Turnover of plasma cholesteryl esters and its relationship to other parameters of lipid metabolism in man.

Studies on plasma cholesteryl esters were made in 32 normal and hyperlipidaemic subjects in an attempt to elucidate further the metabolic relationships between cholesterol and other plasma lipids and lipoproteins. Fractional and net turnover rates of plasma cholesteryl esters were measured using two independent (in vivo and in vitro) methods, both of which determined the prevailing activity of plasma lecithin: cholesterol acyltransferase in the ambiance of the patients own plasma. The results obtained by the two methods were in excellent agreement. The turnover rates of plasma cholesteryl esters in hypertriglyceridaemic patients were significantly greater than in patients with only hypercholesterolaemia and in those with normal plasma lipids. In agreement with these observations, the esterified to free cholesterol ratios in hypertriglyceridaemic patients were significantly greater than in those with normal plasma triglycerides. Patients who had only hypercholesterolaemia had normal esterified to free cholesterol ratios. The rates of esterification of plasma free cholesterol correlated well with triglyceride concentrations as well as with the net turnover of plasma triglycerides and also with the turnover or synthesis of endogenous cholesterol. Since the turnover of plasma triglycerides in most patients with modest to moderate hypertriglyceridaemia reflects the turnover of their plasma very low density lipoproteins, it is suggested that it is the turnover of these lipoproteins which correlates with the hepatic synthesis of cholesterol and with the esterification of plasma cholesteryl esters.