Propylbutyldopamine. Mechanism of blood pressure lowering in hypertensive patients.

The effects of propylbutyldopamine ( PBDA ), an analog of dopamine lacking significant vasoconstrictor effects, were examined in seven patients with essential hypertension. Cardiovascular hemodynamics, renal plasma flow, urinary sodium excretion, and the renin-angiotensin-aldosterone system were examined during PBDA infusion both before and after administration of low (8 micrograms/kg) and high (40 micrograms/kg) doses of the dopamine receptor antagonist metoclopramide. Infusion of PBDA at a rate of 20 micrograms/kg/min lowered mean arterial pressure from an average control value of 112 +/- 4 to 94 +/- 3 mm Hg during the last 5 minutes of infusion (p less than 0.01), and increased effective renal plasma flow from 330 +/- 22 ml/min to 591 +/- 46 ml/min (p less than 0.01). Changes in heart rate (+ 16% +/- 5% increase from control values of 77 +/- 3 bpm), urinary sodium excretion (+ 13% +/- 5% increase from control value of 121 +/- 11 muEq/min), plasma renin activity (+ 23% +/- 15% increase over control value of 1.3 +/- 0.3 ng angiotensin I/ml/hr), and plasma aldosterone (+ 26% +/- 12% increase over control value of 17 +/- 6 ng/dl) accompanied PBDA infusion. Pretreatment with metoclopramide at a dose of 8 micrograms/kg prior to PBDA infusion partially blunted the blood pressure reduction produced by PBDA alone (-10% +/- 8% vs -20% +/- 4% compared to control values, p less than 0.1) but had no effect on PBDA -induced increases in renal plasma flow (+ 179% +/- 15% vs + 179% +/- 9% compared to control).(ABSTRACT TRUNCATED AT 250 WORDS)