Changes in in vitro myocardial hydration and performance in response to transient metabolic blockade in hypertonic, isotonic, and hypotonic media

Abstract

The effect of changes in tonicity of the bathing media on in vitro myocardial H2O content and mechanical performance during hypoxia and total metabolic blockade (consisting of hypoxia plus glycolytic blockade) was studied in 175 isometrically contracting rat papillary muscles. Recovery of mechanical performance after metabolic blockade in hypertonic (440 mOsm [milliosmolar]), isotonic (315 mOsm), and hypotonic (190 mOsm) media was evaluated. Myocardial H2O contents were 3.2 .+-. 0.1 cm3/g dry wt in hypertonic, 3.9 .+-. 0.1 cm3/g in isotonic and 4.5 .+-. 0.1 cm3/g in hypotonic media. Addition of metabolic blockade did not alter myocardial H2O content. Return to isotonic solution resulted in restoration of normal myocardial H2O content with and without continued metabolic blockade. Developed tension fell during hypoxia in all 3 media, and recovered partially with reoxygenation and return to isotonic solution. Recovery was best after hypoxia in an isotonic medium and poorest after hypoxia in a hypertonic medium. Tension development was completely lost after less than 15 min of total metabolic blockade and remained absent after removal of glycolytic blockade and reoxygenation regardless of the tonicity of the bathing solution. Appropriate fluid shifts between myocardium and bathing solution in response to alterations in the tonicity of the bath were observed despite total irreversible loss of tension development. The concept that hypertonic solutions protect the myocardium during metabolic blockade was not supported.