NUTRITIONAL CIRCULATION IN THE HEART. III. EFFECT OF ISOPROTERENOL AND BETA ADENERGIC BLOCKADE ON MYOCARDIAL HEMODYNAMICS AND RUBIDIUM-86 EXTRACTION IN THE ISOLATED SUPPORTED HEART PREPARATION

¹ Department of Pharmacology, Marquette School of Medicine, Milwaukee, Wisconsin

In the isolated supported heart preparation, an intracoronary infusion of 0.05 or 0.1 µg/min of isoproterenol produced a significant increase in heart rate, left ventricular contractile force, left ventricular peak systolic pressure and myocardial oxygen consumption and a decrease in the coronary artery perfusion pressure. Isoproterenol also decreased the extraction of rubidium-86 (ERb⁸⁶) by the heart and the calculated values for Rb⁸⁶ clearance (CRb⁸⁶) and the capillary transport coefficient (PS). A mechanical increase in left ventricular systolic pressure also decreased ERb⁸⁶, CRb⁸⁶ and PS. The effects of isoproterenol upon myocardial hemodynamics, oxygen consumption and Rb⁸⁶ uptake were reduced significantly by pretreatment with 02 mg/kg of dl-propranolol or 0.25 mg/kg of ICI 50,172 but not by d-propranolol in doses up to 2 mg/kg. It is proposed that a reduction in ERb⁸⁶, CRb⁸⁶ and PS during isoproterenol infusion is indicative of a decrease in nutritional circulation (effective capillary flow). Such a decrease in nutritional blood flow may be an important factor in aggravating the ratio of oxygen demand to oxygen supply when the total coronary blood flow is fixed, and therefore may also be involved in the mechanism of precipitation of angina pectoris in patients with arteriosclerotic coronary artery lesions. it is possible that the clinical effectiveness of beta adrenergic blocking agents in the treatment of angina pectoris may be due not only to blockade of the deleterious cardiac stimulant effects of adrenergic amines, but also to an antagonism of the reduction in nutritional circulation by catecholamines.