Prenatal development of the human pancreatic islets. Immunocytochemical identification of insulin-, glucagon-, somatostatin- and pancreatic polypeptide-containing cells.

Histological studies were performed on 24 pancreases of normal human embryos and fetuses aged 7 to 38 weeks. For immunocytochemistry, the avidin-biotin-peroxidase method was used to identify and localize insulin, glucagon, somatostatin, and pancreatic polypeptide (PP) cells. In 7 wk old embryos, cells containing somatostatin and PP are observed. One week later appear single glucagon-positive cells. In the 9th wk, insulin producing cells are visible. During the fetal period two populations of the investigated cells are found: Langerhans islets and dispersed cells. The latter cells containing insulin, glucagon or somatostatin are localized in the walls of pancreatic ducts throughout the whole gland, while PP-positive cells are seen mainly in the part of the pancreas, which develops from the ventral anlage (anteroinferior part of the head and adjacent part of the main pancreatic duct). During the development of islets we have observed four stages: (1) scattered cells (7 to 10 weeks); (2) grouping cells (11 to 15 weeks); (3) mantle and zonular islets (10 to 29 weeks), in which B cells located inside are surrounded by a thick zone of A, PP and somatostatin-producing cells; (4) mixed islets (from 30 weeks on) - all cells are scattered over the whole transverse section of the islet. In the developing pancreas, the glucagon- and somatostatin-containing cells are the most numerous, while the insulin and PP-containing cells occur in lesser quantities.