Skeletal muscle glycolysis during submaximal exercise following acute beta-adrenergic blockade in man

Abstract

The present study describes the influence of beta-adrenergic blockade on glycogen utilization and lactate accumulation in skeletal muscle of exercising man. Twelve physically active men were examined during 25 min of continuous cycle exercise equivalent to 65% of their maximal oxygen uptake both with and without oral administration of 80 mg of propranolol (Inderal). Heart rate, oxygen uptake, rate of perceived exertion (RPE) and blood lactate concentration were measured during exercise. Muscle biopsies were obtained from m. vastus lateralis after 5 and 25 min of exercise. Beta-adrenergic blockade decreased steady state exercise heart rate by (mean +/- SD) 35 +/- 10 beats . min-1 (P less than 0.001) and oxygen uptake from 2.47 to 2.39 l . min-1 (P less than 0.01). Muscle glycogen decreased from the 5th to the 25th min of exercise, and beta-blockade had no significant effect on this decrease. In contrast to without drug, beta-blockade resulted in a decrease (P less than 0.05) in muscle lactate concentration from the 5th (6.9 mmol . kg-1 w./w.) to the 25th min (4.8 mmol . kg-1 w./w.). Similarly blood lactate levels were lower (P less than 0.05) with than without beta-blockade in the last but not the first 10 min of exercise. The alteration in muscle lactate concentration pattern following beta-blockade, may imply that adrenergic effects per se contribute to the stimulation of glycolysis during submaximal exercise, except in its earliest phase. Nevertheless, the effect is not great enough to produce substantial differences in glycogen utilization.