Cyclooxygenase-2 is inhibited in prolonged luteal maintenance induced by intrauterine devices in mares.

The research article presents findings on the potential mechanism by which intrauterine devices (IUDs) may cause prolonged luteal phases in mares, focusing on the possible role of cyclooxygenase-2 (COX-2) in this process.

Objective and Methodology

• The study aimed at investigating how IUDs affect the uterus of mares to result in prolonged luteal phases, with a focus on the role of COX-2 in maintaining the corpus luteum (CL).
• A total of 27 healthy mares were used in the study, where 12 were inseminated (AI), and 15 were fitted with IUDs.
• The researchers took blood samples on various days for progesterone analysis. These days were relative to the day of ovulation.
• The horses were further classified into four groups using ultrasound examinations and serum progesterone concentrations on Days 14 and 15: non-pregnant (AI-N), pregnant (AI-P), normal (IUD-N), and prolonged luteal phase (IUD-P).
• Also, blood sampling to quantify the PGF metabolite (PGFM) was carried out at hourly intervals on Day 14 and over a 7-hour period on Day 15.
• On Day 15, a low-volume uterine lavage followed by an endometrial biopsy was done.
• Estradiol concentration in the Day 15 serum and lavage fluid was determined, and the abundance of COX-2 was evaluated in the biopsy specimens using western blotting (WB) and immunohistochemistry (IHC).

Findings

• All pregnant mares tested negative for COX-2 in IHC samples, and 5 out of 8 were also negative in WB samples. This indicates the absence or low levels of COX-2 in these mares.
• All mares in the IUD-N group tested positive for COX-2, showing the presence of COX-2 in these horses.
• In the IUD-P group, five out of seven mares were negative for COX-2 with the IHC samples and four were negative with the WB samples. These findings suggest that in mares with a prolonged luteal phase (IUD-P), IUDs likely lead to the suppression of COX-2.

Conclusion

• The findings suggest that IUDs, when effective, appear to suppress COX-2, resulting in the inhibition of PGF2α release and thus leading to maintenance of the corpus luteum.
• This possible mechanism could explain the observed prolongation of the luteal phase in mares fitted with IUDs.