Abstract

A reproducible method has been devised for depressing the force of contraction of isolated perfused rat hearts with halothane. Approximately 6 mg/100 ml of halothane in the perfusate were required to maintaiui 50% depression over a 2-hr period. To achieve 98% depression, 17 mg/100 ml were required. Recovery of force of contraction was virtually complete on stopping the administration of halothane. Neither concentration of halothane resulted in a significant change in perfusion rate, but the latter concentration produced a decrease in tissue potassium content. Anoxia (i.e., 95% N₂-5% CO₂ imistead of 95% 0₂-5% CO₂) produced a 90% decrease in force of contraction, which was maintained over a 2-hr period. Recovery of force of contraction upon admission of oxygen was slower and less complete than recovery from halothane. In addition, anoxia produced an increase in perfusion rate and a decrease in tissue potassium content. Despite the fact that anoxia and halothane produced similar changes in force of contraction and potassium content, the differences in perfusion rate and recovery of force of contraction indicate that different biochemical changes are occurring in the cells.