Concentrations of arachidonate metabolites, steroids and histamine in preovulatory horse follicles after administration of human chorionic gonadotrophin and the effect of intrafollicular injection of indomethacin.

The research article presents a study on the hormonal changes in preovulatory follicles in mares (female horses), particularly focusing on progesterone and prostaglandins, after administering human chorionic gonadotrophin (hCG). The study also explores how blocking these hormonal processes with indomethacin may affect ovulation.

Research Objectives and Methodology

• This study aims to understand the hormonal changes occurring within preovulatory follicles in mares upon administering human chorionic gonadotrophin (hCG).
• Mares were administered with 2500 IU hCG intravenously when a preovulatory follicle of 35 mm in diameter was detected.
• Follicular fluid was extracted and analyzed at different intervals before and after the hCG administration (0h, 12h, 24h and 36h), looking for concentrations of various hormones such as progesterone, prostaglandin (PG) E2, PGF, 6-keto-PGF1 alpha, and thromboxane B2.
• Further, by injecting buffered saline or indomethacin (at different concentrations) into the follicles, the research attempted to discern whether blocking intrafollicular prostaglandin synthesis can influence ovulation.

Results and Findings

• The study found that there was a significant increase in the concentration of progesterone, PG E2, PG F, 6-keto-PGF1 alpha, and thromboxane B2 in follicular fluid between 0 and 36 hours after hCG injection.
• By the 36-hour mark, PGE2 was found in the highest concentrations, followed by PGF and 6-keto-PGF1 alpha. Thromboxane B2 was present but in lower concentrations than the other prostanoids.
• The concentration of 13,14-dihydro-15-keto-PGF2 alpha also saw a statistically significant increase between the 24- and 36-hour mark.
• Leukotriene B4, Leukotriene C4, and histamine were consistently present in the follicular fluid throughout all sampling periods and saw no significant changes over time.
• The second experiment suggested that blocking intrafollicular prostaglandin synthesis with indomethacin may delay luteinization, and induce lower plasma progesterone concentrations in the initial 5 days after injection.

Conclusion

• The results suggest a significant rise in intrafollicular concentrations of prostaglandins prior to ovulation in mares, indicating they may play an important role in the ovulation process.
• Blocking the intrafollicular prostaglandin synthesis appears to affect the ovulatory process, widening the interval between the injections and observation of luteinization, and causing lower plasma progesterone concentrations in mares.