Hemodynamics of metoprolol and pindolol in systemic hypertension with particular reference to reversal of structural vascular changes.

In a double-blind, comparative study metoprolol (100 to 300 mg/day) or pindolol (5 to 15 mg/day) was given in randomized order to 39 patients with uncomplicated essential hypertension. Peripheral hemodynamics were studied by noninvasive means after an initial 6-week placebo period and again after 6 weeks and 6 months of active treatment. Three patients withdrew from the trial during the 6-week period of active treatment. Heart rate during exercise on an ergometric bicycle to a predetermined workload indicated that the degree of beta-adrenoceptor blockade was identical during treatment with either metoprolol or pindolol. Both agents also reduced resting blood pressure to the same extent. Heart rate at rest fell considerably more during metoprolol than pindolol therapy, while vascular resistance was reduced by pindolol but not by metoprolol. This indicates that the antihypertensive effect of metoprolol can be ascribed mainly to cardiac mechanisms; in contrast, pindolol appears to lower blood pressure primarily through vascular effects. Studies at maximal dilatation showed that pindolol, but not metoprolol, reduced resistance at maximal dilatation after 6 months of treatment, indicating that a reversal of the structural vascular changes had occurred. The hemodynamic differences between the 2 agents can probably be explained by the fact that pindolol with its intrinsic sympathomimetic activity acts as a partial agonist causing active stimulation of vascular beta 2 adrenoceptors and relaxation of resistance vessels.