Mechanisms mediating the coronary vascular response to behavioral stress in the dog.

Left circumflex coronary blood flow (CBF) was measured in eight mongrel dogs with 8 MHz continuous wave Doppler flow transducers during classical aversive conditioning. The cardiovascular condition response consisted of significant (P less than 0.01) increases in: (1) mean aortic pressure (16.1%), (2) d(left ventricular pressure)/dt (64.2%), and (3) heart rate (63.2%). The coronary vascular response to behavioral stress consisted of an initial late diastolic decrease in CBF (12.5%) between 5 and 10 seconds after conditional stimulus onset, followed by a significant increase in CBF (96.8%). Concurrently, late diastolic coronary vascular resistance (CVR) first significantly increased (21.9%), then significantly decreased (39.8%). The increase in CVR was attenuated by cardiac pacing and converted into a significant decrease after alpha-receptor blockade. The decrease in CVR was reduced either by cardiac pacing or cardioselective beta-receptor blockage and eliminated by the combination of alpha- and beta-receptor blockade. Thus, these data indicate that the coronary vascular response to stress consisted of two components: an initial alpha-adrenergic coronary vasoconstriction, followed by a more complex vasodilation which was probably mediated by metabolites released secondarily to increases in heart rate and inotropic state.