The role of beta adrenoceptors in the coronary and systemic hemodynamic responses to emotional stress in conscious dogs

The present observations were made to investigate the role of beta adrenoceptors in the hemodynamic response to stress in conscious dogs. Probes for electromagnetic flowmeter were implanted on the ascending aorta and left circumflex coronary artery and a catheter was inserted into the aortic arch, 15 days before observations were made. Emotional stress, produced by firing a gun, increased heart rate, cardiac output, and left ventricular work. The responses were reduced by propranolol, practolol, and sotalol, 0.2 and 1.0 mg. per kilogram of body weight, and abolished by alprenolol. The difference between the effect of alprenolol and the other drugs may result from the marked intrinsic sympathomimetic activity of alprenolol which increased the resting levels of heart rate, cardiac output, and left ventricular work. Emotional stress increased mean blood flow through the left circumflex coronary artery as aresult of increase in stroke coronary flow and heart rate. Propranolol, sotalol, and practolol reduced the increase in mean coronary flow produced by stress through a reduction in tachycardia; the increase in stroke coronary flow was unaltered. The decreases in mean and late diastolic coronary resistance produced by stress were not altered by these three drugs. Alprenolol, unlike the other drugs, completely abolished the increases in mean and stroke circumflex coronary flow and the decreases in coronary vascular resistance produced by stress. The present observations indicate that the dilatation of coronary arteries produced by stress does not result entirely from an increase in cardiac metabolism; they also suggest that stimulation of beta adrenoceptors in the coronary arteries plays an important role in the coronary vasodilation produced by emotional stress.