Nutritional modulation of insulin-like growth factor-I expression in early postnatal piglets

The roles of intrauterine growth retardation, energy intake, and food composition in determining circulating and hepatic concentrations of IGF-I in early postnatal life have been determined. Intrauterine growth-retarded, small-for-gestational-age piglets were kept at thermal neutrality and fed sow's milk replacement formula to repletion at 6-h intervals between 2 and 14 d of age. When their appropriate-for-gestational-age littermates were pair-fed this intake, there were no significant differences in plasma or hepatic concentrations of IGF-I. Thus, under conditions of controlled food intake, prenatal undernutrition does not affect the postnatal expression of IGF-I. However, when appropriate-for-gestational-age piglets were fed to repletion at 6-h intervals over the 12 d, they had a significantly greater hepatic IGF-I concentration (p < 0.002) and food intake (p < 0.001) than the small-for-gestational-age piglets, indicating a critical role for food intake regulation in catch-up growth. Striking differences in growth rate and IGF-I expression were also found between formula-fed, appropriate-for-gestational-age piglets compared with animals left with the sow. The latter grew much more rapidly (p < 0.0001) and had considerably higher levels of plasma IGF-I (p < 0.0001) despite similar hepatic IGF-I concentrations. Differences in plasma IGF-I may have been caused by the high level of IGF-I in maternal milk, by differences in hepatic synthesis and release, or by altered profiles of IGF binding proteins and hence in altered IGF-I clearance from plasma.(ABSTRACT TRUNCATED AT 250 WORDS)