Expressão de receptores de angiotensina II no desenvolvimento folicular e participação na regulação da maturação de oócitos bovinos

Abstract

This study was designed to investigate the role played by AngII receptors (AT1 and AT2) in follicle development and maturation of bovine oocytes. Receptor expression was assessed by the RT-PCR technique using preantral (secondary), 3-8, 6-7, and 12mm follicles. Secondary preantral follicles did not express AngII receptors. Antral follicles expressed AngII receptors distinctly. AT1 receptors were expressed in teca (TC) and granulose cells (GC) from follicles greater than 6mm. AT2 receptors were expressed in TC and GC from follicles >6mm. AT2 receptors were expressed in TC in follicles >3mm. Only follicles >12mm expressed AT2 receptors in GC. The investigation of oocyte maturation was evaluated in cumulus-oocyte complexes (COCs) from 2-8mm follicles obtained in slaughterhouses. The treatments were carried out using the co-culture of 20 COCs with 8 follicle hemi-sections for 12h in 20μL TCM199 plus 1mg/mL polyvinyl alcohol (negative control group: CON(-)), supplemented with AngII (AngII group), with AngII plus Losartan (LOS group), and with AngII plus PD123319 (PD123319 group). For the positive control group (CON(+)), COCs were cultured without follicle hemi-sections. Oocytes were analyzed for maturation stage in germinal vesicle (GV), germinal vesicle breakdown (GVB), and metaphase I (MI). The oocyte rate kept in GV observed in the groups cultured with receptor inhibitors AT1 (LOS: 65.5%, 78/119) and AT2 (PD123319: 54.6%, 53/97) was greater (p<0.05) than that of CON(+) (10.8%, 12/111) and AngII (22.7%, 25/110) groups, but no difference was seen as compared with CON(-) (50%, 53/106). In the MI analysis, the oocyte percentage that reached this stage in groups CON(+) and AngII (62.1%, 69/111 and 52.2%, 58/111, respectively) was greater (p<0.05) than that seen for CON(-), LOS and PD123319 (13.2%, 14/106; 0.8%, 1/119; 1.03%, 1/97, respectively). TC and GC expressed AngII receptors (AT1 and/or AT2) before antrum formation, according to follicle size. Both AT1 and AT2 receptors take part in the resumption and progression of meiosis in bovine oocytes.