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 this hypothesis, we performed three different types of experiments. First, we assessed whether exogenous PRL acted as a mitogen for cultured uterine smooth muscle cells. Second, we examined the role of endogenous PRL by assessing the cell number after exposure of the cultures to a neutralizing antibody to PRL. Finally, we examined both fresh tissues and cultured cells for expression of the PRL receptor messenger ribonucleic acid using the techniques of reverse-transcriptase polymerase chain reaction and Southern blotting. 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 amplified from both fresh and cultured tissues and con-firmed by Southern blotting and sequencing. Conclusions: PRL appears to be an autocrine or paracrine growth factor for both leiomyoma and myometrial cells. However, there are some differences between tissues in their sensitivity to this growth factor.