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 t o increase the protein accretion rate (PAR) in the neonatal small intestine . Seven-day-old piglets received an equal total daily intake of an elementa l diet, with different proportions given enterally (0, 10%, 20%, 40%, 60%, 80%, and 100%). After 7 days, piglets were infused intravenously with [H-2( 3)]leucine for 6 h, and the fractional protein synthesis rate (FSR) was mea sured in the proximal (PJ) and distal jejunum (DJ) and the proximal (PI) an d distal ileum (DI). The jejunal FSR increased from 45%/day to 130%/day bet ween 0 and 60% enteral intake, whereas the FSR in the ileum was less sensit ive to enteral intake level. At 0% enteral intake, PAR was significantly ne gative 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 t hat there is net intestinal protein loss at 0% enteral intake, protein bala nce at 20% enteral intake, and maximal intestinal protein accretion at 60% enteral intake.