Evaluation of [1-14C]-medium-chain fatty acid oxidation by neonatal piglets using continuous-infusion radiotracer kinetic methodology.

In vivo oxidation rates of systemically infused medium-chain fatty acids were evaluated using neonatal pigs. Unanesthetized piglets (1.6 kg, n = 20) were housed in respiration chambers for total collection of expired CO2 and were continuously infused with [1-14C]-7:0, 8:0, 9:0 or 10:0 fatty acids via a central catheter. The fatty acids were administered at rates of 25, 50 or 100 mumol/min for 5 h and provided 74 kBq of 14C per h. Total expired CO2 was collected over consecutive 15-min intervals for determination of the amount and specific radioactivity of expired CO2. Portal blood samples were drawn from umbilical vein catheters for determination of 3-hydroxy-butyrate and plasma fatty acid concentrations. Infusion and oxidation rates (mmol/min) were multiplied by the molar ATP yield for each fatty acid (i.e., 52, 61, 69 and 78 mmol ATP/mmol fatty acid for 7:0 through 10:0, respectively) to adjust for differences in molar energy content of the various fatty acids. Expressed in this way, fatty acid oxidation rate was proportional to the rate of infusion and accounted for 63% of that infused. The various fatty acids were oxidized equally well, regardless of chain length, and satisfied up to 60 to 70% of the animals' energy requirements, depending on the rate of infusion. These data are discussed in relation to previous work from our laboratory that has shown significant effects of fatty acid chain length on utilization of orally administered medium-chain triglyceride supplements.