Abstract
Summary
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.
Perfusions with epinephrine (10–5 M) or dibutyryl adenosine 3′,5′-monophosphate (dibutyryl-cAMP) for 45 min produced marked decreases in the levels of cardiac glycogen and triglyceride, but under these conditions, there was no apparent utilization of phospholipid fatty acids.
The depletion of cardiac glycogen during perfusion with buffer alone (45 min) was partially prevented, and depletion of cardiac triglyceride was completely abolished when glucose (9.2 mM) or albumin-bound palmitate (0.5 mM) were added to the perfusate. Perfusion with heparin resulted in a decrease in cardiac glycogen but did not affect triglycerides. The results suggest that cardiac triglycerides provide a secondary endogenous source of energy to the heart in vitro, only after marked depletion of glycogen; phospholipid fatty acids may be utilized following exhaustion of these other endogenous energy sources.
Get full access to this article
View all access options for this article.