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

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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 (E2) and progesterone (P4) 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 ofhCG (58.3 ± 17.8 μmol versus 340.4 ± 57.7 μmol; P < 0.05). A similar pattern was also noted for intrafollicular P4 in control mares, which had lower concentrations of intrafollicular P4 before hCG than 36 h post-hCG administration (P < 0.05). As expected, E2 concentrations of control follicles sampled before hCG administration were higher than those sampled 36 h post-hCG administration (P < 0.05). However, the E2 concentrations in follicles of mares treated with the NOS inhibitors Nω-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 P4 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. © 2003 Elsevier Science Inc. All rights reserved.

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