Acute coronary occlusion: prolonged increase in collateral flow following brief administration of nitroglycerin and methoxamine.

Regional coronary blood flow was determined with the radioactive microsphere technique 10 an 70 minutes and 2 1/2 and 5 hours after abrupt occlusion of the left anterior descending coronary artery in 12 closed chest sedated dogs. In six dogs, nitroglycerin, 200 to 400 microng/min, was infused intravenously 10 to 70 minutes after occlusion. Methoxamine was administered to return blood pressure and heart rate to prenitroglycerin levels. Ten minutes after occlusion (before treatment) collateral flow values and ischemic zone endocardial/epicardial flow ratios were equivalent in untreated (0.11+/-0.03 ml/min per g; 0.31+/-0.05) and treated dogs (0.14+/-0.02 ml/min per g; 0.29+/-0.03). In untreated dogs, collateral flow did not change over 5 hours; the endocardial/epicardial flow ratio was decreased at 5 hours (0.21+/-0.05, P less than 0.05). In contrast, in treated dogs, collateral flow and the endocardial/epicardial flow ratio were increased at 70 minutes (0.27+/-0.04 ml/min per g, P less than 0.05; 0.53+/-0.10, P less than 0.05). Most importantly, collateral flow remained elevated 5 hours after occlusion (0.26+/-0.03 ml/min per g, P less than 0.05) although treatment was discontinued 70 minutes after occlusion. Hence, collateral flow was unchanged over 5 hours of occlusion in untreated dogs, but short-term treatment with nitroglycerin and methoxamine resulted in a sustained increase in collateral flow. These findings may be a result of stimulation by nitroglycerin and methoxamine of the spontaneous rate at which intrinsic collateral function increases after ischemia. Alternatively, nitroglycerin and methoxamine may maintain cell viability until collateral vessels develop spontaneously.