Fine structural criteria for identifying rat corticotrophs.

The fine structural characteristics of normal rat corticotrophs stained with anti-porcine ACTH1-39 serum were studied. At the ultrastructure level immunoreactive corticotrophs appear to comprise four distinct cell types: (1) large stellate cells (Siperstein cells) containing granules (170-250 nm in diameter) arranged in a peripheral row and usually embracing an acidophil; (2) elongate spindle-shaped cells (Moriarty cells) in which the secretory granules (170-250 nm in diameter) are distributed in a row or in small clusters in the peripheral cytoplasm: (3) oval or polygonal cells filled only with small secretory granules (130-170 nm in diameter), resembling the "acidophil of small granules type" (Yoshimura et al. 1974); and (4) polygonal or stellate cells filled with secretory granules of varying diameters (180-300 nm in diameter) and occasionally embracing an acidophil. The first type is the most common, but the others are infrequent. It is concluded that the criteria of Siperstein and Miller (1970) do not necessarily include all categories of rat corticotrophs.