The effect of atrial natriuretic peptide (ANP), before and after converting enzyme (CE) inhibition, was investigated in six primary hypertensive patients taking a constant diet. In this placebo-controlled, single-blind, randomized study, the patients received, on three different days, i.v. infusions of (a) placebo, or (b) a-human ANP, 150 μg over 30 min, or (c) α-human ANP after acute CE inhibition by enalapril (EN) 20 mg P.O., 4 h before ANP infusion. ANP infusion increased urinary sodium (p < 0.001) and volume excretion. Blood pressure (BP), heart rate, stroke volume and shortening fraction (echocardiography), plasma renin activity (PRA), and plasma aldosterone did not change significantly. Urinary norepinephrine and dopamine were significantly in-creased (p < 0.05) after ANP infusion. BP was significantly reduced after EN in every patient (p < 0.05). ANP infusion during CE inhibition induced a more sustained increase of sodium excretion and diuresis with respect to ANP infusion alone (p < (1.05). PRA was significantly reduced while no further reduction of BP was observed. These data suggest that CE inhibition may increase the natriuretic and diuretic effect of ANP in hypertensive patients.
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