An investigation of uterine nitric oxide production in mares susceptible and resistant to persistent breeding-induced endometritis and the effects of immunomodulation.

The research explores how uterine nitric oxide (NO) production varies in mares susceptible and resistant to persistent breeding-induced endometritis (PBIE), and the effects of certain treatments on this production. The results indicate a differential response to breeding in terms of NO production and expression of inducible NO synthase (iNOS) in resistant and susceptible mares, and the treatments dexamethasone or mycobacterial cell wall extract (MCWE) had varying effects.

Objective and Methodology

• The researchers’ primary goal was to examine the levels of intrauterine nitric oxide (NO) and endometrial inducible NO synthase (iNOS) in mares, either susceptible or resistant to persistent breeding-induced endometritis (PBIE) within 24 hours of mating.
• 12 mares, half susceptible and half resistant to PBIE, were assessed for uterine secretions and endometrial biopsies collected at different intervals following insemination.
• The collected materials were examined: uterine secretions for NO and biopsies for iNOS expression.
• A follow-up experiment involved treating six susceptible mares with either dexamethasone or MCWE before insemination. The mares’ uterine biopsies and secretions were then evaluated for NO and iNOS mRNA.

Findings and Interpretation

• The study’s results highlighted differences in NO and iNOS expression between mares resilient and susceptible to PBIE post-breeding.
• Resistant mares displayed an upsurge in iNOS mRNA expression as early as 2 hours following breeding compared to pre-breeding baseline, and this expression was notably higher than documented 12 and 24 hours after mating.
• Meanwhile, in susceptible mares, iNOS expression peaked 2 hours post-breeding, significantly higher than the 6-hour measure.
• The research also observed varying patterns between the two mare groups in terms of intrauterine NO: resistant mares had a steady amount over 24 hours, while susceptible mares showed an increase over time. Susceptible mares also recorded significantly higher cumulative NO than resistant mares at the 6 and 12-hour post-breeding measurements.
• The second experiment with treatments showed no observable changes in iNOS mRNA expression, but susceptible mares had higher NO compared to resistant mares, and the MCWE treatment reduced NO levels.

Conclusion and Implication

• The research showed that a mare’s susceptibility or resistance to PBIE affects the intrauterine NO and iNOS production following breeding, potentially shaping their reproductive processes and outcomes.
• Moreover, treatments with dexamethasone or MCWE can alter this NO production, providing a potential avenue for targeted interventions to combat PBIE.