PRODUCTION OF PROLACTIN BY SMOOTH-MUSCLE CELLS CULTURED FROM HUMAN UTERINE FIBROID TUMORS

Uterine leiomyomas, which are myometrial smooth muscle tumors, secrete PRL. We investigated the actions of several hormones known to stimula te PRL secretion by the pituitary gland or decidua on PRL secretion by leiomyoma-derived smooth muscle cells (SMC) in monolayer culture. Cul tures were verified to be SMC by immunostaining for smooth muscle alph a-actin and desmin. Hormone treatments were performed in serum-free me dium for 72 h. Medium was harvested every 24 h and assayed for PRL. 17 beta-Estradiol, progesterone, TRH, insulin-like growth factor-I, epide rmal growth factor, and the GnRH agonist leuprolide did not affect PRL secretion by these SMC. Insulin caused a significant suppression of P RL secretion by 72 h, and this was accompanied by a 64% increase in to tal cell protein per well, which represented an increase in cell numbe r. Cells were also plated at various densities to determine the effect s of cell number on PRL secretion. The amount of PRL secreted per 1000 cells decreased significantly as cell number per well increased. Nort hern blot analysis identified PRL mRNA in fresh leiomyoma tissue. PRL mRNA in three independent cultures of SMC was then detected by reverse transcription and the polymerase chain reaction. Hybridization occurr ed only with the expected band of approximately 423 basepairs in size. We conclude that leiomyomas express PRL mRNA in vivo and that leiomyo ma-derived SMC in culture continue to express the PRL mRNA and secrete PRL in the absence of ovarian steroids. PRL secretion by SMC in cultu re appears to be modulated primarily by changes in cell density.