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

This research paper investigates the concentrations of nitric oxide in the preovulatory follicles of mares before and after the administration of human chorionic gonadotropin (hCG). The study revealed that nitric oxide levels and progesterone concentrations increased while estradiol levels decreased following the administration of hCG. This provides evidence of an upregulated nitric oxide-generating system in the equine preovulatory follicle after hCG administration.

Investigation on Nitric Oxide Concentrations

• The researchers analyzed the follicular fluids of estrous mares. They used a control group treated with a saline solution and another group treated with nitric oxide synthase (NOS) inhibitors.
• The fluids were examined for nitric oxide (NO), estradiol-17beta (E2) and progesterone (P4) concentrations before and 36 hours after the administration of hCG.
• The results showed that control mares had lower nitric oxide concentrations in follicular fluids obtained before hCG administration than those obtained 36 hours after. This increase in nitric oxide signals that an NO-generating system in the equine preovulatory follicle is possibly upregulated with the administration of hCG.

Observations on Estradiol and Progesterone Levels

• Similar to nitric oxide, progesterone levels increased in control mares following the administration of hCG.
• On the contrary, estradiol levels of control follicles sampled before hCG administration were higher than those sampled 36 hours post-hCG administration.

Effects of Nitric Oxide Synthase (NOS) Inhibitors

• The study also analyzed the effects of NOS inhibitors, N(omega)-nitro-L-arginine methyl ester (L-NAME) and aminoguanidine (AG) on nitric oxide and progesterone concentrations, as well as on estradiol levels.
• It was found that mares treated with NOS inhibitors had lower intrafollicular concentrations of nitric oxide and progesterone, both before and after hCG administration.
• In addition, unlike control mares, estradiol concentrations in follicles of mares treated with NOS inhibitors did not decrease after hCG administration.