Effect of beta-adrenergic blockade on biochemical and metabolic response to exercise.
During normal exercise the myocardium, skeletal muscle, liver and adipose tissue all participate in the metabolic response to exercise. Beta-blockade, by impairing this biochemical-metabolic response at several levels, limits the capacity for maximal exercise. The relevant effects of beta blockade may include hypoglycemia, impaired mobilization of free fatty acids and decreased breakdown of glycogen in skeletal muscle. The organs responsible for these metabolic changes are the liver (blood sugar), adipose tissue (blood free fatty acids) and skeletal muscle. Most of the metabolic beta-adrenergic receptors are thought to be beta 2 in nature. Two populations of receptors (mixed beta 1 and beta 2) may explain some controversial findings. Overall, the data suggest that cardioselective agents may have less effect than nonselective agents in producing metabolic impairment during sustained exercise.