The effects of pronethalol and propranolol on the coronary circulation of the dog

Abstract

1 . The actions of pronethalol and propranolol have been studied to see if there was any relationship between the reduction in coronary flow and any other cardiovascular action they have. 2 . The experiments were carried out in anaesthetized open chest dogs. Measurements included central arterial, left and right venous or atrial pressures, heart rate, ventricular size and stroke volume, intra-ventricular pressures, total left coronary flow, arterial and coronary sinus blood pO₂. The pressure-time index (PTI) and maximum rate of isovolumetric contraction (dp/dt) were obtained from these records. 3 . It was concluded that, in these experiments, the reduction in coronary flow produced by pronethalol and propranolol was not directly related to a decrease in perfusion pressure, a raised venous pressure, the increase in ventricular volume and hence wall tension, the decrease in heart rate, or to the increased duration of systole. 4 . The PTI and dp/dt were always reduced at the same time as the coronary flow. These findings are discussed. 5 . Studies of the effects of sympathetic stimulation, of phentolamine, of reduced arterial oxygen tension and electrical pacing of the heart, all after β-blockade, did not support the suggestion that the reduction in coronary flow after β-blockade was due to the unmasking of an active vasoconstriction.