Potent inhibition by tamoxifen of spontaneous and agonist-induced contractions of the human myometrium and intramyometrial arteries

OBJECTIVE: Our purpose was to elucidate the mechanism of direct (nongenomic) action of antiestrogens on spontaneous and agonist-induced contractions of the human myometrium and uterine arteries. STUDY DESIGN: Myometrial strips and pieces of uterine arteries were obtained from nonpregnant premenopausal women undergoing hysterectomy. Spontaneous activity of myometrium and responses of myometrium and artery to K+-depolarization and vasopressin were recorded under isometric conditions. Quantification of the responses was done by planimetry. RESULTS: The 50% inhibitory concentration values for tamoxifen, clomiphene, and cycloferil in the case of myometrial spontaneous activity were 2.8, 43, and 331 nmol/L, respectively. Vasopressin-induced contractions in both the myometrium and arteries were potently inhibited by tamoxifen, and the 50% inhibitory concentration for the myometrium (1.4 nmol/L) was significantly lower (p < 0.05) than that for the arteries (11 nmol/L). Although tamoxifen caused no inhibition of responses induced by high potassium chloride (80 mmol/L), responses induced by low potassium chloride (20 mmol/L) were inhibited by 40% to 50% in both the myometrium and arteries. Glibenclamide reversed the inhibition by tamoxifen of spontaneous myometrial activity. CONCLUSIONS: Tamoxifen is a highly potent inhibitor of the contractile activity of the human nonpregnant myometrium and uterine arteries. It is suggested that tamoxifen could have strong potential in the treatment of dysmenorrhea.