The effect of sperm activation on pinopod formation in endometrial epithelium

Endometrial receptivity is crucial in implantation of the developing embryo in the endometrium and formation of the pregnancy. In this study, possible effect of sperm and uterine endometrial contact on formation of pinopod, an important element in morphological differentiation necessary for implantation, was investigated. In this experimental study, 42 female Spraque–Dawley albino rats and 14 male Spraque–Dawley albino rats (total 56 rats) were used. Vasectomy was performed in half of the male rats. For each group, two distinct branches were formed with 21 females and 7 males: Group 1 (non-vasectomized) and Group 2 (vasectomized). Cases were sacrificed and evaluated every day from Day 1 to Day 3. Scanning electron microscopic (SEM) images were analyzed according to different stages of pinopod development on different days. Pinopods were classified as developing, developed and regressing pinopod. The average number of pinopods were calculated by counting the pinopods at four endometrial regions examined for each rat and total number was divided by 4. Same procedure was done for all rats in every group. Results were compared among the groups. For statistical analysis among the groups, *Independent Samples Test (Mean ± Std) and **Mann Whitney U Test (Median (25–75%)) were used. The most important finding in SEM examination of uterus removed on the first day following mating from female rats that were copulated with non-vasectomy male rats which comprised the first group of the study was that heads of the sperms in the uterus were embedded in endometrial epithelium. Similarly, examination of the endometrium of uterus that were removed on postcoital second day revealed small number of developed pinopods (average 0.39) (P = 0.902). Examination was done by taking the developing pinopods within image area into account and number of developing pinopods in endometrium epithelium of the rats in first group (average 20.61) was higher than that of second group (average 12.86) (P < 0.001). Examination of endometrium of the uterus that were removed on third postcoital day revealed less number of developing pinopods in both groups. Examination of first group revealed an average of 1.21 developing pinopod, whereas the average number of developing pinopod in second group was 2.25 (P = 0.011). Examination based on the count of developed pinopods revealed that number of pinopods in first group (average 13.79) was higher than second group (average 8.96) (P < 0.001). Regressing pinopod images were observed in only endometrium that were taken on postcoital third day in the second group. In this study, it was clearly shown that sperms were entered into endometrial epithelium with their heads. It can be suggested that they might have a facilitating effect for pinopod formation by reacting with endometrial epithelium as a result of this invasion. It would be beneficial to demolish the other factors triggering pinopod formation to investigate whether presence of sperm alone in the uterus has an effect on pinopod formation.