Fine structure of foetal rat pancreatic alpha and beta cells at term and during prolonged gestation.

The fine structure of the foetal rat pancreatic alpha and beta cells was described at term (Day 22) and during prolonged gestation (Days 23, 24, and 25). Gestation was prolonged by daily subcutaneous injections of progesterone to the mothers from Days 20 through 24 of pregnancy. Alpha and beta cells at term contained numerous secretory granules and well developed cytoplasmic organelles. During prolonged gestation (Days 24 and 25 only) the beta cells exhibited an increased number of secretory granules whereas the alpha cells revealed decreased numbers of secretory granules and increased numbers of Golgi saccules and associated vesicles. In addition a few alpha cells contained numerous secretory granules which were concentrated toward the cell surface nearest a capillary. The results were discussed with respect to what role foetal alpha and beta cells might have in foetal glucose homeostasis during prolonged gestation.