Effects of Persantin and Nitroglycerin on Myocardial Blood Flow During Temporary Coronary Occlusions in Dogs

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Abstract
The Kr85 clearance technique was used to study the effects of Persantin and nitroglycerin on myocardial blood flow during temporary coronary occlusions in dogs. The 2 vasodilator drugs were administered either close-arterially or intravenously, and their effects were then followed by flow measurements during 2-4 periods of coronary occlusion in the subsequent 1/2-1 hr. Persantin (0.25-1.0 mg/kg close-arterially, or 0.25-1.5 mg/kg intravenously) produced maximal, or nearly maximal, dilatation of the coronary vasculature surrounding the ischemic muscle region, and this drug also increased the collateral blood supply by some 25-30%, despite a 10-20% fall in arterial blood pressure. The experimental analysis of this effect indicates that Persantin induces a true dilatation of those secretions of the collateral arterial connections that are placed outside the ischemic area, thus improving its blood supply. On the other hand, the vessels placed within the ischemic region are already maximally dilated, evidently as the result of ischemia. Also, Persantin seems to improve the collateral blood supply to the ischemic area in an indrect, extravascular manner, by reducing left ventricular volume and end-diastolic pressure. This tends to improve the effective perfusion pressure for the ischemic region, to increase the transmural pressure within its vessel and to decrease their length. Close-arterial or intravenous administration of nitroglycerin (0.02-0.3 mg/kg) produced also a true dilatation of the unrestricted coronary vascular bed, as reflected by an almost unchanged blood flow despite the often profound drop in systemic pressure. The latter fell, however, more than the collateral blood supply which decreased some 15-20% following nitroglycerin. Thus, the dilator action of nitroglycerin on the collateral vessels was usually more than outweighed by the drug-induced fall in systemic blood pressure. The effects of either drug was sustained for at least 30 minutes, but neither drug was capable of reducing the relative size of the ischemic muscle area. Some clinical implications made by the divergent drug actions are discussed.