Dopaminergic Modulation of 18-Hydroxycorticosterone Secretion in Man

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Abstract
This study was designed to investigate mechanisms of dopaminergic control of corticosteroid secretion and to determine on which step in the aldosterone biosynthetic pathway dopamine exerts its effects. Plasma concentrations of electrolytes, PRA, plasma cortisol, 11-deoxycorticosterone, corticosterone (18-OHB), and 18-hydroxy-ll-deoxycorticosterone were not altered by the iv administration of 10 mg metoclopramide in six healthy male volunteers. Metoclopramide increased plasma aldosterone from 6.3 ± 0.9 ng/dl to a maximum of 23.0 ± 3.4 ng/dl, plasma 18-OHB from 11.4 ± 1.1 ng/dl to a maximum level of 42.8 ± 4.4 ng/dl, and PRL from 9.9 ± 1.4 ng/ml to a maximum of 71.0 ± 5.5 ng/ml. The aldosterone and 18-OHB responses displayed a parallel time course, with significant responses of both occurring within 5 min after metoclopramide administration. Dopamine infusions (3 μg/kg-min) begun 60 min before the administration of metoclopramide markedly decreased the 18- OHB as well as the aldosterone and PRL responses to the dopamine antagonist. A parallel time course of stimulation of 18- OHB and aldosterone secretion with no change in other aldosterone precursors suggests that dopamine may modulate the activity of the glomerulosa 18-hydroxylase enzyme. Thus, rather than simply affecting aldosterone secretion, dopaminergic mechanisms appear to modulate the biosynthesis of aldosterone.