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      To investigate the expression of melatonin receptors (MR1A and MR1B) in human endometrium and endometriotic tissues.


      Study participants included women (n=31) with a confirmed diagnosis of endometriosis (endometrioma n=20 and peritoneal lesions n=11). The control group were women with pelvic pain but no evidence of endometriosis (n=15). Eutopic and ectopic endometrial tissue was collected. Melatonin receptors were localized by immunohistochemistry and expression (mRNA and protein) was quantified in tissue samples. RL95-2 cells, a human endometrial epithelial cell line, were used to assess effects of increasing concentrations of melatonin (1.0nM – 1.0 ?M) ± estradiol (1.0 nM) on cell proliferation. Significant differences were determined by one-way ANOVA.


      MR1A and MR1B were localized to glandular epithelial cells and were expressed in eutopic and ectopic endometrial tissue. Expression of both receptors was significantly greater in peritoneal lesions compared to endometriomas and eutopic endometrium. However, protein expression of MR1A was significantly lower in peritoneal lesions compared to eutopic endometrium whilst MR1B expression was not significantly different between groups. Melatonin treatment attenuated estradiol-induced cell proliferation beginning at the 1.0nM concentration.


      Melatonin receptors are expressed in human endometrial tissue, with differential expression between different endometrial tissue samples. Different patterns seen in gene and protein expression warrants further investigation. Melatonin may represent a novel non-hormonal adjuvant for the treatment of endometriosis.

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