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 betaA 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).
CONCLUSIONS: 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.