Effect of an alpha- and beta-adrenoceptor-blocking agent (labetalol) on haemodynamics in hypertension.

1 The effect of an intravenous bolus of labetalol (0.6--1.6 mg/kg body weight) on central and peripheral haemodynamics was studied in nine subjects with essential hypertension and in eleven subjects with chronic renal disease and hypertension. 2 The BP reduction amounting to 20/13 mmHg was entirely due to the lowering of the total peripheral vascular resistance. This also included the vascular resistance in the muscles. 3 This peripheral vasodilatation was not counteracted by a reflex increase of the cardiac output. 4 The reflex tachycardia and overshoot of BP in Valsalva's manoeuvre were largely abolished. 5 Central and peripheral venous BPs, vascular volume of the forearm and venous distensibility did not show any significant change after treatment with labetalol. 6 In spite of the lowering of the vascular resistance of the forearm by labetalol, forearm blood flow was not significantly affected due to the parallel decrease in the perfusion pressure. 7 Plasma renin activity fell after labetalol in all instances.