Effect of ovarian steroids and diethylstilbestrol on the contractile responses of the human myometrium and intramyometrial arteries.

Estriol, estradiol, progesterone and diethylstilbestrol in the concentration range of 0.2-40 microM inhibited the spontaneous contractions of the myometrium in a dose-dependent manner but the differences in IC50 values obtained with different hormones were not statistically significant. All these hormones caused a concentration-dependent inhibition of the K(+)-induced contraction. The IC50 values were lowest for diethylstilbestrol and highest for estriol. Vasopressin at concentrations of 1.5 x 10(-6) - 1.8 x 10(-3) U/ml stimulated myometrial contractions. These responses were also inhibited by ovarian steroids and diethylstilbestrol. The IC50 values for estriol and progesterone were significantly higher than for estradiol or diethylstilbestrol. The values for estriol and progesterone did not differ significantly. In the uterine arteries, which lacked spontaneous activity, ovarian steroids and diethylstilbestrol inhibited contractions induced by K+ depolarization. As with myometrium, the lowest effect was observed with estriol and the highest with diethylstilbestrol. A dose-dependent inhibition by all four hormones (0.2-40 microM) of vasopressin-induced contractile responses of the uterine arteries was observed. With the lowest concentration of progesterone, however, the arterial response to vasopressin was enhanced. The increases by progesterone (0.02 and 0.2 microM) of responses induced by vasopressin were statistically significant (P < 0.05). The present data strongly suggest that, in human myometrium and uterine arteries, ovarian steroids and diethylstilbestrol cause a more pronounced inhibition of receptor-mediated than of voltage-dependent Ca2+ channels. The increase by a very low (physiological) concentration of progesterone of vasopressin-induced responses in both myometrium and arteries may be of significance in the pathophysiology of dysmenorrhea.