Influence of beta-blockade with beta-1-selectivity or intrinsic sympathomimetic activity on some cardiorespiratory responses to exercise
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Possession of beta-1-selectivity and intrinsic sympathomimetic activity (ISA) by beta-adrenergic blocking drugs have been found to modify the effects of these drugs on heart rate, blood pressure and pulmonary airway resistance both at rest and during exercise. In a randomised, double-blind, cross-over, placebo-controlled trial, 21 healthy male volunteers took placebo, propranolol (non-selective with no ISA), metoprolol (beta-1-selective with no ISA) and pindolol (non-selective with ISA) on separate occasions prior to an exercise test using the same protocol each time. Heart rate, blood pressure and peak respiratory flow rate (PEFR) were measured before exercise and at exhaustion. No significant differences in percentage increase in heart rate after exercise were detected between placebo and all the three beta-blockers. All three drugs were associated with significantly lower percentage increases in systolic blood pressure with exercise compared to placebo; with metoprolol and propranolol causing lower increases than pindolol. The index of myocardial oxygen consumption, MVO2, was highest with pindolol. PEFR was reduced most by propranolol. Possession of beta-1-selectivity and ISA by beta-blocking drugs modifies their effects on cardio-respiratory responses to exercise amongst indigenous Kenyans.