Factors associated with patency of the uterine cervix in bitches with pyometra

This study examined factors involved in the patency of uterine cervices in the bitch with pyometra. The uterine cervices were obtained from the bitches with pyometra at the time of ovariohysterectomy. Cervical patency was measured by inserting the stainless steel rods with different diameter into cervical canals. Collagen concentration and collagenase activity (for type I collagen) in the tissue were determined and the number of neutrophils, which contain the enzymes related to collagen metabolism, and morphological changes in collagenous fibers were studied by histological examination. Levels of mRNA expressions for hormonal factors, estrogen receptor-α (ER-α), progesterone receptor (PR), relaxin (Rlx) and an attractant of neutrophils, interleukin-8 (IL-8), were determined by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). In the statistical analysis, the cervical patency positively correlated with the collagenase activity, and negative correlation was found between the cervical patency and collagen concentration. Histological examination indicated distinct positive correlation between the cervical patency and the number of neutrophils in the cervical stroma and that the collagenous fiber in the uterine cervix became thinner and degraded with increase of the cervical patency. Although there was no relationship between the cervical patency and the level of mRNA for ER-α, PR or Rlx, IL-8 mRNA level has significant positive correlation with the cervical patency and the number of neutrophils in the cervical stroma. These results suggest that the increased number of neutrophils in the uterine cervix, which could be related to the local expression of IL-8, may be involved in collagen degradation and connective tissue remodeling to increase cervical patency in the bitch with pyometra.