Effect of ovarian hormones on promotion of bactericidal activity by uterine secretions of ovariectomized mares.

The research conducted a study on horses that were ovariectomized to examine the effect of ovarian hormones on the bactericidal action of uterine secretions. It was found that while estrogen-related hormones showed an increase in bactericidal activity over time, the introduction of progesterone resulted in a consistent low bactericidal activity even after a significant period.

Objective of the Study and Method

• This study aimed to investigate the influence of ovarian hormones on the bactericidal and phagocytic activities of blood neutrophils in the uterine secretions of ovariectomized mares.
• The subjects of the study were mares that were given either oestradiol benzoate, progesterone, or an oily vehicle.
• Endometritis was induced in each subject via intrauterine infusion of glycogen, followed by the sequential collection of uterine washings up to 144 hours.

Findings and Interpretations

• The study found no significant difference in the speed of neutrophil mobilization into the uterus within the first 6 hours post-infusion between the three groups.
• There were significantly more uterine luminal neutrophils in the progesterone-treated horses than those treated with oestradiol by 24 hours post-infusion.
• Bactericidal activity was severely limited in the uterine washings from progesterone-treated mares, compared to oestradiol-treated and control mares.
• In estrogen-treated and control mares, bactericidal activity had increased by 144 hours, but it remained low in progesterone-treated mares.
• The ability of washings to opsonize yeast blastospores was not affected by either the treatment type or time.
• Increased levels of progesterone in the plasma were associated with decreased bactericidal activity of neutrophils in uterine washings, but the production of C3b, an integral part of the immune response, was not affected by hormone treatment.

Conclusion

• The results of this study suggest that the presence of ovarian hormones, particularly progesterone, can potentially suppress the bactericidal activity of the uterine secretions.
• While the exact effect of these hormones on the immune response remains uncertain, the significant reduction in the bactericidal activity can potentially increase the risk of infections in the uterus.