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

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 pO(2). 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 beta-blockade, did not support the suggestion that the reduction in coronary flow after beta-blockade was due to the unmasking of an active vasoconstriction.