Intrauterine growth restriction does not alter response of protein synthesis to feeding in newborn pigs

This study aimed to determine the effect of intrauterine growth restriction (IUGR) on the acute response of tissue protein synthesis to feeding in newborn pigs. Newborn pigs of sows fed either control or protein-restricted diets throughout gestation were designated C or IUGR, respectively. Both groups were either fasted for 9 h after birth or fed hourly 30 ml colostrum/kg body wt for 2.75 h after a 6-h fast. Fractional rates of tissue protein synthesis (Ks) were measured in vivo with a flooding dose of L-[4-3H]phenylalanine. Birth weight was reduced by 33% in IUGR pigs. IUGR had no effect on Ks in skeletal muscles, heart, liver, jejunum, or pancreas. Feeding stimulated tissue Ks similarly in C and IUGR pigs. Fasting plasma insulin concentrations and their rise with feeding were unaffected by IUGR. Plasma insulin-like growth factor I (IGF-I) concentrations were reduced by 42% in IUGR pigs and were not altered by feeding in either IUGR or C pigs. There were positive nonlinear relationships between tissue Ks and circulating concentrations of insulin. The results indicate that, in newborn pigs, tissue Ks are unaffected by IUGR, despite reduced plasma IGF-I concentrations. The efficiency with which nutrients stimulate tissue Ks is also not altered by IUGR, perhaps because the rise in plasma insulin concentrations with feeding is unaffected by IUGR.