Nutrient Metabolism Medium-Chain Fatty Acids but Not L-Carnitine Accelerate the Kinetics of [C]Triacylglycerol Utilization by Colostrum-Deprived Newborn Pigs

The effect of L-carnitine on in vivo fatty acid utilization was determined using colostrum-deprived newborn piglets fed emulsified triglycerides (TG) composed of [1-C]octanoate (tri-8:0) or [1-C]octadecanoate (tri-18:1). A soy protein–based liquid diet devoid of L-carnitine was fed piglets for 1 d to allow development of fatty acid–metabolizing enzymes and intestinal fat digestion and absorption before assessment of in vivo fat utilization. The radiolabeled TG were fed in isoenergetic amounts (97.7 kJ/kg), with or without L-carnitine (1 mmol/kg) as 30% (v/v) emulsions, using polyoxyethylene sorbitan monooleate as an emulsifier. Expired CO2 was quantified and specific radioactivity (Bq/ mol) was determined at 20-min intervals over 24 h. The rate (mmol ATP kg 0.75 min ) and extent (mol ATP/kg) of TG oxidative utilization (i.e., composite of digestion, absorption and oxidation) were calculated from the kinetics of CO2 expiration. The maximal rate and extent of tri-8:0 oxidation were three and fourfold greater than those of tri-18:1, respectively (P 0.001), and tri-18:1 delayed the time to reach 10 and 50% of maximal oxidation rate by 1.2 and 1.9 h (P 0.01, respectively), regardless of supplemental carnitine. Collectively, these findings quantify the accelerated oxidation of medium-chain vs. longchain triglycerides, but fail to support a need for supplemental carnitine to maximize fat oxidation in colostrumdeprived piglets. J. Nutr. 132: 1989–1994, 2002.