DEVELOPMENTAL APPEARANCE OF PEPTIDE-BINDING SITES IN THE SMALL-INTESTINE OF THE NEONATAL PIGLET

The ontogeny of the expression of specific binding sites for bombesin (BBS), vasoactive intestinal polypeptide (VIP), and gastrin in the neo natal pig was examined. Piglets were sacrificed at birth, 1 d, 1 wk, 3 wk and 4 wk, and samples of duodenal, jejunal and ileal tissue were h arvested for autoradiographic analysis of saturable radioligand bindin g. Monoiodinated, biologically active I-125-Tyr4-BBS, VIP or gastrin ( 100 pM) was applied to slide-mounted sections of piglet intestinal tis sue and localized using autoradiographic analysis of radioligand bindi ng. Saturable binding sites for I-125-BBS first appeared in duodenal t issue of 7-d-old piglets, with evidence for continued presence in this tissue through 21 d. BBS binding sites were localized in duodenal muc osa, with no detectable binding in any other tissue layers. No evidenc e for saturable binding of I-125-Tyr4-BBS was found in intestinal sect ions from either newborn, 1-d-old or 4-wk-old piglets. Saturable bindi ng sites for I-125-VIP were present in duodenal, jejunal and ileal tis sues of piglets at all ages studied and were present in both the mucos a and the muscularis externa. No saturable binding sites for I-125-gas trin were observed in intestinal sections from piglets at any of the a ges studied. These results suggest potential sites of direct action of VIP in newborn, suckling and newly weaned piglets. Bombesin, however, may have direct actions only on the duodenal mucosa at 7-21 d of age.