Angiopoietins Are Expressed in the Normal Rat Pituitary Gland

Abstract

Interaction of vascular endothelial growth factor (VEGF) with the angiopoietins (Ang) is an essential component of angiogenesis. Localization of VEGF in the anterior pituitary raises the possibility that Ang must be present in the pituitary gland as well. In this study Ang expression was detected in the normal rat pituitary gland at the gene level by reverse-transcriptase polymerase chain reaction and at the protein level by immunohistochemistry. The latter was analyzed by both light and confocal microscopy. Constitutive expression of Ang1, Ang2, and their receptor Tie2 was detected at both the mRNA and protein level in all the pituitary glands studied. Of interest was the localization of both Ang1 and Ang2 in scattered PAS positive adenohypophysial cells rather than in endothelial cells. Confocal microscopy showed colocalization of both Ang1 and Ang2 proteins within the same adenohypophysial cells. Dual immunostaining for Ang1 and the anterior pituitary hormones that show PAS positivity demonstrated colocalization of Ang1 with follicle stimulating hormone and luteinizing hormone. In the posterior pituitary, strong Ang1 signal observed in vascular endothelial cells masked the weak Ang2 signal, a pattern that is similar to that reported in brain endothelial cells. The presence of both angiopoietins and VEGF in the pituitary gland suggest that these ligands interact during angiogenesis as they are known to do in other systems to maintain the rich vascular network of the gland. This first report of angiopoietin localization in the rat pituitary gland opens a new line of investigation on angiogenesis in pituitary glands that will impact human endocrinology in the future.

Paracrinicity: The Story of 30 Years of Cellular Pituitary Crosstalk

“…Ang-1 promotes endothelial cell survival (protection from apoptosis) through the Akt pathway and stimulates endothelial cell migration, sprouting and tube formation. The cells that produce Ang-1 and Ang-2 in the anterior pituitary are the gonadotrophs, which is in striking contrast with the neural lobe where strong expression is seen in endothelial cells ( 816 ). It is remarkable that, in addition to angiopoietins, gonadotrophs produce FGF-2 and VEGF, which may be relevant to the neovascularisation from meningeal vessels into the postero-lateral zone of the anterior pituitary, known to be rich in gonadotrophs and lactotrophs (see earlier in this section).…”

Analysis of differential gene expression by fiber-optic BeadArray and pathway in prolactinomas

“…Nag et al [22] reported the localization of both Ang-1 and Ang-2 in scattered PAS positive adenohypophysial cells rather than in endothelial cells. There is also accumulating evidence that implicates Ang-2 in tumor progression [23].…”

Analysis of differential gene expression by bead-based fiber-optic array in growth-hormone-secreting pituitary adenomas

“…nag et al (18) reported that the localization of both anG-1 and anG-2 occurs in scattered periodic acid-Schiff (paS)-positive adenohypophysial cells rather than in endothelial cells. accumulated evidence also indicates that the production of anG-2 is implicated in tumor progression (19).…”