Prolactin receptor gene expression and immunolocalization of the prolactin receptor in human luteinized granulosa cells

Prolactin is mainly known for its role in breast development and lactation, but has been also implicated in other physiological functions such as immunoregulation and ovarian steroid production. Although prolactin and prolactin receptor (PRL-R) transcripts have been previously identified in the human ovary, the spatial localization of the receptor is unknown. To investigate the presence of PRL-R within the follicular apparatus, human luteinized granulosa cells were obtained at the time of follicular aspiration from women undergoing ovarian stimulation for IVF. RNA extracted from these cells was subjected to reverse transcriptase-polymerase chain reaction (RT-PCR) using specific primers for the PRL-R gene. In addition, paraffin sections of isolated granulosa cells and sections of premenopausal human ovaries were immunostained with a mouse anti-human PRL-R monoclonal antibody. PRL-R were immunolocalized to the cell membrane of isolated luteinized granulosa cells and PRL-R transcripts were detected in the extracted RNA. No detectable staining was noted in secondary and early antral follicles in archived paraffin sections. These findings confirm the presence of PRL-R in human luteinized granulosa cells and suggest a localized role for PRL within the mature follicle. The absence of PRL-R in the early follicle suggests that the effects of prolactin are exerted around the time of ovulation.