RESISTANCE OF CONTRACTING MYOCARDIUM TO SWELLING WITH HYPOXIA AND GLYCOLYTIC BLOCKADE

Summary: The interrelationship of myocardial metabolism, performance and tissue hydration was examined in isolated contracting rat, Guinea pig and dog myocardium. Myocardial metabolism was altered by blocking aerobic, and both aerobic and anaerobic metabolism. Myocardial water content and distribution were measured in rat myocardium using 3H-inulin and 51Cr-EDTA as extracellular markers. Myocardial hydration was also evaluated by light and electron microscopy. The relative susceptibility of non-contracting slices of rat and Guinea pig myocardium and kidney to swelling secondary to these interventions was also explored. Hypoxia resulted in a partially reversible reduc- tion in mechanical function; hypoxia plus glycolytic blockade led to irreversible severe contracture and total loss of tension development. Neither hypoxia nor hypoxia plus glycolytic blockade resulted in increased total tissue or extracellular water in previously contracting preparations or in non-contracting slices of myocardium. On the other hand, there were significant increases in cellular water in similarly treated kidney slices after each intervention. Thus, despite severe, irreversible derangements of mechanical function, myocardium did not swell under conditions which produced swelling in renal cortex.