Electron microscopic studies on the anterior pituitary cells following castration in fetal and neonatal male rats

Electron microscopic examination was made on the cells of the anterior pituitaries in normal or castrated late fetal and early neonatal male rats. It was posbible to distinguish three types of granular cells in addition to celld of uncertain identity, on the basis of the diameters of granules. Type I cells had granules with a small range of diameters (40-180nm). Secretory granules of these cells were located mainly in the periphery of the cytoplasm. The cisternae of rough endoplasmic reticulum (RER) were flattened and irregularly arranged. Type II cells had somewhat larger granules (40-200nm) than type I cells. Granules of type II cells were located throughout the cytoplasm. The RER cisternae appeared as vesicular or short plates, or were grouped as lamellar stacks. Type III cells had granules with the widest range of diameters (90-360nm). Following castration, both type I cells and type III cells showed little cytological changes, but type II cells exhibited extreme changes accompanied by a marked enlargement of the RER cisternae and the Golgi complex. Such changes in type II cells were more marked in fetused than in neonatal rats, and were prevented by an injection of testosterone propionate. These observations support the view that type II cells include gonadotrophs and that the pituitary gonadotrophic activity declines just after birth in male rats.