Angiotensin-(1-7) in the Rabbit Ovary: A Novel Local Regulator of Ovulation.

Abstract

Several studies have shown the presence of the Renin-Angiotensin System (RAS) components in mammalian ovaries and their involvement in events such as follicular development, steroidogenesis, follicular atresia and ovulation. Recently, we have shown in the rat ovary the presence of a novel peptide of this system, the Angiotensin-(1-7). We have also shown the stimulatory effect of Ang-(1-7) on estradiol and progesterone production in ovaries of eCG pre-treated immature rats perfused in vitro. In the present study we determined the presence of Ang-(1-7) as well as of the MAS-receptor in the rabbit ovaries by immunohistochemistry (IHC). Furthermore, we evaluated the effect of Ang-(1-7) in the steroidogenesis and ovulation in rabbit ovary. IHC was carried out using Avidin-Biotin Peroxidase method, in slices of ovaries prefixed with Bouin. Ang-(1-7) and MAS immunoreactivity were observed in interstitial cells and oocytes. Immunoreactivity for Ang-(1-7) and MAS were observed also in theca and granulosa cells of preovulatory follicles in ovaries of eCG pretreated rabbits and in corpora lutea of mated rabbits. In order to verify the effect of Ang-(1-7) in the steroidogenesis and ovulation, immature female rabbits received eCG s.c. injection (50UI) 48h before the experiment. The ovaries of rabbits, anesthetized with Ketamina/Xilazina, were isolated and perfused during 10h in a closed circuit system with medium 199 containing BSA, heparin 0.2UI/ml, insulin 0.02UI/mL. Temperature (37°C), pH (7.4) and pressure are maintained constant. After a 1-hour stabilization period, the first sample of 1.8 mL was withdrawn and Ang-(1-7), A-779, hCG or combinations of them were added to the medium. The concentration of estradiol and progesterone were measured by radioimmunoassay. The oocytes present in the medium were counted using a reverse phase microscope. The ovulatory efficiency was determined by number of oocytes compared to the number of preovulatory follicles present in the ovary. Ang-(1-7) stimulated the estradiol and progesterone production and the effect was blocked by A-779, the specific Ang-(1-7) antagonist. Ang-(1-7) enhanced the ovulatory efficiency and the effect was antagonized by A-779. The ovulation induced by hCG was reduced by A-779, which seems to indicate the participation of endogenous Ang-(1-7) as a mediator of gonadotropins in the ovulatory process. Taken together these results show the involvement of a novel regulatory peptide in the ovulation. Financial Support: CAPES, CNPq, FAPEMIG. (poster)