Ontogenetic appearance of immunoreactive endocrine cells in rat pancreatic islets.

Chronological development of immunoreactive, pancreatic endocrine cells was immunohistochemically studied in rats. The first immunoreaction occurs for glucagon on day 11.5 and for insulin on day 12.5 of gestation, respectively, in the cells located within the cap-like or tubular pancreatic primordium derived from the gut wall. Immunoreactive somatostatin cells appear first at the periphery of primitive islets on day 15.5. On day 18.5, the cells of the primitive islets obtain their definite arrangement and the islets are now separated from the tissue of the exocrine pancreas. Decapitation or encephalectomy performed on day 16.5 embryos fails to influence the ensuing further development of endocrine pancreas. This suggests that the hypothalamus or pituitary does not play an essential role in the histogenesis of the pancreatic islets.