Utilization of Endogenous Lipids by the Isolated Perfused Rat Heart

Abstract

The isolated perfused rat heart, which beats at rates commensurate with those observed in situ, is a reasonable model for the study of metabolic changes occurring during muscular exercise. We have used this preparation to study the utilization of endogenous lipids in the absence of oxidizable substrates in the perfusing medium (9). Fisher and Williamson (6) observed that hearts perfused without exogenous substrate would continue to beat for 1–2 hours, despite the disappearance of glycogen in 15–30 minutes. We have observed a limited availability of cardiac lipids to serve as fuel for contraction, the biggest contribution being made by neutral glycerides, and that under these conditions the heart fails to maintain its initial force of contractility. Today I should like to discuss 1) the general effects of perfusion of the isolated rat heart with a substrate-free medium upon contractility and the labile phosphate stores; 2) the changes which occur in intermediary metabolites of glycolysis and in the lipids over a two hour period of perfusion; and 3) the behavior of cardiac mitochondria isolated from perfused rat hearts at various times during depletion of the available endogenous substrates.