Development of the vasculature of the anterior pituitary: Ontogeny of basic fibroblast growth factor

Abstract

This study correlates the ontogeny of basic fibroblast growth factor (FGF) with the development of the vasculature of the anterior pituitary (AP) in two strains of rat, Sprague-Dawley (SD) and Fischer 344 (F344). Immunolocalization of FGF was followed from the first appearance of Rathke's pouch (RP) in 12-day (12d) fetuses, through each day of fetal development, and in 5,20, and 50d postnatal female rats. In addition, the ontogeny of folliculo-stellate cells (FSC) is described, since previous studies suggested that these unique cells might function as phagocytes in the regulation of FGF. In both rat strains, vascularization of the A P commenced in 16d fetuses. In 15-20d fetuses, dense foci of immunopositivity for extracellular FGF were apparent at sites of capillary penetration adjacent to partially disrupted, immature gonadotropes. Localization of FGF was first detected in immature gonadotropes in 18d fetuses and persisted in the cytosol of a subpopulation of gonadotropes thereafter. In 15d fetuses, FGF was localized within the cytosol intimately associated with the peripheral-facing plasma membranes of all cells of the adenohypophysis, and persisted to variable degrees in later fetal stages. Localization of FGF within nuclei of AP parenchymal cells was evident only in 16-17d fetuses. Although the ontogeny of FGF and vascularization of the AP was very similar in both rat strains, the ontogeny of FSC differed markedly. In both strains, follicular lumens contained FGF during late fetal and early postnatal development. However, both electron microscopy and immunostaining for S-100 marker protein revealed that the postero-lateral edges of the A P of F344 rats often lacked FSC when compared to SD rats, a situation which could compromise regulation of FGF by FSC at the A P periphery in that strain, and thereby contribute to the neovascularization from systemic blood vessels known to occur in that strain during prolactinoma formation.

Immunohistochemical Localization of Basic Fibroblast Growth Factor and Gonadotrophin in the Goat Pituitary Gland.

“…However, bFGF was also demonstrated in the nuclei of parenchymal cells. Similar to our results in previous studies, bFGF was detected immunohistochemically in the nuclei of pituitary parenchymal cells in rats and humans [8,16]. In vitro studies [18,19] revealed that bFGF is first translated and located in the cytosol, and then translocates into and is accumulated in the nuclei.…”

“…Several hypotheses have been proposed concerning the physiological roles of bFGF in the pituitary gland. In rat fetuses [8], immunopositivity for extracellular bFGF was observed at sites of capillary penetration adjacent to immature gonadotrophs during the early stages of pregnancy, and then bFGF was detected in the cytosol of a subpopulation of gonadotrophs. bFGF stimulates angiogenesis and plays an important role in tumorigenesis of prolactinomas in rats [20].…”

“…We concluded that bFGF-positive parenchymal cells include a subpopulation of gonadotrophs and/or corticotrophs. In previous studies in rats [3,8], immunoreactivity for bFGF was also observed within the cytosol of both gonadotrophs and corticotrophs. However, Marín et al [16] demonstrated the presence of bFGF in somatotrophs in human pituitary glands.…”

“…Previous studies, indicating immunoreactivity for bFGF using a range of fixation and preparative protocols in rat kidney and human eye, suggested that the immunostaining patterns of bFGF are dependent on the immunohistochemical procedures [4,7]. Also immunohistochemical studies of rat pituitary glands have suggested that bFGF is present in a subpopulation of gonadotrophs and/or corticotrophs [3,8]. In the anterior pituitary glands of ruminants and other species, the zona tuberalis (ZT) is composed of basophils, e.g.…”

Genesis of Prolactinomas: Studies Using Estrogen-Treated Animals

“…At present, there is no answer as to why some humans and animals are more responsive to estrogen's actions. However, it is interesting to note that there are slight structural differences in the pituitaries of estrogensensitive Fischer-344 and estrogen-insensitive Sprague-Dawley rats, including a difference in the number of supporting folliculo-stellate cells [30]. The differences in folliculo-stellate cell numbers between these two strains could be significant in tumorigenesis because these cells are a major source of bFGF, which regulates lactotropic cell proliferation [31].…”