine whether adrenal O2 consumption and cortical blood flow (CBF) increase during stimulation of cortical secretory activity, exogenous adrenocorticotrophic hormone (ACTH) was infused at 0, 2, and 10 ng.kg-1.min-1 (groups 1, 2, and 3, respectively) into dexamethasone-pretreated, pentobarbital-fentanyl-anesthetized, ventilated dogs. ACTH levels of approximately 20, 100, and 500 pg/ml were obtained in groups 1, 2, and 3, respectively. Cortisol secretion increased after 20 min in groups 2 and 3 (from 0.016 +/- 0.004 to 2.25 +/- 1.36 and from 0.02 +/- 0.01 to 5.32 +/- 1.23 microgram.min-1.g cortex-1, respectively) while adenosine 3',5'-cyclic monophosphate (cAMP) secretion increased after 20 min only in group 3 (from 5.7 +/- 2.8 to 61.3 +/- 18.6 micrograms.min-1.g cortex-1). Whole adrenal gland O2 consumption increased after 20 min in group 3 animals (from 0.89 +/- 0.16 to 1.77 +/- 0.27 ml O2.min-1.100 g tissue-1) but not in the other two groups. CBF measured with radiolabeled microspheres was unaffected by ACTH infusion while O2 extraction increased from a baseline of 5.9 +/- 1.4 to 13.0 +/- 2.4% after 30 min in group 3. These data demonstrate that in anesthetized dogs increases in adrenal cortical secretory activity are associated with increases in O2 consumption, and this increase in O2 consumption is met by increasing O2 extraction, not by increasing cortical blood flow.