Concentration of nitric oxide in uterine secretion from mares susceptible and resistant to chronic post-breeding endometritis

摘要

Post-breeding endometritis (PBE) is a physiological inflammation that serves to clear excess spermatozoa and contaminants from the uterus [1]. Mares are classified by their response to a uterine inflammation to be either susceptible or resistant to persistent endometritis [2,3]. Susceptible mares are often older, multiparous and fail to spontaneously clear their uteri from inflammatory products within 4 days [3,4]. In addition, they have a pendulous uterus suspended over the brim of the pelvis into the abdominal cavity. Although many facets of uterine defense mechanisms are involved, uterine contractions plays a key role in clearing inflammatory products from the uterus [1]. Both resistant and susceptible mares respond with increased myoelectrical activities during the first 6 h after breeding, but while the increased myoelectrical activity in resistant mares continued between 7 and 19 h, that of susceptible mares decreased to below baseline during this time [5]. The mechanism of impaired myoelectrical activity in susceptible mares is not known, but it coincides with the peak of PBE, which have been reported to occur around 12 h after breeding [6]. Nitric oxide (NO) is an inflammatory mediator that among other effects causes smooth muscle relaxation. It is synthesized by different cells (e.g. macrophages, neutrophils, epithelial and endothelial cells) from L-arginine by three isoforms of NO-synthases [7-10]. NO is synthesized in the mammalian uterus, causes uterine relaxation, and is influenced by steroid hormones [10-12]. We hypothesized that susceptible mares accumulate fluid and inflammatory products such as NO following breeding because of the pendulous position of the uterus. The objective of this experiment was to measure and compare the concentration of NO in uterine secretion collected from resistant and susceptible mares at 13 h after breeding.