To evaluate the humoral and hemodynamic (both systemic and renal) effects of celiprolol and to assess whether these effects are at least partially due to the activation of dopamine (DA) receptors, 9 out-patients with mild to moderate uncomplicated essential hypertension, without any therapy for at least 3 weeks, received celiprolol (400 mg once daily) and placebo, each for 1 month, according to a double-blind randomized trial pattern. At the end of each treatment period, blood pressure, heart rate, renal plasma flow, glomerular filtration rate, plasma renin activity, plasma aldosterone and plasma norepinephrine were measured after administration of saline solution and intravenous metoclopramide. Compared with placebo, celiprolol significantly reduced mean blood pressure, heart rate and plasma norepinephrine. Plasma renin activity showed a tendency toward a reduction during celiprolol treatment, which was not associated with changes in plasma aldosterone. Despite the decrease in mean blood pressure, renal plasma flow did not change, so that renovascular resistances were significantly reduced. Glomerular filtration rate was unchanged and the filtration fraction showed a trend toward a reduction during celiprolol treatment. Percent decrements of renovascular resistances and of mean blood pressure induced by celiprolol tended to correlate with changes in plasma norepinephrine. Metoclopramide did not influence the hemodynamic (systemic and renal) effects of celiprolol nor plasma renin activity and plasma norepinephrine, and it increased aldosterone levels to a similar extent before and after administration of celiprolol.(ABSTRACT TRUNCATED AT 250 WORDS)