Changes in basic fibroblast growth factor coincident with estradiol-induced hyperplasia of the anterior pituitaries of Fischer 344 and Sprague-Dawley rats.

Adult female Fischer 344 (F344) and Sprague-Dawley (SD) rats were treated with estradiol via Silastic implants for 10 and 20 days. This treatment period in F344 rats is sufficient to produce dramatic hyperplasia of anterior pituitary lactotropes, activation of folliculo-stellate cells (FS) as phagocytes, and reorganization of the blood supply, i.e. hemorrhagic lakes and arteriogenesis from vessels in the adjacent meninges. Estradiol-treated SD rats do not demonstrate a comparable response. We now report intense focal concentrations of cells immunopositive for basic fibroblast growth factor (FGF) in estradiol-treated F344 rats predominantly near the posterolateral edge of the anterior pituitary, a zone rich in gonadotropes and lactotropes. Immunostaining for FGF, by both light and electron microscopy, revealed that the immunopositive cells were gonadotropes, and that the immunoprecipitate was cytosolic and was most abundant in the cytosol facing the capillaries. Immunostaining for extracellular matrix-associated FGF also revealed foci of positivity at the postero-lateral edge. Estradiol-treated SD rats did not reveal comparable localization for FGF. Morphological analysis and immunolocalization of S-100 protein, a marker for FS cells, revealed that the periphery of the anterior pituitary of estradiol-treated F344 rats included numerous disrupted gonadotropes and, furthermore, was largely devoid of FS cells. This zone was more intact in control F344 rats, but lacked FS cells. The peripheral parenchyma of control and estradiol-treated SD rats was intact compared to that of F344 rats and consistently included FS cells. These results suggest that disruptions of gonadotropes at the pituitary periphery may release FGF, which could then stimulate angiogenesis from blood vessels within the adjacent meninges. The resultant systemic blood supply would stimulate lactotrope hypertrophy and hyperplasia. Since FS cells are known phagocytes within the anterior pituitary, their absence from the periphery of F344 rats may intensify or prolong the effect of the peripherally released FGF.