Effect of Physical Training on the Mechanical and Metabolic Response of the Rat Heart to Hypoxia

Abstract

To study the effects of physical conditioning on cardiac function and metabolism during hypoxia, rats were conditioned by swimming. Their isolated hearts and hearts of sedentary rats were studied under isovolumic conditions and also while performing external work. During isovolumic performance only minimal improvement in hypoxic cardiac performance was observed because of conditioning. While performing external work during hypoxia cardiac output and cardiac work were approximately twice as great in hearts from conditioned rats as in those from sedentary rats. There were also slightly higher peak systolic pressures and mean left ventricular systolic pressures during hypoxia. Oxygen delivery and lactate production during hypoxia were the same in hearts from conditioned and sedentary rats as were myocardial NADH fluorescence, residual high-energy phosphate stores, and myocardial glycogen levels. External efficiency in experiments on working rat hearts was twice as great during hypoxia in hearts from conditioned rats as in those fromsedentary rats. The data suggest that hearts of conditioned rats have enhanced pumping capacity when subjected to hypoxia compared with hearts of sedentary rats. Oxygen delivery and energy formation during hypoxia are not improved in hearts of conditioned animals. The major reason for improved performance appears to be more efficient energy utilization for external cardiac work.