Expression of NA/1 symporter (NIS) in endometrial mucosa of fertile, sterile and post-menopausal women

The expression of the Na/I Symporter (NIS) in the basolateral cell membrane of the thyroid follicular cells is responsible for the active accumulation of iodide within the thyroid gland and for the subsequent biosynthesis of thyroid hormones. However, several tissues, such as salivary glands, breast, stomach, colon, ovary and endometrium, express NIS even if they are unable to organify iodide. In order to investigate a possible role of NIS in the endometrium, we analyzed, by immunochemistry, the expression of NIS in 44 endometrial samples of 20 patients with primary unexplained infertility, 14 fertile women and 10 in postmenopausal. NIS immunostaining was detected in endometrial cells belonging to the majority of sterile, postmenopausal and fertile women. However, the sterile and post-menopausal patients showed a higher percentage of NIS reactive cells compared to the fertile women (60 +/- 21% and 57 +/- 18% vs 19 +/- 9%; p=0.0001). NIS immunostaining was localized on the membrane and cytoplasm of the endometrial cells. We could not find any correlation between endometrial thickness and NIS immunoexpression. Our results indicate that, in the absence of histological markers, a sterile endometrium can be recognized because of the high expressions of NIS. Moreover, NIS expressions, elevated in both sterile and menopause women, is not related to the estrogen levels, but it could be modulated by factors common to the two conditions. In conclusion, we speculate that NIS may play a role in the development of female sterility.