Effect of the serotonin-4 receptor agonist zacopride on aldosterone secretion from the human adrenal cortex: in vivo and in vitro studies.

We have recently shown that serotonin (5-HT) stimulates cortisol secretion from human adrenocortical tissue in vitro through activation of 5-HT4 receptors. The aim of the present study was to investigate the effect of the 5-HT4 agonist racemic zacopride on aldosterone secretion from the human adrenal gland in vivo and in vitro. In vivo studies were conducted on 28 healthy volunteers pretreated with dexamethasone. The subjects received a single oral dose of placebo, 10 micrograms zacopride, or 400 micrograms zacopride. Plasma aldosterone levels increased significantly within 90 min after the administration of 400 micrograms zacopride, remained elevated for 60 min, and gradually returned to the baseline within 180 min. In contrast, the administration of 10 micrograms zacopride or placebo did not modify the aldosterone concentration. No significant changes were observed in renin, ACTH, or cortisol levels. In vitro studies were conducted on perifused human adrenocortical slices. Administration of 20-min pulses of zacopride (from 10(-11) - 10(-6) mol/L) induced a dose-dependent increase in aldosterone secretion. The minimal effective dose was 10(-10) mol/L, and half-maximal stimulation was obtained with a dose of 7 x 10(-8) mol/L. Zacopride was 100 times more potent in stimulating aldosterone than cortisol release. Taken together, the present data suggest that 5-HT-evoked aldosterone secretion involves the activation of 5-HT4 receptors.