Carnitine affects Octanoate Oxidation to Carbon Dioxide and Dicarboxylic Acids in Colostrum-Deprived Piglets: In Vivo Analysis of Mechanisms Involved Based on CoA- and Carnitine-Ester Profiles

Abstract

Newborn, colostrum-deprived piglets (n = 21) were used to study the effects of L-carnitine supplementation on the in vivo oxidation of [1-14C]octanoate to CO2 and dicarboxylic acids. Pigs were fitted with arterial and bladder catheters and were infused with octanoate (supplying 35–100% of piglets' energy expenditure) and with or without valproate for a period of 24 h. After achieving steady-state octanoate oxidation, carnitine was coinfused [50 µmol/kg0.75 prime plus 20 µmol/(h·kg0.75)], and deviations in the octanoate oxidation rate, dicarboxylic acid excretion rate, and carnitine metabolism were monitored. At the end of the 24-h infusion, samples of liver and muscle were analyzed for carnitine- and CoA-esters by HPLC. Carnitine stimulated octanoate oxidation by 7% (P < 0.05) and decreased dicarboxylic acid excretion by 45% (P < 0.05). Carnitine supplementation increased (P < 0.05) concentrations of carnitine and acetyl carnitine in hepatic tissue (three- and 55-fold, respectively) and plasma (seven- and 11-fold); whereas, muscle-carnitine concentration doubled upon carnitine supplementation, but acetyl carnitine concentration remained unaltered. Urinary excretion of acetyl and free carnitine also increased with carnitine supplementation, but accounted for <10% of carnitine infused. Hepatic total CoA and CoA esters increased with carnitine supplementation, whereas muscle acetyl-CoA decreased. Valproate had only marginal effects on octanoate metabolism. These data confirm the hypothesis that carnitine affects the in vivo oxidation of octanoate in colostrum-deprived piglets and suggest that the effects may be mediated by aiding the export of excess acetyl groups from muscle or by enhancing uptake of octanoate into liver mitochondria.