UNEXPECTED STIMULATORY EFFECT OF PROGESTERONE ON HUMAN MYOMETRIAL CONTRACTILE ACTIVITY IN-VITRO

Objective: To investigate the effects of continuous exposure of proges terone on contractile activity of term human myometrium in vitro. Meth ods: Myometrial biopsy specimens were obtained from 14 term pregnant w omen undergoing elective cesarean. The specimens were immediately imme rsed in Hepes buffer and buff er containing 0.33, 4.1, and 70 mug/mL p rogesterone. Muscle biopsies were dissected along the bundles of smoot h muscle under stereomicroscope. These myometrial strips were mounted in tissue baths and superfused with Hepes buff er and buffer containin g different concentrations of progesterone. Results: The progesterone concentration of 0.33 mug/mL had no significant eff ect on myometrial contractile activity. The concentrations of 4.1 and 70 mug/mL increase d the frequency of contractions (P < .01 for each) and tonus (P < .01 for each), decreased the activity area of contractions (P < .01 for ea ch), and delayed the onset of contractions (P < .01 and P < .05, respe ctively). Conclusion: When the myometrium is not deprived of progester one, this hormone may have excitatory effects on the frequency of cont ractions and tonus of the lower uterine segment of term human myometri um.