Endogenous Triglyceride and Glycogen in Perfused Rat Hearts

Mobilization of endogenous lipid and glycogen by the isolated rat heart in vitro has been studied under a variety of conditions. Recirculating perfusion of hearts with Krebs bicarbonate buffer (45 min) led to a marked depletion (66%) of cardiac glycogen, while cardiac triglyceride was decreased by 24%. There were no changes in the levels of phospholipid, diglyceride, cholesterol ester, or free fatty acid. After perfusion for 90 min, in the absence of added substrates, endogenous glycogen and triglyceride were depleted to 16% and 38%, respectively, of the levels in the unperfused controls. During this second 45-min period of perfusion, a small but significant depletion of phospholipid also occurred, indicating that this lipid class is only used for energy after marked depletion of the other endogenous energy sources.