Immunocytochemical Localization of Angiotensinogen and Angiotensin II in the Rat Pituitary

Abstract

The presence and distribution of angiotensinogen and angiotensin II (All) were demonstrated in rat pituitary by immunocytochemical staining with the avidin-biotin-peroxidase method, using primary polyclonal antibodies specific for angiotensinogen and All. Silver enhancement of the reaction product was used to intensify lightly stained areas. Attempts were made to identify immunopositive cells by colocalization studies with antisera against luteinizing hormone, prolactin and S-100, a glial cell protein. In the anterior pituitary, angiotensinogen-immunoreactivity was observed in cells lining follicle-like structures. These cells, which were irregularly shaped and had processes extending between the glandular cells, did not colocalize with any of the reference antisera and are therefore of unknown cell type. The follicular endothelium was also immunopositive for angiotensinogen. After silver intensification, dispersed immunoreactive glandular cells were consistently observed in the anterior lobe. A proportion of these costained for luteinizing hormone, but not prolactin or S-100, indicating their identity as gonadotrophs. In the posterior pituitary, angiotensinogen immunostaining was associated only with the vasculature, while groups of immunopositive cells were observed in the medial region of the intermediate lobe after silver enhancement. All-immunoreactivity was observed in large cells preferentially located a t the poles of the anterior pituitary which also costained for luteinizing hormone. No staining was observed in either the posterior or intermediate lobes. The presence of immunoreactive angiotensinogen in all three lobes of the pituitary suggests that there a r e sites, in addition to gonadotrophs, at which the intracellular production of All could occur.The octapeptide angiotensin IT (AII) regulates the release of several hormones from the anterior pituitary. In both in vivo and in vifro, A11 is a stimulus for the secretion of prolactin (PRL) (1-4), adrenocorticotrophin (ACTH) ( 5 , 6), luteinizing hormone (LH) (7) and P-endorphin (8). These effects may be mediated by specific A11 receptors located on pituitary cells (9-11) or A11 may function through intermediate releasing factors, such as corticotrophin-releasing factor, as is the case for AH-stimulated release of ACTH (1 2-1 5). Of interest is the possibility that the pituitary is synthesizing and secreting AII, as part of an endogenous reninangiotensin system (RAS), to directly alter pituitary function.Several observations support the idea of a functioning RAS in the pituitary: 1) the demonstration of renin (16-19) and converting enzyme in the pituitary (20-23); 2) the detection of renin mRNA in pituitary extracts (24); 3) the identification and HPLC characterization of A11 from the hypophysis (25, 26); 4) the colocalization, by immunocytochemistry, of both renin and A11 in the rat gonadotroph (19,27) or human lactotroph (28); and 5) the demonstration of specific A11 receptors in the pituitary (9-1 1). However, the existence of angiotensino...

Angiotensinogen, Prorenin, and Renin Are Co-localized in the Secretory Granules of All Glandular Cells of the Rat Anterior Pituitary: An Immunoultrastructural Study

“…Deschepper and Ganong (1991) and Ganong et al (1989) reported that AGT is located in a separate population of cells and does not co-localize with any known anterior pituitary hormone. By contrast, Sernia et al (1992Sernia et al ( ,1997 and Thomas and Sernia (1990) detected AGT in gonadotropes and also in a population of perisinusoidal cells. In the rat pituitary, RAS components, either AGT (Ganong et al 1989; Thomas and Sernia 1990;Deschepper and Ga-nong 1991;Sernia et al 1992) or renin (Naruse et al 1981(Naruse et al ,1986, were not detected in lactotropes.…”

“…By contrast, Sernia et al (1992Sernia et al ( ,1997 and Thomas and Sernia (1990) detected AGT in gonadotropes and also in a population of perisinusoidal cells. In the rat pituitary, RAS components, either AGT (Ganong et al 1989; Thomas and Sernia 1990;Deschepper and Ga-nong 1991;Sernia et al 1992) or renin (Naruse et al 1981(Naruse et al ,1986, were not detected in lactotropes. The presence of AII in lactotropes has been reported by some authors (Steele et al 1982).…”

“…Renin has not been detected in rat somatotropes (Naruse et al 1981;Saint-André et al 1989), corticotropes, or thyrotropes (Naruse et al 1981). RAS constituents were not found in folliculostellate cells, identified by their immunoreactivity to the S-100 protein (Ganong et al 1989;Thomas and Sernia 1990;Deschepper and Ganong 1991;Sernia et al 1992Sernia et al ,1997.…”

Angiotensin II AT1AReceptor mRNA Expression Is Induced by Estrogen–Progesterone in Dopaminergic Neurons of the Female Rat Arcuate Nucleus

“…In the anterior pituitary, Ang II is produced locally in gonadotrophs and acts in a paracrine manner on lactotrophs to stimulate prolactin release (Aguilera et al, 1982;Paglin et al, 1984;Ganong et al, 1989;Thomas and Sernia, 1990), an effect mediated by AT 1 receptors (Becú-Villalobos et al, 1994;Moreau et al, 1994). Estrogen treatment of OVX rats downregulates the number of AT 1 receptors in the anterior pituitary (Chen and Printz, 1983;Carriére et al, 1986;Seltzer et al, 1992).…”

“…In the anterior pituitary, Ang II is synthesized locally and stimulates prolactin release (Steele et al, 1981;Aguilera et al, 1982;Schramme and Denef, 1983;Ganong et al, 1989;Jones et al, 1990;Steele and Myers, 1990;Thomas and Sernia, 1990). Ang II also participates in brain mechanisms controlling pituitary prolactin release, but here its role is inhibitory rather than stimulatory Steele, 1989, 1991).…”