IMMUNOHISTOCHEMICAL LOCALIZATION OF INHIBIN SUBUNITS IN HUMAN CORPORA-LUTEA DURING MENSTRUAL-CYCLE AND PREGNANCY

The cellular localization of the alpha-, beta-A-, and beta-B-subunits of inhibin was studied in human corpora lutea (CL) during the menstrual cycle and pregnancy. Immunohistochemical techniques using antisera selective for each subunit were used to localize the polypeptide chains. Immunoreactive staining with antisera against the alpha-, beta-A-, and beta-B-subunits was mainly observed in granulosa luteal cells (luteal cells), whereas thecal luteal cells were faintly stained with antibodies selective for each inhibin subunit. The intensity of immunostaining with alpha-subunit antiserum in luteal cells increased from the early luteal phase to the midluteal phase and subsequently decreased toward the late luteal phase. Inhibin alpha-subunit in the retrogressive CL was not detected. Not only was the immunolocalization of both beta-A- and beta-B-subunits detected in the luteal cells of the CL of the cycle, but the relative intensity of immunostaining with beta-subunit antiserum changed in a pattern similar to that shown by the alpha-subunit. The luteal cells and thecal luteal cells in the CL of pregnancy exhibited positive staining with antisera directed against each inhibin subunit. The present findings provide further evidence that 1) immunoreactive inhibin subunits are present in luteal cells in the CL of the menstrual cycle; 2) the detectable level of each subunit changes in parallel with the function of the CL over the course of the menstrual cycle; and 3) the CL of pregnancy might be involved in serum inhibin elevation early in gestation.