Effect of acetylstrophanthidin on myocardial function and K+ and Ca2+ exchange in newborn rabbit

Abstract

The effects of acetylstrophanthidin (AS) on the mechanical function, tissue K content and tissue Ca content were studied in the isolated, arterially perfused newborn and adult rabbit septum. Newborn and adult muscles were perfused with Krebs-Henseleit solutions containing 0.25, 0.5, 1.0, 1.5, 2.5 or 5.0 .times. 10-6 M AS. 42K and 47Ca were used in the measurement of tissue uptakes of these ions. The inotropic effect of AS in the newborn was equal to that in the adult for AS concentrations less than 1.0 .times. 10-6 M but was greater (P < 0.01) than that in the adult at higher concentrations. In muscles perfused with solutions containing AS concentrations higher than 0.5 .times. 10-6 M in the adult and 1 .times. 10-6 M in the newborn, contractility increased initially and then decreased (mechanical toxicity). Mechanical toxicity in the adult occurred sooner than in the newborn. A decrease in tissue K and an increase in tissue Ca were observed immediately after AS infusion in the 2 age groups. The rates of tissue K loss and Ca gain in the newborn were not significantly different from those in the adult. Mechanical toxicity in the newborn was less than that in the adult for an equal amount of tissue K loss and/or tissue Ca gain. In the isolated arterially perfused septal preparation, the newborn myocardium tolerates larger concentrations of AS, resulting in a greater inotropic effect which is observed before the onset of toxicity.