Evidence that the effect of angiotensin II on bovine oocyte nuclear maturation is mediated by prostaglandins E2 and F2α

Abstract

Angiotensin II (AngII) prevents the inhibitory effect of follicular cells on oocyte maturation, but its involvement in LH-induced meiotic resumption remains unknown. The aim of this study was to assess the involvement of AngII in LH-induced meiotic resumption and of prostaglandins (PGs) in the action of AngII. In the experiment I, seven cows were superovulated, intrafollicularly injected with 10 mM saralasin (a competitive AngII antagonist) or saline when the follicles reached a diameter larger than 12 mm, and challenged with a GnRH agonist to induce an LH surge. Fifteen hours after GnRH, the animals were ovariectomized and the oocytes were recovered to determine the stage of meiosis. The oocytes from follicles that received saline were in germinal vesicle (GV) breakdown (30.8%) or metaphase I (MI; 69.2%) stage while those that received saralasin were in the GV stage (100%; P!0.001) 15 h after GnRH agonist. In another experiment, oocytes were co-cultured with follicular hemisections for 15 h to determine whether PGs mediate the effect of AngII on meiotic resumption. Indomethacin (10 mM) inhibited AngII-induced meiotic resumption (13.4 vs 77.5% MI without indomethacin; P!0.001). Furthermore, the GV oocytes progressed to MI at a similar rate when PGE 2 , PGF 2a or AngII was present in the co-culture system with follicular cells (PGE 2 77.4%, PGF 2a 70.0%, and AngII 75.0% MI). In conclusion, our results provide strong evidence that AngII mediates the resumption of meiosis induced by an LH surge in bovine oocytes and that this event is dependent on PGE 2 or PGF 2a produced by follicular cells. Reproduction (2008) 136 733-740

Angiotensin II profile and mRNA encoding RAS proteins during bovine follicular wave

“…9 In contrast, the AT2 blocker inhibited ovulation and oocyte maturation. [10][11][12] It is suggested that in extra-renal tissues there are other enzymes that may be responsible for the production of AngII. 13,14 Husain et al 4 obtained AngII in vitro from angiotensinogen, using plasminogen activator as catalyst enzyme.…”

Methods to study ovarian function in monovulatory species using the cow as a model

“…In this regard, it is important to consider that GnRH induces a transitory increase in LH that lasts for 6 h whereas after porcine LH (pLH) injection its levels remain elevated for about 20 h (Behrouzi et al, 2016). If the research goal is to assess oocyte meiotic resumption, FSH can be used before GnRH or LH treatment to increase the number of follicles per cow (Barreta et al, 2008;Siqueira et al, 2012).…”

“…Superovulation followed by multiple intrafollicular injections and ovariectomy enables examination of factors involved in meiotic resumption after GnRH challenge (Barreta et al, 2008).…”

“…To facilitate the intrafollicular injection procedure and eliminate follicles non-responsive to LH (Sartori et al, 2001), all follicles with diameter between 5 to 11 mm are aspirated using a vacuum pump, leaving no more than the three largest follicles in each ovary (Siqueira et al, 2012). On the afternoon of the day of intrafollicular injection (day 10), the intravaginal progesterone device is removed, each ovary is examined by transrectal ultrasonography, and all follicles >12 mm in diameter are subjected to intrafollicular injections (Barreta et al, 2008). To confirm the success of the procedure, cows are evaluated 2 h after intrafollicular injection and follicles that have a reduction in diameter greater than 2 mm, suggesting follicular fluid leakage, are removed from the experiments.…”

“…Approximately 90% of oocytes recovered from saline injected follicles were at germinal vesicle breakdown (GVB) or metaphase I (MI) stages at 12 h after GnRH injection (Barreta et al, 2008;Siqueira et al, 2012). This confirmed that intrafollicular injection did not affect meiotic resumption.…”