Effects of estradiol and interaction with progesterone or oxytocin on term human myometrial contractile activity

To investigate the effects of estradiol (E2) alone and in combination with progesterone or oxytocin on contractile activity of term human myometrium in vitro.

Myometrial specimens were obtained from 24 term pregnant women not in labor who underwent elective cesarean. Biopsies were kept in ice-cold and oxygenated Hepes buffer and buffer containing different hormonal solutions. The biopsies were dissected and mounted in tissue baths at 37 degrees C and isometric tension was recorded.

(1) Estradiol at 0.1 and 1 microgram/mL increased the contractile frequency (p < 0.01 for each), decreased the tonus (p < 0.05 and p < 0.01) and suppressed the activity area of contractions (p < 0.05 and p < 0.01) as compared to control. (2) No significant differences in frequency and activity area of contractions between strips superfused with E2 plus progesterone and progesterone alone were recorded. Myometrial tonus was decreased by 0.1 microgram/mL or 1 microgram/mL E2 plus progesterone as compared to progesterone alone (p < 0.05 and p < 0.01). (3) There were no significant differences in frequency between strips superfused with E2 plus oxytocin and oxytocin alone. Myometrial tonus was decreased by 0.1 microgram/mL or 1 micrograms/mL E2 plus oxytocin as compared with oxytocin alone (p < 0.05 and p < 0.01). Estradiol at 0.1 microgram/mL or 1 micrograms/mL plus oxytocin reduced the activity area of contractions compared to oxytocin (p < 0.05 and p < 0.01).

These data suggest that E2 had both stimulatory and inhibitory effects on term human myometrial contractility and that E2 altered the myometrial response to progesterone and oxytocin mainly by decreasing tonus.