Effect of substrate supply and beta-adrenergic blockade on heart glycogen and triglyceride utilization during exercise in the rat.

Exercise-induced heart glycogen and triglyceride mobilization was studied in control rats, in rats with reduced blood glycose supply (fasted rats), in rats with reduced plasma free fatty acids (FFA) supply (nicotinic acid-treated rats), and in rats with blockade of beta-adrenergic receptors (propranolol-treated rats). It was found in the fed control rats that both the heart glycogen and triglyceride levels were reduced at the beginning of the exercise and thereafter they returned to the control level despite the exercise being continued. The triglyceride level was reduced again during the exhaustive exercise. Reduced blood glucose supply increased the heart glycogen and triglyceride utilization during exercise. Partial prevention of the plasma FFA elevation during exercise increased the heart glycogen utilization and had no effect on utilization of the heart triglycerides. Blockade of the beta-adrenergic receptors fully prevented both the heart glycogen and triglyceride mobilization during exercise.