Plasma aldosterone, 18-hydroxycorticosterone (18-OH-B), 18-hydroxydeoxycorticosterone (18-OH-DOC), corticosterone, cortisol and prolactin levels were determined during an angiotensin II infusion at increasing rates both with and without a simultaneous infusion of dopamine in seven normotensive subjects, in ten patients with essential hypertension, and in ten patients with primary aldosteronism. In a second set of experiments, maximum increases of these plasma levels were determined after metoclopramide (10 mg intravenously) in all subgroups. As compared with the other groups, an exaggerated angiotensin II-induced response of plasma aldosterone and 18-OH-B levels was observed in the five patients with low-renin essential hypertension (LREH) and in five patients with idiopathic hyperaldosteronism (IHA). Dopamine reduced the maximal increase of aldosterone and of 18-OH-B after angiotensin II to 259 +/- 48 (SEM) pg/ml and 511 +/- 152 pg/ml respectively in LREH (without dopamine: 515 +/- 74 and 908 +/- 201 respectively; P less than 0.05), and to 466 +/- 197 and 741 +/- 212 in IHA (without dopamine: 766 +/- 193 and 1264 +/- 337 respectively; P less than 0.05). The maximal increases of plasma aldosterone, 18-OH-B, and prolactin after metoclopramide (10 mg intravenously) were higher (P less than 0.01) in patients with LREH and in patients with primary aldosteronism. Plasma levels of 18-OH-DOC, corticosterone and cortisol were not affected by the stimuli applied. The exaggerated response to metoclopramide as well as to angiotensin II and its reversion only by pharmacological doses of dopamine are consistent with an increased but ineffective dopamine inhibition of aldosterone and 18-OH-B in LREH and IHA.