Expression of adrenomedullin by human granulosa lutein cells and its effect on progesterone production.

Abstract

Adrenomedullin (AM) has diverse functions and is expressed in a variety of tissues. This study was conducted to investigate the expression of AM in the human ovary and its effect on progesterone production by human granulosa lutein cells. Follicular fluid and blood samples were obtained at the time of oocyte retrieval from patients undergoing in vitro-fertilization cycles. Concentrations of AM in follicular fluid and plasma were measured by RIA. Granulosa cells were isolated from follicular fluid and expression of AM mRNA was examined by RT-PCR. Granulosa lutein cells were cultured in vitro and secretion of AM by those cells was determined by immunoprecipitation followed by PAGE. Immunohistochemical staining with human ovaries was carried out, using a specific antibody to AM. Furthermore, the effect of AM on progesterone production by cultured granulosa lutein cells was studied. Concentrations of AM in follicular fluid collected just before ovulation were significantly higher than those in the plasma (P<0.01). AM mRNA was expressed in granulosa cells at the preovulatory stage. Cultured granulosa lutein cells secreted immunoreactive AM. With immunohistochemical staining, it was revealed that AM was most abundantly expressed in granulosa lutein cells at the midluteal phase. No appreciable staining for AM was observed in granulosa cells in primordial and preantral follicles, whereas immunolocalization of AM was noted in granulosa cells of dominant follicles although it was not as prominent as in granulosa lutein cells at the midluteal phase. Furthermore, addition of AM to cultured granulosa lutein cells augmented progesterone secretion in a dose-dependent manner. These results suggest that AM is transcribed and secreted in human granulosa lutein cells as a local factor to enhance progesterone production by those cells.