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CARL D. MALCHOFF, JOSEPH M. HUGHES, ROBERT M. CAREY, Effect of Upright Posture on the Aldosterone Responses to Dopamine, Metoclopramide, Angiotensin II, and Adrenocorticotropin, The Journal of Clinical Endocrinology & Metabolism, Volume 65, Issue 1, 1 July 1987, Pages 203–207, https://doi.org/10.1210/jcem-65-1-203
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Aldosterone secretion in man is stimulated by potassium (K), ACTH, and angiotensin II (All) and inhibited by dopamine (DA). In normal sodium-replete supine individuals, aldosterone secretion is under maximum tonic inhibition by DA and is not inhibited further by DA administration. Sodium depletion alters plasma aldosterone responses to secretogogues. Upright posture, another physiological stimulus to aldosterone secretion, recently was demonstrated to sensitize the adrenal cortex to inhibition of aldosterone secretion by a large quantity of DA (4.0 μg/kg·min). The effect of upright posture on aldosterone responses to other secretogogues is unknown. In this study, we investigated the effect of upright posture on aldosterone responses to low infusion rates of DA, to the DA antagonist metoclopramide (M) and to All and ACTH.
Fourteen normal men eating a normal sodium diet were studied. In eight, PRA, plasma aldosterone (PAC), plasma cortisol (F), and serum K concentrations were determined after 4 h of upright posture and infusion of vehicle (D5W) or DA at 0.1, 0.4, and 2.0 μg/kg·min. Six other normal men were kept supine for 3 h and, on separate days, upright for 3 h and given iv M (10-mg bolus dose), All (1 and 4 pmol/kg·min for 30 min), and ACTH (20 and 120 mU/h for 30 min). PAC, PRA, F, and K were measured before and after these three secretogogues were administered. In the presence of vehicle, mean PAC increased by 15.1 ± 4.3 (±sem) ng/dL after 4 h of upright posture. In the presence of DA infused at 0.1, 0.4, and 2.0 μg/kg·min, the PAC response to upright posture was decreased to 9.7 ± 2.5 (P = NS), 7.5 ± 3.9 (P < 0.05), and 8.1 ± 2.0 (P < 0.05) ng/dL, respectively. This occurred without a decrease in PRA, F, or K. The stimulation of PAC 10 and 20 min after a 10-mg bolus dose of M was 9.6 ± 3.3 and 9.3 ± 2.6 ng/dL, respectively, in supine subjects and 8.3 ± 2.3 and 10.8 ± 3.4 ng/dL 10 and 20 min after the M dose in upright subjects. The responses of PAC to ACTH and All also were unchanged after 3 h of upright posture.
We conclude that upright posture sensitizes the adrenal cortex to inhibition of aldosterone secretion by DA without affecting other modifiers of aldosterone secretion. Since DA infusion rates as low as 0.4 μg/kg·min are effective, this is a specific dopaminergic action and not related to stimulation of α- or y-adrenoceptors. In contrast to the effect of sodium depletion, upright posture does not alter the aldosterone responses to any other major secretogogue.
