The effect of beta-adrenergic blockade on leg blood flow with repeated maximal contractions of the triceps surae muscle group in man

Summary

The effect of β-adrenergic blockade on torque output and leg blood flow was examined in seven healthy young men during repeated maximal isometric voluntary contractions of the triceps surae muscle group. Exercise was performed in either a bent- or straight-leg position during each of four drug treatments: placebo, propranolol, metoprolol, oxprenolol. Contractions were sustained for 5 s with 5 s relaxation for a total of 10 min followed by a 10-min recovery. Leg blood flow was measured during the 5 s relaxation separating contractions using strain gauge plethysmography. Torque output decreased during the 10-min contractions with no differences between the four drug treatments. Leg blood flow was lower with β-blockade during the initial stages of exercise and recovery in the bent-leg position but no differences were observed after 3 min exercise or recovery. Leg blood flow in the straight-leg position was not different between any of the four drug treatments, but it was significantly less than in bent-leg exercise. The lower blood flows during the initial stages of exercise in the β-blocked conditions probably reflect a slowing of the central cardiovascular response because of β₁-receptor blockade of the heart rather than on the β₂-receptors effects on peripheral vacular resistance. It is concluded that local vasodilator substances released from the working muscle may play a more important role than β₂-receptor stimulation of smooth muscle in skeletal muscle resistance vessels in regulating local muscle blood flow during maximal exercise of the triceps surae muscle group.