Effect of acidosis on skeletal muscle metabolism with and without propranolol

Abstract

Does the stimulatory effect of circulating catecholamines counteract the inhibitory effect of acidosis on skeletal muscle metabolism? To investigate this possibility, we studied gastrocnemii in dogs breathing either air (n = 10) or 4% carbon dioxide in air (n = 10) at rest and during contractions. In five dogs from each group, we infused propranolol into the arterial supply of the right and left muscles for 40 min. After 30 min of infusion, the left muscle was stimulated at 3 Hz for 10 min. During the 10th min of contractions, we removed and froze both muscles in liquid nitrogen. Oxygen uptake and blood flow to the left muscle prior to or during stimulation was not affected by acidosis either with or without propranolol. Glycogen concentration in resting muscle was unaffected by acidosis with or without propranolol. There was an acidosis related decrease of approximately 50% in the glycolytic intermediates (glucose 6-phosphate, fructose 1,6-diphosphate, α-glycerol phosphate, and dihydroxyacetone phosphate) in unstimulated muscles without β-blockade. At rest, acidosis decreased muscle lactate by 50% with and 64% without propranolol, but lactate release was decreased only with acidosis without propranolol (1.4–0.1 μmol/kg∙s). Acidosis without propranolol had no effect on the changes in glycogen concentration or the change in the concentration of glycolytic intermediates resulting from contractions. In β-blocked muscle, the difference between stimulated and unstimulated concentrations of glycogen and glycolytic intermediates including lactate was 20–50% smaller with acidosis. Thus, with β-blockade, the acidotic effects at rest disappeared and an inhibition of the metabolic adjustment to contractions appeared, indicating that circulating catecholamines do modify some metabolic effects of acidosis.Key words: oxidative muscle, glycogen, lactate efflux, glycolytic intermediates, β-blockade.