Influence of Fat Ingestion on Lecithin:Cholesterol Acyl Transfer Rate in Plasma of Normal Persons

Abstract

Lecithin:cholesterol acyl transfer (LCAT) rate in plasma and lipid concentrations in total plasma and high density lipoproteins (HDL) were determined before and after oral fat loads in healthy human subjects. The changes of LCAT rate after fat loading were compared to the effect of chylomicrons or lipid emulsions added in vitro to fasting plasma. After the fat loads there was an increase of mean molar LCAT rate simultaneous with an increase of mean phospholipid (PL) and HDL-PL concentration but not simultaneous with the increase of mean triglyceride (TG) concentration. Individual changes of molar LCAT rate correlated positively with changes of PL, HDL-PL, and unesterified cholesterol (UC) concentration but not with changes of TG concentration in the separate plasma samples after the fat loads. If only the maximal changes in each subject in any sample at any time after the loads were taken into account, the maximal increase of molar LCAT rate correlated positively with the maximal increase of TG concentration. Molar LCAT rate was not influenced by addition of chylomicrons in vitro but increased after addition of a PL emulsion. It is suggested that LCAT rate is stimulated by an excess of PL in plasma and substrate lipoproteins. This excess of PL may be created in vivo temporarily during chylomicron catabolism. The stimulation of LCAT rate by fat ingestion emphasizes the importance of LCAT as a connecting link between triglyceride and cholesterol metabolism.