EFFECT OF NITROGLYCERIN AND DIPYRIDAMOLE ON EPICARDIAL AND ENDOCARDIAL OXYGEN TENSION—FURTHER EVIDENCE FOR REDISTRIBUTION OF MYOCARDIAL BLOOD FLOW

¹ Department of Pharmacology, Warner-Lambert Research Institute, Morris Plains, New Jersey

Intramyocardial oxygen tension was determined in the subepicardial and subendocardial regions of the left ventricle of dogs by a polarographic technique. Animals were respired with room air. Subepicardial and subendocardial oxygen tension averaged 25.7 and 16.5 mm Hg, respectively. Nitroglycerin, 5 to 20 µg/kg i.v., produced an initial decline in aortic pressure, coronary flow and endocardial and epicardial oxygen tension, but as blood flow and aortic pressure returned toward normal, endocardial oxygen tension increased about 7 mm Hg above control levels and remained elevated for 12 to 15 minutes. Epicardial oxygen tension merely returned to control levels. Intracoronary injection of 2 to 4 µg of nitroglycerin also produced a selective increase in endocardal oxygen tension. Dipyridamole, i.v., produced a prolonged increase of coronary blood flow with little consistent effect on oxygen tension. Coronary occlusion caused a rapid fall in endocardial oxygen tension, but changes in the epicardium were more variable. The selective increase in endocardial oxygen tension produced by nitroglycerin may be a result of redistribution of blood flow from epicardium to endocardium and/or a decrease in cardiac work and metabolism.