alpha-Methyldopa and beta-blockers in hypertension--a comparison of their haemodynamic effects.

1. During acute injection of alpha-methyldopa there is a reduction in the blood pressure within a period of a few hours and a modest reduction in the cardiac output, sometimes due to a modest decrease in heart rate. Frequently the total peripheral resistance is decreased. In contrast, acute injection of beta-blockers induces a marked decrease in heart rate and cardiac output, a compensatory increase in the total peripheral resistance and no decrease in the blood pressure. 2. During long-term use alpha-methyldopa frequently reduces the total peripheral resistance and the reduction in cardiac output is usually modest, at rest as well as during exercise. The beta-blockers reduce the blood pressure, but induce a marked decrease in cardiac output and heart rate. The total peripheral resistance is little affected compared to the pre-treatment level.