Association between elevated prolactin levels and circulating erythroid precursors in dialyzed patients

The prolactin (PRL) receptor (R), a member of the cytokine hemopoietin rece ptor superfamily, has been shown to activate early differentiation steps al ong the erythroid pathway. In particular PRL, a product of bone marrow stro ma, induces functional erythropoietin (EPO)-R on CD34(+) hemopoietic progen itors. In this study, expression of EPO-R mRNA and responsiveness to EPO we re assessed on enriched hemopoietic progenitor cells (HPC) from seven hyper prolactinemic and three normoprolactinemic patients and two normal subjects . Expression of EPO-R mRNA by semiquantitative reverse transcriptase-polyme rase chain reaction (RT-PCR) was found in HPC of four out of seven hyperpro lactinemic patients but not in normoprolactinemic patients or normal donors . Development of EPO-dependent Colony Forming Unit-Erythroid (CFU-E) coloni es in semi-solid medium was observed only in hyperprolactinemic patients (s ix out of seven). A much higher number of CFU-E colonies was observed in th e four patients with a positive EPO-R message. We conclude from these data that abnormally high levels of PRL may increase the number of EPO-responsiv e hemopoietic precursors in vivo as they do in vitro. Since hyperprolactine mia associates in these patients with depressed EPO production, it may be r egarded as a compensatory mechanism for the reduced availability of the hem opoietic factor.