Histological and immunohistochemical studies of the Segi's cap, a large aggregation of endocrine cells on the intestinal villi of porcine fetuses and neonates.

Segi's cap, a large aggregation of endocrine cells on the top of intestinal villi, was studied in porcine fetuses and neonates by histological and immunohistochemical methods. The following observations were made: 1) Segi's caps were found in the proximal small intestine in all fetuses larger than 17 cm (beyond 10 weeks of gestation), in neonates before suckling and in 1-4 day-old piglets (suckling neonates); they were not found in a 1 week-old animal. 2) Segi's caps were seen more frequently in the distal duodenum and proximal jejunum than in the proximal and middle duodenum. 3) The Segi's cap consisted mainly of numerous argyrophil cells as demonstrated by Grimelius' method and a few argentaffin cells as identified by a modified Masson-Hamperl's method. 4) Immunohistochemically, ten kinds of immunoreactive cells were dispersed in the mucosal epithelium, outside of Segi's caps, in the proximal small intestine of fetuses: 5-hydroxytryptamine (5-HT)-, gastrin-, bovine pancreatic polypeptide (BPP)-, secretin-, somatostatin-, cholecystokinin-, gastric inhibitory polypeptide (GIP)-, motilin-, leucine-enkephalin- and neurotensin-immunoreactive cells. Except for neurotensin-immunoreactive cells, all of these cells were detected also in the caps. 5) Regional differences were noted in the distribution of cells in the caps; gastrin-, BPP- and secretin-immunoreactive cells were dominant in the caps in the proximal duodenum, while 5-HT-immunoreactive cells were most numerous in those in the proximal jejunum.