Prolactin receptor in human endometriotic tissues

Background. Augmented serum prolactin (PRL) levels have been implicated as a cause for infertility in patients with endometriosis. However, it has not been established whether this lactogenic hormone or its receptor (PRLR) have specific effects on the development of human endometriosis. In the present study we assessed PRLR expression in human endometriotic and normal tissue. Methods. Fourteen patients with laparoscopically proven endometriosis were recruited and the negative or positive expression of the PRLR in normal endometrial and endometriotic tissues obtained during the mid‐late proliferative phase of the menstrual cycle was evaluated by RT‐PCR. Evaluation of serum prolactin, and peritoneal fluid estradiol content were carried out by specific radioimmunoassays (RIA). Results. In endometriotic tissue samples the corresponding 1048 bp PRLR transcript was negative in 12/14 of the samples (86%) and positive in two samples (14%). The opposite was seen in normal tissue, since PRLR expression was positive in 11/14 samples (79%) and negative in the remaining three samples (21%). There was an association between serum prolactin concentrations and PRLR expression in normal tissue but not in endometriotic tissue. Conclusions. The PRLR is expressed in normal endometrium, while cells of the endometriotic tissues did not express the PRLR, at least during the mid‐late proliferative phase of the menstrual cycle. The absence of the PRLR in the endometriotic tissues could not be correlated with the serum prolactin levels. These results suggest the existence of differential regulation of PRLR expression between normal and endometriotic tissue.