Enteral nutrient intake level determines intestinal protein synthesis and accretion rates in neonatal pigs

Our objective was to determine the minimum enteral intake level necessary to increase the protein accretion rate (PAR) in the neonatal small intestine. Seven-day-old piglets received an equal total daily intake of an elemental diet, with different proportions given enterally (0, 10%, 20%, 40%, 60%, 80%, and 100%). After 7 days, piglets were infused intravenously with (2)H(3)leucine for 6 h, and the fractional protein synthesis rate (FSR) was measured in the proximal (PJ) and distal jejunum (DJ) and the proximal (PI) and distal ileum (DI). The jejunal FSR increased from 45%/day to 130%/day between 0 and 60% enteral intake, whereas the FSR in the ileum was less sensitive to enteral intake level. At 0% enteral intake, PAR was significantly negative in the PJ, DJ, and PI (range -70 to -43 mg/day) and positive in the DI (49 mg/day), whereas intestinal protein balance occurred at 20% enteral intake. At 100% enteral intake, the PAR was greatest in the DI, even though the rates of protein turnover were 50% lower than in the PJ. We conclude that there is net intestinal protein loss at 0% enteral intake, protein balance at 20% enteral intake, and maximal intestinal protein accretion at 60% enteral intake.