Stability of insulin-like growth factor I in the gastrointestinal lumen in neonatal pigs.

BACKGROUND: Insulin-like growth factor (IGF)-I is present in the milk of various species. A prerequisite for any biological activity of milk-borne IGF-I in the suckling young is to survive the gastrointestinal luminal digestion. In the present study, the stability of IGF-I was examined in the gastrointestinal lumen in neonatal pigs.
METHODS: Iodine-labeled IGF-I was incubated in the gastrointestinal luminal fluids of 3-day-old suckling and 45-day-old weaned pigs at 37 degrees C for 20 minutes. Degradation of the peptide was analyzed by trichloroacetic acid (TCA) precipitation, liquid chromatography, and receptor binding assay.
RESULTS: IGF-I remained unchanged in the gastric fluids of suckling and weaned pigs when determined by TCA precipitation. IGF-I degraded 3%, 18%, and 37% in the luminal fluids of the proximal, mid and distal small intestine in suckling piglets compared with 53%, 62%, and 54% in weaned pigs. The results were supported by the chromatography and receptor binding analysis. Porcine colostrum had a capacity to protect IGF-I from gastrointestinal luminal digestion in weaned pigs.
CONCLUSION: Milk-borne IGF-I is stable in the gastrointestinal lumen in suckling pigs and may play a role in regulating postnatal development in the suckling young.