Concentrations of nitric oxide in equine preovulatory follicles before and after administration of human chorionic gonadotropin

Abstract

In the present study, follicular fluids of estrous mares treated with saline solution (Control) or nitric oxide synthase (NOS) inhibitors were analyzed for nitric oxide (NO), estradiol-17β (E 2) and progesterone (P 4) concentrations before and 36 h after administration of human chorionic gonadotropin (hCG). Follicular fluids obtained before (0 h) hCG administration from control mares had lower concentrations of NO than those obtained 36 h after administration of hCG (58.3±17.8 μmol versus 340.4±57.7 μmol; P<0.05). A similar pattern was also noted for intrafollicular P 4 in control mares, which had lower concentrations of intrafollicular P 4 before hCG than 36 h post-hCG administration ( P<0.05). As expected, E 2 concentrations of control follicles sampled before hCG administration were higher than those sampled 36 h post-hCG administration ( P<0.05). However, the E 2 concentrations in follicles of mares treated with the NOS inhibitors N ω-nitro- l-arginine methyl ester ( l-NAME) or aminoguanidine (AG) did not decrease after hCG administration, unlike those in control mares ( P>0.10). In addition, mares treated with NOS inhibitors had lower intrafollicular concentrations of NO and P 4 than control mares, both before and after hCG administration ( P<0.05). Increased intrafollicular concentrations of NO in control, hCG-stimulated mares provide evidence for the presence of an NO-generating system in the equine preovulatory follicle that is likely upregulated following administration of hCG.