METABOLIC AND HORMONAL RESPONSE TO PHYSICAL EXERCISE UNDER ACUTE BETA-1-ADRENERGIC BLOCKADE

  • 1 January 1981
    • journal article
    • research article
    • Vol. 70  (5) , 406-412
Abstract
In 14 healthy physical education students the effect of acute .beta.1-adrenergic blockade (100 mg metoprolol) on maximal and prolonged exercise capacity, carbohydrate and lipid metabolism, catecholamines, insulin, growth hormone and cortisol was studied in a double-blind trial. Metoprolol had no effect on maximal O2 uptake. The 3.5% reduction of maximal exercise capacity was attributed to the reduced maximal lactate concentration. Maximal heart rate was reduced by .apprx. 22%. At submaximal work loads (treadmill exercise with gradually increasing velocity), lipolysis appeared to be inhibited; arterial glucose and lactate concentrations were unaffected. With metoprolol, epinephrine levels at rest and submaximal work loads were elevated; no effect was apparent at maximal loads. Norepinephrine, insulin, growth hormone and cortisol were unaffected in exercise with increasing work loads. In prolonged exercise at a constant load of .apprx. 70% of maximal exercise capacity, mean heart rate was reduced by 26%. Arterial lactate and glucose levels were essentially unchanged, and free fatty acids and glycerol decreased by 50 and 30%, respectively. With metoprolol, epinephrine increased by 100%, norepinephrine by 50%, growth hormone by 60% and cortisol by 90%; insulin remained unchanged. A reduction of exercise capacity by .beta.1-adrenergic blockade in patients undergoing an endurance type training for therapeutic or rehabilitative purposes is unlikely to occur. The inhibition of lipolysis under metoprolol appears to be counteracted by the increased carbohydrate utilization and by the increased secretion of the regulating hormones.