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[Oxidative energy metabolism and cardiac contractility in rat heart during graded reductions of coronary flow].

The relationships between cardiac contractility, myocardial oxygenation and high energy phosphates content were evaluated during graded reduction of coronary flow in the isolated rat heart. Myocardial oxygenation and high energy phosphates content were measured by optical and 31P-NMR methods, respectively. The rate-pressure product decreased along with flow rate reduction. Phosphocreatine to inorganic phosphate ratio (PCr/Pi) was unchanged until the coronary flow was reduced to 2 ml/min and started to decrease below 2 ml/min. No significant change in ATP was noted until the coronary flow was reduced to 0.5 ml/min. The oxygenation state of myoglobin and cytochrome-aa3 remained at aerobic level until the flow rate was decreased to 2 ml/min. When the coronary flow rate was reduced below 2 ml/min, cytochrome-aa3 was reduced in parallel with the deoxygenation of myoglobin. These results suggest that the mechanism of decreased contractility modulated by reduction of coronary flow is independent of oxidative energy production. We conclude that this mechanism is not caused by the reduced oxygen delivery to tissue, but that the heart senses either the reduction of coronary flow or pressure.