Nitric oxide levels and nitric oxide synthase expression in uterine samples from mares susceptible and resistant to persistent breeding-induced endometritis.

PROBLEM: Breeding-induced endometritis (BIE) in the mare is resolved by 36 hr after insemination in resistant mares. However, 10-15% susceptible broodmares fail to do so because of impaired uterine contractility between 7 and 19 hr after exposure to seminal or bacterial challenge, which reduces their fertility.

METHOD OF STUDY: Nitric oxide (NO) in uterine secretions, and expression of nitric oxide synthase (NOS) in uterine biopsies were compared between susceptible and resistant groups 13 hr after insemination.

RESULTS

Susceptible mares had a higher NO in their uterine secretions and greater inducible NOS (iNOS) expression in their biopsies compared with resistant mares.

CONCLUSIONS

The NO mediates smooth muscle relaxation, but its role in persistent BIE has not been determined. Our data suggests a possible role of NO, either directly or in a NO-associated pathway, in delayed uterine clearance.