Temporal effects of ACTH, indomethacin and 7-oxa-13-prostynoic acid upon glucocorticoid production by the human adrenal

Role of prostaglandins in the aldosterone response to ACTH in sodium depleted human subjects

It is well established that the response of plasma aldosterone to ACTH is enhanced in the sodium depleted state. The mechanisms for this phenomenon are not clear, however, and the present study was undertaken to determine the possible participation of endogenous prostaglandins. ACTH, 250 ug by i.m. administration, was given to 10 human subjects pretreated in four different ways: 1. Control, receiving a 200 mEq per day sodium diet; 2. Sodium depletion (60 mEq/day sodium plus furosemide) plus indomethacin; 3. Sodium depletion plus indomethacin plus captopril; and 4. Sodium depletion plus captopril. Only in the last group, in which the prostaglandin cyclooxygenase inhibitor, indomethacin, was not given during the sodium depletion, did an exaggerated aldosterone response to ACTH occur (an increase of 468% compared with an increase of 182% during control, P less than 0.005). The angiotensin converting enzyme inhibitor, captopril, did not effect this response. Thus, endogenous prostaglandins appear to be of far greater importance than the renin-angiotensin system in mediating the increased aldosterone response to ACTH administration during the sodium depleted state in man.

Corticosterone secretion after inhibition of prostaglandin synthesis by indomethacin

Systemic indomethacin (Ind) administration decreased prostaglandin F (PGF) content of the rat adrenal to less than 1.4 pg/mg. This was less than 5% of the adrenal PGF content in the gelatin-treated (Gel) control group (34 pg/mg). Basal plasma corticosterone levels were increased by the Ind treatment. Since the calculated metabolic clearance rate for corticosterone was unchanged, this increase was attributed to an enhanced adrenal secretion rate that was secondary to elevated plasma ACTH concentration. Ether exposure in the presence of Ind did not stimulate a normal rise in plasma corticosterone or adrenal corticosteroidogenesis. Adrenal responsiveness to exogenous ACTH was reduced after Ind treatment. There was a normal rise in plasma ACTH levels following ether exposure confirming the adrenal as the site of inhibition. Systemic Ind treatment thus appears to have two sites of action in altering plasma corticosterone levels: 1) a direct effect on the adrenal, inhibiting normal secretion in response to acute elevations of plasma ACTH, and 2) an action at the pituitary or hypothalamic level, eliciting an increase in basal ACTH secretion.

The failure of indomethacin to alter ACTH-induced adrenal hyperaemia or steroidogenesis in the anaesthetized dog

1 The response of adrenal blood flow to adrenocorticotropic hormone (ACTH) was measured with radioactive microspheres in anaesthetized, dexamethasone-treated, mongrel dog. 2 Adrenocorticotropic hormone (2 u/h i.v.) increased adrenal blood flow within 15 min and this persisted for the duration of the infusion. 3 Cortisol concentrations also rose with ACTH infusion. 4 Indomethacin (6 mg/kg i.v. followed by 1 mg/min) did not effect the adrenal response to ACTH although plasma concentrations of indomethacin (21.9 +/- 2.5 micrograms/ml) adequate to suppress prostaglandin synthesis were achieved. 5 We conclude that prostaglandins are not required for steroidogenesis or the adrenal haemodynamic response to ACTH.