[Parenterally administered medium-chain triglyceride-induced changes in carnitine metabolism]

Medium-chain triglycerides are generally assumed to be metabolized independently of carnitine. The effects of infusing medium-chain triglycerides on plasma concentrations of carnitine derivatives and beta-hydroxybutyrate was studied in four healthy male adults. Glucose and amino acids were infused alone for three hours, then continued for another 5.5 hours together with a lipid emulsion containing only long-chain triglycerides or a mixture of medium-chain and long-chain triglycerides (50:50; w/w). During the fat-free infusion, the concentration of free carnitine rose, while the level of acylcarnitines decreased. Infusion of the mixed emulsion over 5.5 hours reduced free carnitine to lower values (32.4 +/- 4.7 mumols/L) than long-chain triglycerides infusion (44.4 +/- 2.7 mumols/L). By contrast, the plasma concentrations of short-chain acylcarnitines (12.1 +/- 3.3 vs. 5.4 +/- 1.9 mumols/L; p less than 0.01) and of beta-hydroxybutyrate (93 +/- 32 vs. 47 +/- 14 mumols/L; p less than 0.01) became significantly higher with the mixed emulsion than with long-chain triglycerides. These findings suggest that oxidation of medium-chain fatty acids is to some extent carnitine-dependent, whether or not transport into mitochondria is carnitine-mediated.