Ultrastructural study of two gonadotrophs in rats bearing an adrenocortical carcinoma (Snell 494).

Two morphologically distinct gonadotrophs have been identified in the anterior pituitary of rats bearing the Snell 494 tumor. Type 1 gonadotrophs first showed ultrastructural alterations at 4 weeks after implantation of the tumor. Numerous large 300 to 600 mmu granules appeared in type 1 cells. The opacity of the granules was variable, and they sometimes contained non-membrane-bounded spherical inclusions. These granules were dispersed among more electron-opaque, 200-mmu granules usually seen in gonadotrophs. A third granule approximately 500 to 600 mmu in diameter was apparently a lysosome-derived structure. Type 2 gonadotrophs first showed changes after 4 weeks, but the alterations were especially prominent by 8 to 10 weeks. No large granules characteristic of type 1 cells were seen in type 2 cells. By 8 to 10 weeks, very few 200-mmu granules were observed in the cytoplasm of type 2 cells. The endoplasmic reticulum was dilated in most type 2 cells; frequently, the cisternae were dilated considerably, forming large lake-like areas. Hypertrophic rough endoplasmic reticulum and the presence of intracisternal granules within cisternae of the rough reticulum suggest that type 2 cells were stimulated by the tumor. Changes in gonadotrophs were undoubtedly produced by the large amount of corticosterone secreted by the tumor. The corticosterone secreted by the tumor. The corticosterone may well act directly on the hypothalamo-hypophyseal axis or it could act indirectly on the ovary; ovarian steroids would then exert a feedback effect. The ovary was atrophic and did not contain maturing Graafian follicles or corpora lutea. In somatotrophs, the number of secretory granules increased, probably reflecting suppression of hormonal release by corticosterone.