LACK OF EFFECT OF PROPRANOLOL ON CANINE CORONARY COLLATERAL DEVELOPMENT DURING PROGRESSIVE CORONARY STENOSIS AND OCCLUSION

Objective: The aim was to test the effect of propranolol, a beta adrenergic receptor blocking drug which diminishes myocardial ischaemia, on coronary collateral development. Methods: Dogs were chronically instrumented with a left circumflex coronary artery Doppler flow probe, ameroid constrictor, pneumatic occluder, and left atrial and aortic catheters. Haemodynamic studies and measurements of normal myocardial and collateral blood flows were performed at least weekly after surgery, or sooner if the left circumflex artery occluded spontaneously, in eight control dogs and seven animals treated with propranolol, 240 mg twice daily (a dose which successfully attenuated the chronotropic effect of a graded infusion of isoprenaline). In dogs in which the left circumflex artery occluded within the first four weeks after surgery, collateral blood flow was measured during exercise on a motorised treadmill. Results: There was no difference between the groups in the rate or pattern of coronary collateral development, magnitude of collateral flow before or after spontaneous left circumflex occlusion, and collateral vascular reserve during exercise. At the time of coronary occlusion resting collateral flow was equivalent to normal perfusion levels in both groups and averaged 87-96% of normal flows during exercise. Conclusions: Propranolol has no observable effect on coronary collateral development despite its acknowledged ability to prevent or attenuate myocardial ischaemia.