Effect of brief myocardial ischemia on sympathetic coronary vasoconstriction

The purpose of the present study was to determine whether sympathetic coronary vasoconstrictor responses are altered after brief ischemia and reperfusion. Adult mongrel dogs were anesthetized and instrumented for measurements of heart rate, arterial pressure, left ventricular pressure, left ventricular dP/dt, anterior myocardial wall thickening, and left circumflex coronary artery (LCX) and left anterior descending coronary artery (LAD) blood flow velocities. Changes in coronary vascular resistance were recorded during intravenous bolus doses of norepinephrine and bilateral electrical stimulation of the stellate ganglia. After f3-adrenergic blockade and bilateral vagotomy, electrical stimulation of the stellate ganglia increased coronary vascular resistance in the LAD and LCX beds by 38±5 % and 39±5%, respectively. After a 15-minute LAD occlusion, repeat electrical stimulation produced increases in coronary resistance of 16±3 % and 45±8%, respectively (p<0.05 for the LAD before versus after the occlusion). The peak increase in coronary vascular resistance to two doses of norepinephrine was unchanged. After a shorter period of myocardial ischemia (7 minutes), similar increases in coronary resistance to stellate stimulation were observed before (27±4%) and after (26±6%) myocardial ischemia. The mechanism of this impaired sympathetic coronary vasoconstriction was further tested by examining the responses to bretylium and tyramine. Brief ischemia did not alter the coronary constrictor response