Nitric oxide synthesis is increased in the endometrial tissue of women with endometriosis

Background: Previous studies have shown that peritoneal macrophages from women with endometriosis produce excess nitric oxide (NO). This study was designed to quantify the amount of NO and determine the expression of endothelial (eNOS) and inducible NO synthases (iNOS) in women with and without endometriosis. Methods: An enzyme-linked immunosorbent assay (ELISA) was performed on endometrial tissues obtained from controls (myoma, n = 30) and on eutopic/ectopic endometrial tissues from endometriosis patients (n = 34) to evaluate eNOS and iNOS protein concentrations in these endometrial tissues. A rapid-response chemiluminescence analyser was used to measure NO directly in fresh endometrial tissues. Results: Mean (± SEM) levels of NO were significantly increased in the endometrial tissues of women with endometriosis (13.2 ± 7.8 versus 19.8 ± 12.6 nmol/g tissue; P = 0.016). Apparently higher levels of NO were found in ectopic compared with eutopic endometrium (P = 0.057). Endometrial tissues of women with endometriosis appeared to contain more iNOS than those of controls (3.6 ± 2.2 versus 8.6 ± 12.2 pg/μg protein; P = 0.06), but no significant difference was found in eNOS levels. Conclusions: Greater amounts of NO and NOS are present in the endometrial tissues of women with endometriosis, implying a possible role for NO in the pathogenesis of endometriosis.