Time-dependent changes of collateral coronary reactivity in the dog.

Vascular reactivity of the developing coronary collaterals has been investigated by studying local flow responses elicited by adrenergic and hypoxic stimuli in the ischemic foci of the canine heart. Tissue blood flow was measured by means of the heat clearance technique. The myocardial area explored was rendered ischemic by ligating the left anterior descending coronary artery 2-90 days prior to the experiment. This area is supplied exclusively by collateral channels. Adrenergic sensitivity was tested by i.v. administration or noradrenaline and isoproterenol (1 mug/kh), as well as by supramaximal electrical stimulation of the stellate ganglion. Metabolic sensitivity of the vessels was tested by brief periods of general hypoxia. During the first 3 weeks of the myocardial infarction, the collateral vascular response induced by each form of the adrenergic activation was considerably different from that observed in the normal coronary bed: instead of the conventional beta-type dilation, noradrenaline and stellate stimulation induced constriction in the ischemic zone whereas isoproterenol, having only pure beta-stimulating effects proved to be ineffective. Following the 3rd postoperative week, a gradually increasing sensitivity to beta-dilator influences appeared on the collateral vessels. However, this transformation of the adrenergic effect was not accompanied by a similar restoration of the local vascular propensity for metabolic (hypoxic) dilation. The results suggest that time courses of the changes of the adrenergic and metabolic vascular reactivity in the collateral network, although probably interrelated, do not parallel each other.