RAT MILK AND DIETARY LONG ARGININE(3) INSULIN-LIKE-GROWTH-FACTOR-I PROMOTE INTESTINAL GROWTH OF NEWBORN RAT PUPS

Newborn rat pups were artificially reared by the pup in cup (PIC) meth od to determine whether dietary long arginine(3) IGF-I (long R-3 IGF-I ), an IGF-I analog with high receptor affinity and low IGF binding pro tein (IGFBP) affinity, had efficacy on intestinal growth. IGF effects are mediated by IGFBP and receptor interactions, hence dietary-induced changes in intestinal IGF-II receptor patterns and IGFBP-3 message le vels were investigated. Intestinal micrographs of pups fed rat milk re placer (RMR) for 3 d showed flattened villi with low cell counts and a ppeared similar to newborn intestines. Mother-fed (MF) controls and lo ng R-3 IGF-I-fed pups showed increased villi height and cell counts wh en compared with RMR pups, with long R-3 IGF-I fed pups showing the gr eatest increase. At birth IGF-II-specific binding was not uniform in t he intestine; specific binding was higher in the proximal intestinal s ection than in the distal intestinal section. However, after 3 d of MF treatment, specific binding had reversed and the distal section showe d higher IGF-II-specific binding. Three days of RMR feeding did not ch ange IGF-II-specific binding from that of the newborn pup. An IGFBP-3 message was identified in intestinal epithelium by in situ hybridizati on. Northern analysis of IGFBP-3 message showed a decline over time, b ut the change was not influenced by dietary treatments. In summary, mi lk-borne growth factors have the potential to affect intestinal growth within 3 d of treatment.