Localization of the renin-angiotensin system in the bovine ovary: Cyclic variation of the angiotensin II receptor expression

Angiotensin (Ang) II may modulate reproductive function in the bovine ovary . Therefore, expression and localization of a local ovarian renin-angiotens in system (RAS) were investigated by elucidating the influence of the estru s cycle, pregnancy, and the presence of follicular cysts. Receptor analysis and autoradiography were used to characterize and localize Ang II receptor s. Cyclic variations in the density of ovarian Ang II receptors were found with a higher value in estrus than in diestrus. The density in ovaries with follicular cysts was in the same order of magnitude as in estrus. The Ang II receptor type 2 (AT(2)) dominated in all three groups. Autoradiography s howed that the majority of antral follicles and follicular cysts had intens e AT(2) receptor binding in the theca externa. Binding was less intense in the theca interna, whereas there was no binding in the granulosa layer. In the corpora lutea, the AT(2) receptor was dominant in the capsule and in co nnective tissue infoldings, whereas no binding was observed in the luteal t issue. The type 1 Ang II receptor (AT(1)) was dominant in the stroma and sh owed no cyclic changes. Angiotensin-converting enzyme (ACE) activity was de tected in all aspirated follicular fluids and homogenates of ovarian tissue . Autoradiography showed that most of the ACE was localized on endothelial cells. Renin immunoreactivity was found in granulosa and thecal cells of an tral follicles and in luteal cells. Furthermore, solitary cells in the stro ma, presumably macrophages, displayed intense staining. Our finding of cycl ic changes support the concept of an active and regulated RAS in the bovine ovary.