Acute and chronic hemodynamic effects of drugs with different actions on adrenergic receptors: a comparison between alpha blockers and different types of beta blockers with and without vasodilating effect

Abstract

The regulation of vascular resistance, cardiac output, and thus blood pressure can be influenced by antihypertensive drugs acting at central and peripheral adrenergic receptors. The results presented here are from acute or chronic studies in 205 patients with mild or moderately severe essential hypertension: beta blockers (N = 101); alpha blockers (N = 36); a separate alpha- + beta-blocker combination or the combination agent labetalol (N = 37); prizidilol, a beta-blocker/vasodilator (N = 14); and dilevalol, a beta blocker/beta 2-stimulator (N = 17). Beta blockers without strong intrinsic sympathomimetic activity reduce heart rate and cardiac output immediately, but due to a reflex increase in total peripheral resistance index, blood pressure is unchanged or only slightly reduced. During chronic use, total peripheral resistance drops towards pretreatment level and pressure falls. Beta blockers with strong intrinsic sympathomimetic activity do not reduce heart rate or cardiac output at rest when sympathetic tone is low. During exercise, heart rate and cardiac output are reduced, but less than with conventional beta blockers, and resistance is unchanged or slightly reduced. An acute and chronic reduction in blood pressure can be produced by alpha-adrenergic receptor blockers (prazosin, doxazosin, trimazosin), and in these cases the fall occurs via a reduction in total peripheral resistance index without reflex tachycardia. These drugs tend to increase exercise stroke volume and cardiac output during chronic treatment. Free combinations of beta and alpha blockers or the use of the fixed combination drug, labetalol, induce marked reductions in blood pressure at rest and during exercise, mainly through a reduction in total peripheral resistance index. During chronic treatment, exercise stroke volume and cardiac output are well maintained. In acute studies with dilevalol, systolic blood pressure, diastolic blood pressure, and mean arterial pressure were reduced (p less than 0.001) within 1 hour in 17 males with essential hypertension (WHO stage I) who received 200-400 mg oral dilevalol. The reduction in MAP was around 16-17% and was associated with an immediate fall in the total peripheral resistance index of the same magnitude (14%, p less than 0.001) after 1 hour at rest. There were no significant changes in heart rate or cardiac index.(ABSTRACT TRUNCATED AT 400 WORDS)