DOPAMINERGIC SUPPRESSION OF ANGIOTENSIN-II-INDUCED ALDOSTERONE SECRETION IN MAN - DIFFERENTIAL RESPONSES DURING SODIUM LOADING AND DEPLETION

Aldosterone secretion may be inhibited by dopaminergic mechanisms in man. Dopamine does not inhibit aldosterone responses to angiotensin II in Na replete normal subjects. Since Na deficiency is associated with a reduction in renal dopamine formation, the effect of dopamine on angiotensin II-induced aldosterone secretion in the Na-depleted state. Six normal subjects in balance at 10 meq-Na intake (UNaV 17 .+-. 2 meq/24 h) received dopamine 4 .mu.g/kg per min or vehicle for 210 min on 2 consecutive days. After 60 min of the dopamine or vehicle infusion, the subjects received successive 30 min infusions of angiotensin II in increasing doses of 0.5, 1, 2, 4 and 6 picomol/kg per min. Control plasma aldosterone concentrations before vehicle or dopamine were 15 .+-. 3 (mean 1 .+-. SE) and 25 .+-. 3 ng/dl, respectively. Aldosterone responses to angiotensin II were greater with vehicle than dopamine at angiotensin II doses of 4 and 6 picomol/kg per min (P < 0.025). The slope of angiotensin-aldosterone dose-response curve was steeper with vehicle (0.33) than with dopamine (0.16), P < 0.01. Serum prolactin concentrations were lower with dopamine (1.6 .+-. 0.8 ng/ml) than with vehicle (6.4 .+-. 1.2 ng/ml, P < 0.05) by 120 min of infusion and remained suppressed with dopamine for the remainder of the dopamine infusion. Diastolic blood pressure was higher (P < 0.05) with vehicle than with dopamine at angiotensin II doses of 2,4 and 6 picomol/kg per min. Dopamine administration was associated with an increase in plasma cortisol concentration from 90 to 150 min of infusion (P < 0.05). The same 6 subjects in balance at 300 meq Na intake (UNaV 287 .+-. 18 meq/24 h) had no difference in aldosterone response or slope of the angiotensin II-aldosterone dose-response curve with dopamine or vehicle. Serum prolactin concentrations were lower with dopamine (5.4 .+-. 1.2 ng/ml) than with vehicle (9.3 .+-. 1.4 ng/ml, P < 0.05) by 90 min of infusion and remained suppressed for the rest of the study. Cortisol levels were significantly higher with dopamine than with vehicle from 120-150 min of infusion (P < 0.05). In conclusion, dopamine inhibits angiotensin II-stimulated aldosterone secretion during Na deficiency in man.