Epitrochlearis muscle. II. Metabolic effects of contraction and catecholamines.

Effects of isometric contraction and catecholamines on glucose and glycogen metabolism in skeletal muscle were investigated with the in vitro rat epitrochlearis preparation. Mechanical performance and glycogenolysis exhibited two phases. During the initial 30 min, muscle work was 30% greater and glycogenolysis 8- to 10-fold faster than the steady-state values in the subsequent 3-4 h of contraction. Glucose uptake was increased by contraction and remained relatively constant during stimulation. Epinephrine (10(-9) to 10(-6) M) and norepinephrine (10(-7) to 10(-5) M) produced inotropic and glycogenolytic effects blocked by propranolol but not phentolamine. Chemical sympathectomy and propranolol blocked the initial glycogenolytic and inotropic effects produced by isometric contraction, suggesting that they were caused by the release of endogenous catecholamines. Net lactate production in resting muscles accounted for > 50% of total glucosyl units utilized. During contraction net lactate production accounted < 10-15% of total glycosyl flux indicating that rat fast-twitch pale muscle is capable of significant rates of aerobic glucose oxidation. Oleate and caprylate did not affect mechanical performance, glycogen, or glucose metabolism in resting or contracting muscles.