Myocardial Metabolism IV. Metabolism of Free and Esterified Cholesterol by the Perfused Rat Heart and Homogenates∗

Several aspects of the myocardial metabolism of cholesterol and its esters have been investigated using isolated perfused rat heart and heart homogenates. Between 35-50% of tracer amounts of circulating cholesterol-4-14C and cholesterol palmitate-1-14C were extracted by the heart during 45-min perfusion, but there was no indication of cholesterol ester synthesis or hydrolysis either in the medium or in the heart. Similar studies using heart homogenates revealed the lack of detectable enzymatic hydrolysis of cholesterol oleate and absence of both low- and high-energy-requiring ester synthesizing systems. Further evidence for the inability of heart tissue to split sterol esters was based on the finding that 14CO2was not produced from the palmitate-1-14C moiety of the ester. When diluted rat lymph containing 87% cholesterol-4-14C ester was perfused, about 5% of the circulating label was recovered in the myocardium, and of this, 80% was still esterified sterol.