The importance and potential role of inducible Nitric Oxide Synthase (iNOS) in the maturation of rat cervix

Cervical maturation is an inflammatory reaction which involves infiltration of leukocytes, changes in ECM component elements and restructuring of collagen fibers. Despite many mediators of this event having been known, the exact control mechanism is still largely unknown. The inflammatory mediator NO has been suggested to stimulate MMP activity and to suppress proteoglican synthesis in some other tissues. Therefore, we aimed to clarify the possible role of NO during pregnancy and cervical reconstruction at birth by using immunohistochemical techniques combined with TEM. In this study, we used 108 female Wistar rats which were 200-250g. Two males per one female were caged together overnight for copulation. The pregnancies were detected by vaginal smear and spermium positive females were accepted as pregnant as of day 0. Estrous day, pre-natal days 18, 20, 21 and post-natal day 0 animals were constituted of the control group. Pre-natal days 18, 20, 21 and post-natal day 0 animals were constituted of the experimental group. The experimental group were treated with orally given L-NAME for 5 days with a dose of 50mg/day/rat. The tissues from both control and experimental groups were taken from the desired days and processed for routine light microscope and transmission electron microscope examinations. One piece of each tissue were also stored for nitrite/nitrate measurements. The iNOS distribution were evaluated in paraffin cervix tissue sections. These sections were also used to detect the leukocyte density with CD45 immunohistochemistry. TEM sections were used to evaluate the cellular and structural changes. In L-NAME treated experimental group, dissolving of collagen fibers were also seen throughout the progression of pregnancy and at post-partum day 0. However, the staining intensity of iNOS and the nitrite/nitrate levels decreased more than in the control group. The number of CD45 positive leukocyte was increased with the progression of pregnancy and in post-partum 0 both in control and experimental groups compared to estrous.Our conclusions are as follows: 1) Because in L-NAME treated experimental group, the intensity of iNOS staining and the nitrite/nitrate levels were lower than the control group throughout the pregnancy, the NOS product NO might contribute to the cervical maturation and birth, 2) Because the treatment of L-NAME also resulted in birth, mediators other than NO might regulate this event, 3) Because the number of CD45 positive leukocytes seemed to be increased with the progression of pregnancy in both groups, we can tell the cervical maturation and birth events are inflammatory processes.