Immunohistochemical localization of activin A in human endometrial tissues during the menstrual cycle and in early pregnancy

Objective: To investigate the possible localization of activin A in human endometrial tissue. Methods: Human endometrial tissue was collected from 33 patients who were undergoing abdominal hysterectomy. Human decidual tissue was collected from 11 patients, who were having a therapeutic abortion. Tissue was fixed in Bouin's solution and made into paraffin sections. Tissue sections were stained with monoclonal antibodies against the inhibin/activin alpha- and beta A-subunits and activin A using an avidin-biotin-peroxidase complex technique. Results: No immunostaining with antibody against the alpha-subunit was observed in the human endometrium during the menstrual cycle or in the decidua during early pregnancy. By contrast, immunostaining for the beta A-subunit and activin A was observed in the cytoplasm of endometrial glands at all phases of the menstrual cycle and in the decidua during early pregnancy. The intensity of immunostaining for the beta A-subunit was strong during the menstrual phase, became weaker during the early proliferative phase, and was intense again at the late proliferative phase. The immunostaining for the beta A-subunit was weak during the early secretory phase and became very intense toward the midsecretory and late secretory phases. The intensity of immunostaining for activin A changed during the menstrual cycle and showed a tendency similar to that for beta A-subunit. The stromal tells were weakly immunoreactive with antibodies against the beta A-subunit and activin A from the menstrual to the midsecretory phase and became strong in the late secretory phase. Intense staining for the beta A-subunit and activin A was observed in the cytoplasm of decidual cells during early pregnancy. Conclusion: Activin A, but not inhibins, is localized in the endometrial tissue. The endometrium may be a major source of activin A during the normal menstrual cycle, and the decidua may be one of the sources of activin A. during early pregnancy. (C) 1998 by The American College of Obstetricians and Gynecologists.