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

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Abstract
Differentiation of folliculo-stellate (F-S) cells was investigated via EM in normal, male, adult rats from the Wistar, Wistar-Imamichi, Holtzman, Sprague-Dawley and Donryu strains. The F-S cells may be divided into 5 types according to the granulation. Each type is, however, provided with common characteristic features, i.e., stellate shape due to projecting cytoplasmic processes and a tendency to embrace an acidophil. The 1st type is an agranular independent or anastomosing immature cell. It is different in shape and arrangement from the follicular cell, but similar to it in agranularity and immaturity. The 2nd is a slightly differentiated cell, in which scanty, small secretory granules 50-100 nm in diameter begin to appear near the plasma membrane. The 3rd is a moderately differentiated cell providing the regular row arrangement of secretory granules 100-200 nm in diameter along the plasma membrane, corresponding, in fine structure, with a corticotroph. The 4th 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 4th type coincides with a hypergranulated corticotroph or a stellate thyrotroph. The 5th is a kind of fully differentiated cell which may refer to the releasing phase of the 4th 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 density of the 5 types increased in the sequence, 5th .fwdarw. 4th .fwdarw. 2nd .fwdarw. 1st .fwdarw. 3rd type in the gland. The 3rd (corticotroph) type and 1st (agranular) type are predominantly distributed, and the 5th (releasing) type and 4th (hypergranulated) type are rare.