Ontogeny of vasoactive intestinal peptide in the human fetal digestive tract

Immunocytochemistry and radioimmunoassay were used to assess the appearance time and tissue distribution of vasoactive intestinal peptide (VIP) in the digestive tract of the human fetus. By radioimmunoassay, VIP was measurable from 10 weeks of gestation. The peptide was abundantly distributed in the jejuno-ileum and colon, where the tissue peptide concentration rose from 9–14 weeks of gestation (18.4 ± 4.4 and 22.0 ± 5.0 pmol/g wet weight, respectively) to 15–21 weeks (83.0 ± 21.1 and 98.6 ± 36.4 pmol/g, respectively). Lower concentrations were recorded in pancreas from 9–14 weeks of gestation (4.3 ± 0.8 pmol/g) to 15–21 weeks (13.9 ± 3.7 pmol/g). The peptide concentration was 15.6 ± 1.9 pmol/g in fundus and 25.5 ±3.2 pmol/g in antrum from 15 to 21 weeks of gestation. The highest concentration was recorded in duodenum from 15 to 21 weeks of gestation 118.4 ± 40.8 pmol/g wet weight). Tissue VIP concentration and age were positively correlated in the jejunoileum. By immunofluorescence, immunoreactive VIP was localized in nervous fibers in the muscularis externa, in the submucosa and in the lamina propria. Scarce cell bodies were also found in the myenteric plexus. No immunofluorescent endocrine cells were observed. These results suggest: (1) the early appearance of immunoreactive VIP in gut, as early as 10 weeks of gestation; (2) the peptide, localized in nervous structures only, follows the same distribution pattern as that in adults; (3) the development of VIPergic structures is a continuous process, initiated during the 3rd month of pregnancy.