Ontogeny of gastric inhibitory peptide in the human gastro-intestinal tract and endocrine pancreas

The appearance and distribution of the gastro-intestinal hormone, gastric inhibitory peptide (GIP) were examined in the gastro-entero-pancreatic system of human foetuses, aged 5–24 weeks, by immunocytochemistry or radioimmunoassay. The first immunoreactive cells were observed in the gut from 16 weeks of gestation. The GIP-containing cells were localized preferentially in the villous epithelium of the small intestine. In the radioimmunoassay, the highest concentrations of immunoreactive GIP (IR-GIP) were detected from 13 to 21 weeks of gestation. The tissue concentration of IR-GIP was 68.10 ± 10.70 ng/g wet weight of duodenum, 30.29 ± 3.96 ng/g wet weight of jejuno-ileum and 3.05 ± 1.97 ng/g wet weight in the colon. Measurable amounts of IR-GIP (4.93 ± 1.57 ng/g wet weight of organ) were found from 9 to 12 weeks in the jejuno-ileal region. The ontogenic development of IR-GIP was studied in this region. From 13 to 21 weeks of gestation, the IR-GIP content per g of organ increased about 6-fold. In the endocrine pancreas, GIP antiserum No. R07 was potent in staining A cells from 14 weeks of gestation. In radioimmunological tests, no cross-reactions of the anti-GIP sera R 07 and GP 01 with heterologous peptides were observed. Labelling of paraffin and semi-thin sections was subjected not only to the usual specificity tests, but also to particularly extensive cross-reaction studies. GIP-like immunoreactivity was not inhibited by absorptions against heterologous peptides added at varying concentrations. The immunocytological and radioimmunological results are consistent with an eventual implication of GIP in the endocrine regulation of metabolism or in the development of the gastro-entero-pancreatic system during the intrauterine life in man.