EFFECT OF MEDIUM-CHAIN AND LONG-CHAIN TRIGLYCERIDE INFUSION ON LIPOPROTEIN AND HEPATIC LIPASE IN HEALTHY-SUBJECTS

Plasma lipolytic activity and hydrolysis of intravenous fat were studied in six healthy subjects during infusion of a long-chain triglyceride (LCT) fat emulsion (Intralipid 20%) or of a medium-chain triglyceride (MCT)/LCT emulsion (Lipofundin MCT 20%). The fat emulsions were infused continuously at a rate of 0.17 g triglyceride kg-1 body weight (BW) h-1 for 6 h in random order at 7-day intervals. A continuous infusion of glucose (0.18 g kg-1 BW h-1) was administered for a period of 7 h and was started 1 h before the lipid infusion. Infusions of both types of fat increased plasma triglyceride (TG), free fatty acid (FFA) and lipoprotein lipase (LPL) levels and steady-state values were present during the 3rd to 5th h of infusion. MCT/LCT infusion resulted in higher plasma levels at steady-state of TG (3.63 +/- 0.45 [SEM] vs 2.73 +/- 0.45 mmol l-1; P < 0.05), FFA (1.05 +/- 0.08 vs 0.54 +/- 0.04 mmol l-1; P < 0.01) and LPL (4.6 +/- 0.6 vs 2.6 +/- 0.5 mU ml-1; P < 0.05) in comparison with LCT administration. There was a positive correlation in between plasma LPL activity and TG concentration (r = 0.77; P < 0.001) when data for the two infusions were combined. Although the same amount of fat was infused on a weight basis, the molar infusion rate was 40% higher with MCT/LCT than with LCT infusion, due to differences in molecular weights (634 vs 885 Da). The increments in molar TG levels of both groups were comparable with differences in molar infusion rates, indicating that MCT/LCT and LCT fat were cleared at similar rates. After 5 h of lipid infusion 50 IU of heparin kg-1 BW was injected as a bolus dose to release endothelial lipases into the circulating blood. LPL activity increased approximately 90 times and reached 343 +/- 38 mU ml-1 during MCT/LCT and 226 +/- 22 mU ml-1 during LCT infusion (P < 0.01). It is concluded that the interaction between plasma TG and LPL activity is reciprocal. LPL activity is an important factor for regulating TG turnover and plasma TG affects LPL activity. On a molar basis, the two types (LCT and LCT/MCT) of fat emulsion were cleared at comparable rates.