Electron microscopic studies on the anterior lobe cells of the frog hypophysis, with special regard to the identification of the ACTH-cell.

Abstract

The pars distalis of normal, adrenalectomized, metopirone-administrated and sham-operated frogs was observed with the electron microscope. Based on the size, shape and internal structure of secretory granules and on the ultrastructural characteristics, seven cell types are classified.Type 1 is a large spherical or oval cell containing spherical secretory granules, 600-1, 200mμ in diameter. Type 2 is a spherical or oval cell containing spherical secretory granules, 400-600mμ in diameter. Type 3 is a polygonal cell containing a few spherical secretory granules, some of which are cored granules, 200-350mμ in diameter. This type cell is less numerous than the others. Type 4 is an oval or cylindrical cell containing spherical secretory granules, 150-250mμ in diameter. Type 5 is a large spherical or oval cell containing spherical and rod-shaped secretory granules, 300-1, 200×300-600mμ in long and short diameters. The spherical granules are similar to those in the type 1 cell. Type 6 is an oval or cylindrical cell containing spherical and rod-shaped secretory granules, 300-400×100-300mμ in long and short diameters. The spherical granules are similar to those in the type 2 cell. Type 7 is a stellate cell without any secretory granules. Many cytoplasmic processes extend to the blood capillary.After bilateral adrenalectomy, the type 3 cell shows marked changes in its cytoplasm. The secretory granules are extremely decreased in number, and the rough-surfaced endoplasmic reticulum and the Golgi apparatus become well developed. New granular formation is frequently found in the Golgi area. After the administration of an adrenocortical inhibitor, metopirone, similar fine structural changes are recognized in type 3 cells. These findings suggest that the type 3 cell of the frog pars distalis may secrete adrenocorticotrophic hormone (ACTH).