Initial cholesterol esterification rate in hyperlipoproteinaemia: effects of triglyceride-rich lipoproteins.

The initial cholesterol esterification rate (LCAT activity) was determined in ninety-four hyperlipidaemic subjects. LCAT activity was elevated in hypertriglyceridaemia, whereas patients with hypercholesterolaemia had normal activities. In hypertriglyceridaemic subjects LCAT activity correlated with the concentrations of d less than 1.006 lipoproteins, plasma triglycerides, cholesterol and cholesterol esters and phospholipid levels. Addition of d less than 1.006 lipoprotein to normal plasma resulted in a dose dependent stimulation of enzyme activity with a sigmoidal response curve. When the d less than 1.006 lipoproteins were removed from hypertriglyceridaemic plasma by ultracentrifugation, the enzyme activity in the residual d greater than 1.006 fraction dropped, but still was higher than in normal plasma and correlated with the amount of d less than 1.006 lipoproteins originally present. Thus, high LCAT activity in hypertriglyceridaemia cannot be explained solely by the presence of an increased d less than 1.006 lipoprotein concentration. An increase of enzyme concentration or changes in concentration or composition of other lipoproteins (high density lipoproteins) may contribute to the high LCAT activity in hypertriglyceridaemia.