Prolactin is an autocrine or paracrine growth factor for human myometrial and leiomyoma cells

Objective: To test the hypothesis that prolactin (PRL) acts as a mitogenic growth factor for human leiomyoma and myometrial cells. Methods: To test th is hypothesis, we performed three different types of experiments. First, we assessed whether exogenous PRL acted as a mitogen for cu Itu red uterine s mooth muscle cells. Second, we examined the role of endogenous PRL by asses sing the cell number after exposure of the cultures to a neutralizing antib ody to PRL. Finally, we examined both fresh tissues and cultured cells for expression of the PRL receptor messenger ribonucleic acid using the techniq ues of reverse-transcriptase polymerase chain reaction and Southern blottin g. Results: A significant suppression in cell number was seen after 5 days of culture for leiomyoma cells but not for myometrial cells after treatment with exogenous PRL. Both cell types showed a significant decrease in cell number after treatment with anti-PRL antibody. A 893-bp segment consistent with the cytoplasmic domain of the long form of the PRL receptor was amplif ied from both fresh and cultured tissues and confirmed by Southern blotting and sequencing. Conclusions: PRL appears to be an autocrine or paracrine g rowth factor for both leiomyoma and myometrial cells. However, there are so me differences between tissues in their sensitivity to this growth factor.