Utilization of endogenous lipid by the isolated perfused rat heart

Abstract

The lipids of the rat heart were studied with regard to amount, classes present and fatty acid composition of free fatty acids, trigly-cerides and phospholipids. Myocardial lipid contained 300 [mu] moles of total fatty acid/g dry wt. of which only 2-4 umoles were free; the remainder was esterified, chiefly as phospholipid. Neutral esters, of which triglyceride was the principal form, made up 15 percent of the total fatty acids. When normal hearts were perfused with a nutrient-free medium until exhaustion, the triglyceride concentration declined from 43 to 13 [mu]moles/g. dry wt. The content of phospholipids, partial gly-cerides and cholesteryl esters did not change. When the lipids of the rat heart were labelled with [leucine-C14] palmitate before perfusion with non-nutrient medium, radioactivity disappeared from the triglyceride, diglyceride and free fatty acid fractions, but not from the phospholipid or other ester classes. These experiments support the view that only a small fraction of the total cardiac lipid, principally trigly-cerides and to a smaller extent diglycerides, is available as a source of fuel in the absence of exogenous substrate.