Effect of adrenergic activation on collateral coronary blood flow.

Myocardial tissue blood flow of the left ventricle was measured by means of the heat clearance technique in open chest dogs under chloralose. The myocardial segment chosen for the flow measurement was rendered ischemic by occlusion of the left anterior descending (LAD) artery. In the ischemic state the area explored was supplied exclusively by the collateral vessels. Local vascular responses to various forms of adrenergic excitation (stellate stimulation, administration of noradrenaline and isoproterenol) were registered both before and after coronary occlusion. Coronary reactions were expressed as per cent local vascular conductance changes. In the normal state all forms of the adrenergic activation elicited significant coronary dilatation (increase in vascular conductance). After coronary occlusion the average value of this coronary dilatation considerably decreased. At the same time, a systematic inverse relationship was found between the resting level of the collateral vascular conductance and its chance for an increase during adrenergic activation; in cases of high resting collateral conductance values, instead of an increase, a decrease was observed during stellate stimulation and noradrenaline administration. Pure beta-adrenergic activation induced by isoproterenol did not elicit similar decreases in the collateral conductance. The results suggest that adrenergic activation is able to upset an uncertain intrinsic vascular balance in the ischemic myocardium.