Angiotensin II reverses the inhibitory action produced by theca cells on bovine oocyte nuclear maturation

The presence of prorenin, renin, angiotensinogen, angiotensin-converting enzyme, angiotensin II (Ang II) and Ang II receptors in the ovary is suggestive of a functional ovarian renin-angiotensin system (RAS). In cattle, the expression of Ang II is greatest in large follicles, suggesting that it is important during follicular growth and maturation. The present study was designed to investigate the role of Ang II in bovine oocyte nuclear maturation. Bovine cumulus-oocyte complexes (COCs) were cultured with or without follicular cells and Ang II or saralasin (Ang II antagonist). In the absence of follicular cells, Ang II at 0, 10−11, 10−9 and 10−7 M did not affect the percentage of oocytes reaching the germinal vesicle breakdown (GVBD), metaphase I (MI) and metaphase II (MII) stage after 7-h (41.3 ± 4.3, 35.3 ± 4.0, 31.3 ± 9.7, 38.7 ± 8.6), 12-h (31.6 ± 7.0, 34.7 ± 6.1, 31.7 ± 5.3, 28.9 ± 9.1; mean ± S.E.M.) and 18-h (44.9 ± 7.3, 58.4 ± 8.4, 53.1 ± 7.4, 44.9 ± 7.3) of culture, respectively. Similarly, saralasin at 0, 10−11, 10−9 and 10−7 M did not affect the percentage of oocytes reaching MII stage after 18-h of culture (37.6 ± 7.4, 34.4 ± 7.7, 30.0 ± 10.8 and 31.2 ± 5.1, respectively). The theca cells (MII = 22.9%) or medium conditioned with follicular cells (GV = 65.5%, MI = 23.6%) inhibited oocyte maturation; however, theca cells (MII = 35.5 ± 4.9; P < 0.05) or medium conditioned with follicular cells (GV = 34.6%, MI = 52.7%; P < 0.01) were not able to inhibit nuclear maturation when Ang II (10−11 M) was present in the culture system. Theca cells remained viable during the culture period when Ang II was present. Therefore, results supported the idea of a role of Ang II in blocking the inhibitory effect of theca cells on nuclear maturation of bovine oocytes.