Immunohistochemical localization of insulin in the chick embryo during development

Since an extrapancreatic source of insulin has been postulated in the chick embryo, insulin was sought by immunohistochemistry in the embryo before and after development of the pancreas and other tissues. Using for the first time an antiserum specific for chicken insulin, localization of insulin was investigated in whole embryos (Days 1-8) and in brain, kidney, liver, and pancreas (Days 9-21 and 30). Results indicate the presence of immunoreactive insulin in pancreatic islets from Day 5 onward with an increase in staining intensity during development. Insulin was not detected in other tissues of the early developing embryo or in brain, liver, or kidney in later development. These data suggest that although extrapancreatic insulin has been reported, concentrations are not high enough in tissues to be detected with a specific, homologous antiserum and sensitive immunohistochemical techniques.