EMULSIFICATION AND FATTY-ACID CHAIN-LENGTH AFFECT THE KINETICS OF [C-14] MEDIUM-CHAIN TRIACYLGLYCEROL UTILIZATION BY NEONATAL PIGLETS

In vivo oxidation kinetics of medium-chain triglycerides (MCT) compose d of [1-C-14]hexanoate (tri-6:0) or [1-C-14]octanoate (tri-8:0) were c ompared after being fed to day-old piglets (1.4 kg; n = 4/treatment). Animals were fitted with arterial anti ore-gastric catheters and place d into respiration chambers held at 35 degrees C. The radiolabeled MCT were fed in equimolar amounts (6.5 mmol/kg(0.75)), in either nonemuls ified form or as 30% (v/v) emulsions, using polyoxyethylene sorbitan m onooleate as an emulsifier. Expired CO2 was quantified and specific ra dioactivity (Bq/mu mol) determined at 20-min intervals over 24 h, and serial blood samples were drawn for measurement of plasma hexanoate an d octanoate by HPLC. The rate [mu mol/(h.kg(0).(75))] and extent (mmol /kg(075)) of MCT oxidative utilization (i.e., composite of digestion, absorption and oxidation) were calculated from the kinetics of (CO2)-C -14 expiration. Emulsification increased both the rate and extent of M CT oxidative utilization by >20% regardless of fatty acid chain length (P < 0.05). Maximal MCT oxidation rates occurred at 3.5 h after feedi ng and were sufficient to meet up to 48% of the piglets' energy expend iture. The maximal rate of tri-6:0 oxidative utilization exceeded that of tri-8:0 by 37% (P < 0.05), but the extent of utilization was not a ffected by fatty acid chain length. Plasma medium-chain fatty acid con centrations were in agreement with these observations, being higher in pigs fed emulsified MCT than in pigs fed nonemulsified MCT (P < 0.05) and being higher in pigs fed tri-6:0 than in animals fed tri-8:0 (P < 0.05). Collectively, these data demonstrate that newborn piglets can effectively digest, absorb and oxidize MCT, that utilization is improv ed with emulsification, and that tri-6:0 is utilized more rapidly than tri-8:0.