Ultrastructure of Crooke's cells with special reference to their secretory granules.

Twenty-seven postmortem pituitary glands were electron microscopically investigated. Eighteen of them revealed an accumulation of fine microfilaments in the cytoplasm ranging from 70 to 80 A in width, which is equivalent to a hyaline change in Crooke's cells seen with a light microscope. Since Crooke's changes were immunohistochemically evidenced to occur exclusively in ACTH cells, we examined their secretory granules quantitatively and concluded that the majority of them were ovoid, homogeneously electron dense and measured 200 to 450 nm in diameter averaging 332 nm. Occasionally, those irregularly shaped and larger than 600 nm were observed.