Various types of the pituitary folliculo-stellate cells involving the Siperstein's corticotroph in the normal rats.

The differentiation of the folliculo-stellate (F-S) cells was electronmicroscopically investigated in the normal male adult rats from the Wistar, Wistar-Imamichi, Holzmann, Spraque-Dowley and Donryu strains. The F-S cells may be divided into the five types according to the granulation. Each type is, however, provided with the common characteristic features, i.e., the stellate shape due to projecting the cytoplasmic processes and a tendency to embrace an acidophil. The first type is an agranular independent or anastomosing immature cell. It is different in shape and arrangement from the follicular cell, but similar in agranularity and immaturity to it. The second is a slightly differentiated cell, in which scanty small secretory granules 50--100 nm in diameter begin to appear near the plasma membrane. The third is a moderately differentiated cell providing the regularly row arrangement of secretory granules 100--200 nm in diameter along the plasma membrane, corresponding, in fine structure, with a corticotroph. The fourth is a fully differentiated cell with heavy granulation, whose secretory granules 150--250 nm in diameter are accumulated in the whole cytoplasm, suggesting the storing type. It is difficult to determine whether the fourth type coincides with a hypergranulated corticotroph or a stellate thyrotroph. The fifth is a kind of fully differenetiated cell which may refer to the releasing phase of the fourth type, being characterized by the dispersion or loss of minute secretory granules of low density as large as 50 nm in diameter, associated with the cored vesicles. The population densith of the above five types increased in the sequence, 5th leads to 4th leads to 1st leads to 3rd type in the gland. Namely, the 3rd (corticotroph) type and 1st (agranular) type are predominantly distributed, and the 5th (releasing) type and 4th (hypergranulated) type are rarely.