Splanchnic Nerve Stimulation Modulates Steroid Secretion in Hypophysectomized Dogs

Abstract

To test whether or not splanchnic neural input to the adrenal gland affects secretion of steroids from the adrenal cortex, the thoracic splanchnic nerve was electrically stimulated in pentobarbital-anesthetized dogs after hypophysectomy and replacement with physiological concentrations of ACTH. An adrenal vein cannula was placed to permit measurement of cortisol, corticosterone, 11 -deoxycortisol, epinephrine and norepinephrine secretion rates and adrenal blood flow. Plasma ACTH was measured and the presentation rate of ACTH was calculated as the product of plasma ACTH concentration and adrenal plasma flow. Dogs were infused initially with ACTH for 60 min at 2 ng/min followed by infusion for 60 min at 10 ng/min. Within each infusion period, the distal end of the nerve was stimulated (20 V; 0.5-ms pulse duration) at 4 and at 20 Hz for 10 min each. Nerve stimulation resulted in a frequency-dependent increase in mean arterial pressure, in epinephrine and norepinephrine secretion and in adrenal blood flow. Arterial ACTH remained constant during nerve stimulation; however, increased adrenal blood flow resulted in increased presentation rate of ACTH to the adrenal. Cortisol secretion increased in response to nerve stimulation at 4 and 20 Hz during infusion of 2 and 10 ng/min ACTH and occurred prior to changes in presentation rate of ACTH. Corticosterone secretion also increased after stimulation at both frequencies, but the response was observed only during infusion of 10 ng/min ACTH. In contrast, 11-deoxycortisol decreased after nerve stimulation at 4 Hz but showed no response after stimulation at 20 Hz during infusion of 2 and 10 ng/min ACTH. Steroid ratios were calculated to assess the possible involvement of specific steroidogenic enzymes in the observed responses. The cortisol to 11-deoxycortisol ratio was increased, whereas the cortisol to corticosterone ratio was not affected by nerve stimulation, suggesting a change in 11-β-hydroxylase activity. These data show that splanchnic nerve stimulation can increase cortisol secretion independently of changes in arterial ACTH. The effect of splanchnic nerve activity on cortisol secretion may result from increasing vascular delivery of ACTH to the adrenal, from release of a non pituitary humoral factor with steroidogenic activity or from direct stimulation of steroidogenesis by an adrenal neurotransmitter substance.