Evidence that angiotensin‐(1–7) is an intermediate of gonadotrophin‐induced oocyte maturation in the rat preovulatory follicle

Abstract

Several studies have shown the presence of components of the renin–angiotensin system in mammalian ovaries and their involvement in ovarian physiology. We have previously shown the presence of angiotensin‐(1–7) [Ang‐(1–7)], an important biologically active component of the renin–angiotensin system, and its receptor, Mas, in rat, rabbit and human ovaries. We have also shown the involvement of Ang‐(1–7) in the rabbit ovulatory process in vitro. In the present study, we observed that Ang‐(1–7) stimulated the resumption of meiosis in oocytes of rat preovulatory follicles, reaching more than 30% of oocytes with germinal vesicle breakdown. The specific antagonist of the Mas receptor, A‐779, inhibited the germinal vesicle breakdown induced by Ang‐(1–7) and reduced the oocyte maturation stimulated by luteinizing hormone (LH). Immunohistochemistry showed that LH increased both Ang‐(1–7) and angiotensin‐converting enzyme 2 (ACE2) staining in preovulatory follicles. The effect of gonadotrophins on mRNA expression of Mas and ACE2 in ovaries of immature equine chorionic gonadotrophin‐primed rats was analysed by real‐time PCR after 6 h of human chorionic gonadotrophin (hCG) injection, which exhibits LH‐like effects. After hCG treatment, ACE2 mRNA expression was higher in the ovaries of treated rats than in the ovaries of control rats, whereas Mas mRNA levels were unchanged. A‐779 changed the steroidogenesis stimulated by LH. An increased testosterone concentration and decreased progesterone levels were measured in the follicle medium. In conclusion, our results suggest that LH upregulates the ACE2–Ang‐(1–7)–Mas axis and that Ang‐(1–7) promotes meiotic resumption, possibly as a gonadotrophin intermediate.