Hemodynamic and metabolic effects of beta-adrenergic blockade in exercising dogs.

Abstract

Twelve dogs were trained to run on the motor-driven treadmill at speeds of 3-9 km/hr. up a 5% Incline. After training, chronic indwelling catheters were placed in the aorta and pulmonary artery. Each animal was studied at rest and after 8 min. of exercise at 3, 6 and 9 km/ hr. and the studies repeated after beta-adrenerglc blockade had been induced by Intravenous administration of 0.25 mg/kg propranolol. Beta-adrenergic blockade caused no significant alteration in mean aortic or pulmonary artery pressure at any exercise level but rise in heart rate and increase in cardiac output (measured by the dye-dilution technique) were significantly less at the highest exercise level. By sampling arterial and mixed venous blood It was shown that the reduction In cardiac output following adrenergic blockade was almost entirely compensated for by a widening of the arteriovenous Oj difference. Beta-adrenergic blockade had no effect on the response of arterial pH and PCO2 to graded exercise. The rise in arterial free fatty acid and lactate concentrations and in the lactate pyruvate ratio, which occurs normally in dogs during exercise of this length and severity, was completely abolished by beta-adrenergic blockade.