Interaction of sex steroids and oxytocin on term human myometrial contractile activity in vitro.

Aug 1, 1994Obstetrics and gynecology

How sex hormones and oxytocin together affect contractions of human uterus muscle at term

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Abstract

Superfusion with progesterone plus oxytocin or estradiol reduced contraction activity in human myometrium.

Increased frequency of contractions was observed with progesterone plus oxytocin, progesterone plus estradiol, and their combination compared to buffer alone.
Decreased activity area and duration of contractions were noted with hormonal superfusion compared to buffer.
Higher concentrations of progesterone (5 micrograms/mL) plus oxytocin and progesterone plus estradiol elevated uterine tonus.
Lower concentrations of progesterone (0.5 microgram/mL) plus estradiol or their combination with oxytocin did not significantly affect tonus.
Progesterone and estradiol may directly influence uterine excitability and regulate the sensitivity to oxytocin.

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OBJECTIVE: To investigate the interactions of progesterone, estradiol (E2), and oxytocin in regulating the contractile activity of term human myometrium in vitro.

METHODS: Myometrial tissues from 12 term pregnant women were obtained from the lower uterine segment at elective cesarean and immediately immersed in Hepes buffer with and without progesterone and progesterone plus E2. Oxytocin was freshly dissolved in solutions when the superfusion was started. Muscle biopsies were dissected along the bundles of smooth muscle under a stereomicroscope, and the preparations were mounted in six tissue baths superfused with different hormonal solutions. The isometric tension was recorded during the experimental time.

RESULTS: During the 2-hour contraction period, increased frequency (P < .01 for each) and decreased activity area (P < .01 for each) and duration of contractions (P < .01 for each) resulted from superfusion of muscle strips with progesterone plus oxytocin, progesterone plus E2, and a combination of progesterone, E2, and oxytocin, compared to that found with buffer alone. The higher concentration of progesterone (5 micrograms/mL) plus oxytocin and progesterone plus E2 elevated the tonus (P < .05 and P < .01), whereas progesterone in combination with E2 and oxytocin decreased it (P < .05). The lower concentration of progesterone (0.5 microgram/mL) plus E2, or both in conjunction with oxytocin, had no significant effect on tonus as compared with buffer.

CONCLUSION: The results suggest that progesterone and E2 have a direct effect on uterine excitability and a regulating influence on the oxytocin sensitivity of term human myometrium.

Interaction of sex steroids and oxytocin on term human myometrial contractile activity in vitro.

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