A, B, D cells and a fourth cell type in long-term cultures of fetal rat pancreas.

Whole pancreases from fetal rats of 13 days and 18 days gestation were explanted onto rayon grids and grown in organ culture. Cultures were fixed in Bouin's fluid, sectioned and stained with the fluorescent antibody techniques for glucagon and insulin, aldehyde fuchsin for B cells, pseudoisocyanin for D cells and a silver technique for the fourth cell type. The 13-day explants were fixed after 10 days in culture. A, B and D and the fourth cell type were seen, indicating that precursors of all four endocrine cell types must be present in the fetal pancreas shortly after the formation of the pancreatic bud (11 days). Further, the presence of these four cell types in the walls of tubules in these cultures indicates the tubules as the site of origin of all the endocrine tissue. The 18-day explants were collected every other day of culture from 2 to 30 days in a long-term experiment. A number of large islets with well granulated B cells was still present after 30 days of culture. The relative abundance of cell types at different stages was estimated as follows: 18-day fetal controls, A greater than B=4 greater than D; after 2 to 10 days in culture, B greater than A greater than or equal to D; after 18 to 30 days in culture, B greater than D greater than A greater than 4.