Induction of endometrial plasminogen activator-inhibitor 1: a possible mechanism contributing to the effect of intrauterine levonorgestrel in the treatment of menorrhagia.

ABSTRACT

OBJECTIVE: To elucidate molecular mechanisms accounting for excessive menstrual blood loss, and to present the therapeutic effect of an intrauterine levonorgestrel system (LNG-IUS) in menorrhagia. DESIGN: A multicenter study comparing hysterectomy with the LNG-IUS in treating menorrhagia. SETTING: A university hospital. PATIENT(S) Women with (n = 27) and without (n = 14) menorrhagia, and women with uterine fibroids but undetermined menstrual blood loss (n = 35). INTERVENTION(S) An LNG-IUS was inserted into the uterine cavity in 11 women with menorrhagia and six women experiencing normal menstrual blood loss. MAIN OUTCOME MEASURE(S) Expression of the messenger ribonucleic acid (mRNA) of tissue-type plasminogen activator (t-PA) and that of a specific PA inhibitor type 1 (PAI-1) in endometrial tissue samples, as evaluated with the use of Northern blot analysis. RESULT(S) t-PA mRNA was expressed in the endometrium throughout the menstrual cycle, with no statistically significant difference between a proliferative (n = 30) and a secretory endometrium (n = 40), or between women experiencing normal menstrual blood loss (n = 14) and those with menorrhagia (n = 27). The levels of t-PA mRNA in menstrual phase samples (n = 6) were significantly higher than those in proliferative or secretory endometrium. PAI-1 mRNA was detected in the endometrium during menstruation only. Both t-PA mRNA and PAI-1 mRNA were expressed in all endometrial samples (n = 17) obtained 6 months after an LNG-IUS was inserted, regardless of the menstrual cycle phase. The relative levels of both types of mRNA were significantly higher in LNG endometrium than in proliferative or secretory endometrium, but levels did not differ from those in menstrual-phase endometrium. CONCLUSION(S) The mean (+/-SD) levels of t-PA mRNA and PAI-1 mRNA in the endometrium of women with and without menorrhagia did not differ, suggesting that the PA system is not the major determinant of menstrual blood loss. However, continuous induction of PAI-1 may contribute to the therapeutic effect of LNG-IUS in treating menorrhagia.