Energy Expenditure in Rats Maintained with Intravenous or Intragastric Infusion of Total Parenteral Nutrition Solutions Containing Medium- or Long-Chain Triglyceride Emulsions

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Abstract
Energy expenditure was determined in male Fischer 344 rats (235–246 g) fed by intravenous (IV) or intragastric (IG) infusion with total parenteral nutrition solutions providing 65% of nonprotein energy as fat from long-chain triglyceride (LCT) or a 3:1 admixture of medium-chain triglyceride (MCT) and LCT emulsions. Respiratory gas exchange and somatomotor activity were assessed continuously for 24 h during d 5 and 11 of infusion feeding. The MCT infusion resulted in one-third the weight gain noted with LCT infusion (MCT, 10 ± 2 g/14 d; LCT, 32 ± 4 g/14 d; P < 0.0001). Insulin concentration was 60% higher with IV than with IG infusion and ∼100% higher with IV-MCT than with IG-MCT or LCT infusion (P < 0.05). Rats receiving IV infusion of MCT displayed similar levels of motor activity but 8–13% greater daily energy expenditure (kJ·kg-0.75·kJ intake-1) than rats receiving IG-MCT or LCT infusion (P < 0.05). The MCT infusion also resulted in an elevation in respiratory quotient after cessation of nutrient infusion (MCT, 0.87–0.92; LCT, 0.83–0.85; P < 0.05). Total and resting energy expenditure decreased ∼13% from 5 to 11 d of infusion feeding. The lower weight gain and greater energy expenditure seen with MCT- compared with LCT-supplemented total parenteral nutrition may be mediated by higher insulin concentrations.