An immunocytochemical study of endocrine cell development in the early fetal guinea pig pancreas

The presence of insulin, glucagon, pancreatic polypeptide, and somatostatin containing cells and their ontogenic changes were investigated immunocytochemically in the early fetal pancreas of the guinea pig (Days 25-40). In the earliest tissues examined (Day 25 and Day 30) brightly staining glucagon cells were the most predominant endocrine cell population, followed by slightly fewer and weaker staining pancreatic polypeptide cells. Insulin and somatostatin immunoreactive cells were less numerous. At Day 25 all endocrine cells were located within the pancreatic tubules where some glucagon cells also coexpressed insulin. Similar dual immunoreactivity was present at Day 30. At Day 25 some of the pancreatic polypeptide cells also showed coexpression of somatostatin which persisted until Days 35-40. At these later stages insulin and somatostatin cells were increasingly frequent. Glucagon and pancreatic polypeptide cells were also conspicuous. The four endocrine cell types were found either in the pancreatic tubules or in the developing islets where they began to acquire an adult-like topographic distribution. These studies in the fetal guinea pig show that the four islet hormonal cells cytodifferentiate from an early stage. A small proportion of endocrine cells coexpress either insulin and glucagon or pancreatic polypeptide and somatostatin.