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 at 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 are sites, in addition to gonadotrophs, at which the intracellular production of All could occur.