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 neonatal 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 harvested for autoradiographic analysis of saturable radioligand binding. Monoiodinated, biologically active 125I-Tyr4-BBS, VIP or gastrin (100 pM) was applied to slide-mounted sections of piglet intestinal tissue and localized using autoradiographic analysis of radioligand binding. Saturable binding sites for 125I-BBS first appeared in duodenal tissue of 7-d-old piglets, with evidence for continued presence in this tissue through 21 d. BBS binding sites were localized in duodenal mucosa, with no detectable binding in any other tissue layers. No evidence for saturable binding of 125I-Tyr4-BBS was found in intestinal sections from either newborn, 1-d-old or 4-wk-old piglets. Saturable binding sites for 125I-VIP were present in duodenal, jejunal and ileal tissues of piglets at all ages studied and were present in both the mucosa and the muscularis externa. No saturable binding sites for 125I-gastrin were observed in intestinal sections from piglets at any of the ages 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. Key words: Bombesin, vasoactive intestinal polypeptide, gastrin, piglet, small intestine, newborn