In Vitro Determination of Lecithin: Cholesterol Acyltransferase in Plasma

Abstract

Determination of the initial rate of lecithin: cholesterol acyltransferase (LCAT) activity has been performed by the method of Stokke & Norum (LCAT S-N), by the method of Glomset & Wright (LCAT G-W), and by a method based on the measurement of free cholesterol by gas liquid chromatography (LCAT GLC). The precision of LCAT S-N and LCAT G-W was much poorer in samples with low than at normal activity. LCAT GLC was not precise enough to measure the variation in free cholesterol in normal plasma during the first 30 min of the reaction. A marked variation in LCAT activity was observed when different inactivated substrate sources were used. In plasma from 30 healthy men activity as measured by LCAT S-N was correlated with the concentration of free and esterified cholesterol, triglycerides, and alfa-lipo-protein. Activity as measured by LCAT G-W in these samples was correlated with the concentration of triglycerides, but not with free and esterified cholesterol. There was no decrease in activity in samples stored at 4 °C for 6 days, while only 70% of the initial activity was obtained after 15 days at this temperature. Samples could be stored at -15 ° for at least 4 months without decrease in LCAT activity. In two patients with liver disease an increase in free cholesterol was observed initially during incubation at 37 °C.