Abstract

There is the strong evidence that follicle maturation and ovulation are closely related with hemodynamics and hence vascular activity. The aim of this study was to investigate the mRNA expression for the members of angiotensin and endothelin systems in bovine mature follicles before and after GnRH application and shortly after ovulation. The ovaries were collected by transvaginal ovariectomy (n=5 cows/group) and the follicles were classified into 5 groups: before LH surge; 3–5h after GnRH application (during LH surge); 10h after GnRH; 20h after GnRH; 25h after GnRH (peri-ovulation) and early corpus luteum (CL, d 1–3). For better characterization of follicle classes, prostaglandin (PG)F2alpha and PGE2 were determined by EIA in follicular fluid (FF). The concentration of PGF2alpha and PGE2 in FF increased at 20h after GnRH and showed the maximal level in the follicles just before ovulation. For the angiotensin system, the mRNA expression of angiotensin converting enzyme (ACE) and angiotensin type1 receptor (AT1R) in follicle tissue (theca plus granulosa layers) significantly decreased in follicles after GnRH application, but AT2R mRNA expression remained unchanged. Contrary to ACE mRNA expression, Ang II peptide concentrations in FF increased continuously after GnRH application to the maximum level in follicles just before ovulation. For the endothelin system, the mRNA expression of endothelin converting enzyme-1 (ECE-1), and ET receptors (ETR-A and ETR-B) in follicle tissue decreased after GnRH with further decrease before ovulation (25h after GnRH), while the endothelin-1 (ET-1) mRNA expression remained unchanged. The data strongly support the idea that Ang II is induced by LH surge and this vasoactive peptide is a potential stimulator of PG synthesis in the bovine preovulatory follicle.

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