MEDIUM-CHAIN FATTY-ACID OXIDATION IN COLOSTRUM-DEPRIVED NEWBORN PIGLETS - STIMULATIVE EFFECT OF L-CARNITINE SUPPLEMENTATION

To investigate the role of L-carnitine in medium-chain fatty acid (MCF A, fatty acids with 6-12 carbons) metabolism, 16 newborn pigs were fit ted with umbilical arterial catheters. Pigs were placed in respiration chambers, and [1-C-14]MCFA were infused for 9-12 h providing energy e quivalent to 50-175% of the animals' metabolic rate. After 5-7 h (carn itine-free infusion period) of MCFA infusion, a primed (12.5, 25 or 50 mumol) co-infusion of L-carnitine [5, 10 or 20 mumol/(h.kg0.75), resp ectively] was started and maintained for 4-5 h (carnitine infusion per iod). The fatty acid oxidation rate (MCFA-derived CO2/total CO2 x 100) was calculated based on the specific radioactivity of expired CO2 (me asured per 20-min interval) and the specific radioactivity of the MCFA infused. A single-pool exponential curve was fitted to the fatty acid oxidation rate of the carnitine-free infusion period and was extrapol ated to the carnitine infusion period. For each piglet, the average di fference between fatty acid oxidation rate during the carnitine infusi on period and the extrapolated curve was calculated and tested for sig nificance using a t test. Under steady state conditions, MCFA oxidatio n accounted for 40% of MCFA infused. Carnitine, independent of the lev el, increased the fatty acid oxidation rate by as much as 20% if the e nergy provided as MCFA exceeded 50% of the metabolic needs of the pig (P < 0.01), and the response above 50% was proportional to the relativ e rate of fatty acid infusion (increase in fatty acid oxidation rate = -3.9 + 0.07 x infusion rate, r 0.76). Given the potential for carniti ne to increase MCFA oxidation in vivo, more research may warrant inclu sion of carnitine in nutrition solutions containing MCFA.