EFFECTS OF VARIOUS CORONARY VASODILATORS ON MYOCARDIAL OXYGEN CONSUMPTION

Abstract

Effects of various coronary vasodilators were compared with those of isoprenaline in modified Langendorff's dog heart preparation with cross-circulation by a donor dog. Coronary vasodilators used in this study all induced a significant increase in the rate of coronary blood flow with a decrease in the A-V O₂ difference. The coronary vasodilating activity was in the following order; nifedipine>nitroglycerin >iproveratril>dipyridamole, prenylamine, lidoflazine, papaverine>carbochromene, trapymin>visnadin, khellin, which was to 1: 1/3: 1/10: 1/100: 1/300: 1/1000. These compounds caused a greater increase in the rate of coronary blood flow rather than changes in myocardial oxygen consumption but in a different grade, while isoprenaline caused a vasodilation paralleling an increase in myocardial oxygen consumption. Thus, the ratios of coronary blood flow v.s. myocardial oxygen consumption were approx. graded as follows; nitroglycerin, iproveratril, dipyridamole>nifedipine, lidoflazine, prenylamine, carbochromene, papaverine, visnadin>trapymin, khellin. It is concluded that the vascular smooth muscle of the coronary artery is mainly relaxed by the direct action of these drugs but partly by the indirect metabolic effect on the cardiac muscle. Different mechanisms of relaxation of the coronary artery lead to classification of coronary vasodilators into several different groups.