[Morphological studies on estrogen-induced PRL cell hyperplasia in rat pituitary gland--immunocytochemical and...

It is well known that the tumorous lesion in rat anterior pituitary gland occurs after continuous administration of estrogen, which is mainly composed of PRL secreting cells. In this study the changes in rat PRL cells by estrogen treatment were studied histologically and immunocytochemically. Furthermore, intracellular structures in PRL cells were observed by high resolution scanning electron microscopy using the aldehyde prefix osmium-DMSO-osmium method. These rat pituitary tumors were established in Fischer-344 female rats by weekly injections of 2.5 mg estradiol valerate. The estrogen-induced, autonomous and transplantable rat pituitary tumors (MtT/F84) were also studied in the same manner and the findings were compared with estrogen-induced tumors. The increase of weight of pituitary gland and of serum PRL level correlated significantly with the number of estrogen administration. On the basis of histological findings, estrogen-induced pituitary tumors can be classified into two different stages, that is, hypertrophic hyperplasia and adenomatous hyperplasia. The former corresponds to the period until 6 weeks after the beginning of estrogen treatment and the latter to the period thereafter. In the former, PRL cells were significantly increased in number and volume, and were diffusely immunoreactive for PRL in the cytoplasm. Cell atypism was rarely found. The extent of acidophil staining was well preserved in hematoxylin-eosin staining. Ultrastructurally, organelles were well developed, especially rough endoplasmic reticulum showed whorl formation. Immature, irregularly shaped secretory granules were frequently observed within the Golgi area. Mature granules were richly stored at the periphery of the cell.(ABSTRACT TRUNCATED AT 250 WORDS)