Distribution of mast cells in vaginal, cervical and uterine tissue of non-pregnant mares: investigations on correlations with ovarian steroids.

Mast cells constitute part of the cellular immune system of the genital tract. They play a potential role in cervical remodelling during parturition and are subject to the influence of ovarian steroids. In this study, the influence of oestradiol-17β and progesterone on the distribution of mast cells in equine vaginal, cervical and uterine tissue was evaluated. Genital tracts were retrieved from healthy mares at a local slaughterhouse. The cervix was divided along the longitudinal axis into five equivalent regions from cranial to caudal (R1 to R5). Toluidine blue staining was used for the detection of mast cells. Hormone values were determined via radioimmunoassay. In cervical tissue, mast cells were present at higher frequency and higher density than in vaginal and uterine tissue. Statistically significant differences were obtained between cervical R1 (cranial) and uterus as well as cervical R2 and uterus (p < 0.05). In cervical tissue, an association between the presence of mast cells and peripheral oestrogen concentrations was observed, whereas such correlation could not be established for vaginal and uterine tissue. With increasing oestradiol-17β concentrations, the density of mast cells in cervical tissue increased to a statistically significant degree in the cranial (r = 0.46; p = 0.05) and caudal (r = 0.5; p = 0.03) regions. We propose that mast cells play a role in the cyclic remodelling of the equine cervix during the course of the oestrous cycle. Elucidation of mechanisms controlling cervical remodelling could contribute to development of therapies for mares showing a lack in cervical opening during oestrus.