Immunolocalization of sex hormone-binding globulin (SHBG) in human ovarian follicles and corpus luteum

Sex hormone-binding globulin (SHBG), a hepatic carrier protein for sex steroids is expressed in different steroid-sensitive tissues, including Sertoli cells of the testis. It has been suggested that this protein may be one of the local regulators of spermatogenesis. The expression of SHBG in the ovary is currently unknown. We have previously demonstrated the synthesis of SHBG in granulosa-lutein cells from patients undergoing in vitro fertilization. In this study, the presence of SHBG in human ovarian follicles and corpora lutea is investigated, using immunohistochemistry on adult and fetal ovarian tissue sections. SHBG is localized in the whole granulosa layer at all stages of folliculogenesis, whereas, only isolated theca cells are immunostained. In primordial and primary follicles, the oocyte cytoplasm shows an intense immunostaining, which disappears after the secondary stage. In the microenvironment of the mature oocytes, SHBG is present in the surrounding cumulus cells, the perivitelline space, and nearby the oolemma. In the corpus luteum, SHBG is localized in large luteal cells, whereas, small luteal cells do not show any significant staining. By analogy with the testis, these results raise the question of an involvement of SHBG in the regulation of follicular maturation as well as in luteal function.