[Electron microscopic study on the structure and the function of the granulosa cell in the human...

The cytodifferentiation, subcellular steroidogenic sites in the granulosa cell of the developing follicle were investigated using electron microscopic cytochemistry. The follicular cell in the primordial follicle already had a few lipid droplets. In the secondary follicle, the granulosa cell had a round nucleus, rough endoplasmic reticulum, lipid droplets, Golgi apparatus, microfilament, rod-shaped mitochondria with lamellar cristae and a small amount of smooth endoplasmic reticulum. In particular, the granulosa cell in the preovulatory follicle considered to be a transitional form to the steroid-secreting cell was characteristic of rough endoplasmic reticulum, lipid droplets, mitochondria with lamellar or tubular cristae and moderately well developed smooth endoplasmic reticulum. On the other hand, the granulosa cell in the postovulatory follicle revealed a typical steroid-secreting activity showing abundant lipid droplets, round mitochondria with tubular or vesicular cristae, well developed smooth endoplasmic reticulum and lysosomes. Reaction products for 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) activity were localized on tubular or lamellar cristae and inner membrane of the mitochondria, and on the membrane of smooth endoplasmic reticulum in the granulosa cell of the preovulatory as well as of the postovulatory follicle. From these facts, it is suggested that the granulosa cell in the preovulatory follicle already has a steroid-secreting activity and might play an important role in human reproduction.