Ultrastructure of the cell types of the anterior hypophysis in a lizard. III. Rostral gonadotrophs.

Abstract

Rostral gonadotrophs of the teiid lizard Cnemidopohorus lemniscatus are mainly situated in the rostral zone of the anterior hypophysis, but partially invade the caudal region when hyperactive. They are rounded or ovoid cells in which the dilated granular endoplasmic reticulum, containing a flocculent substance, forms large disseminated vesicles and, frequently, an expanded basal cisterna. Numerous free ribosomes lie in the hyaloplasm, and the Golgi apparatus has often a spherical arrangement. Secretory granules are round, homogeneous, of medium opacity, and closely bound by a membrane. They vary considerably in size, their largest diameters being four times greater than those of the smallest granules in most cells. Characteristic membrane-bound polymorphic bodies exist among the granules; they contain a filamentous substance and opaque or crystalline inclusions. The mitochondria are very elongated. Rostral gonadotrophs undergo marked variations throughout the year; in May they are voluminous, with vesicular nuclei, abundant secretory granules, large polymorphic bodies, conspicuous Golgi apparatuses and widely scattered vesicles of endoplasmic reticulum, whereas the small cells present in January show opposite features. Gonadectomy, in both sexes, produces activation of these cells, with progressive reduction in the number and size of secretory granules, until almost complete degranulation of many elements after sixty days. Metyrapone administration for eight days results in a striking regression of rostral gonadotrophs, which appear small, with shrunken nuclei, poorly developed organelles, and few, often large secretory granules.