Endometrial expression and secretion of activin A, but not follistatin, increase in the secretory phase of the menstrual cycle

OBJECTIVE: Activin A is a growth factor expressed by human endometrium, and its biologic effects are counteracted by follistatin. We evaluate whether activin A and follistatin mRNA and peptide expression as well as protein secretion from human endometrium change throughout the menstrual cycle. METHODS: In 25 healthy fertile patients, uterine washing fluid was retrieved by hydrosonography. In a subgroup (n 13), endometrial tissue samples were collected by hysteroscopy during the proliferative (n 6) or secretory (n 7) phase of the menstrual cycle. Activin and follistatin mRNA and peptide expression were evaluated by reverse transcriptase-polymerase chain reaction (RT-PCR) and by immunohistochemistry (IHC), respectively. Activin A and follistatin levels were assayed in uterine washing fluids by specific enzyme-linked immunosorbent assays and evaluated according to the endometrial thickness and menstrual cycle days. RESULTS: Both activin A and follistatin mRNAs were expressed by human endometrium, and their peptides immunolocalized both in proliferative and secretory endometrial epithelial and stromal cells. A significant increase in immunoreactive activin A but not in follistatin was observed in glandular epithelium during the secretory phase. Activin A but not follistatin was significantly (P .0001) higher in the washing fluids collected during the secretory than proliferative phase of the menstrual cycle. In addition, a significant correlation was found between activin A, but not follistatin, and menstrual cycle days (P .0001) or endometrial thickness (P .0001). CONCLUSION: Both activin A and follistatin mRNAs are expressed by human endometrium; however, activin A but not follistatin peptide expression and secretion were increased in the secretory phase of the menstrual cycle, suggesting an important role in human endometrium