EFFECT OF IN-VIVO ESTRADIOL ADMINISTRATION TO BILATERALLY OVARIECTOMIZED RATS ON IN-VITRO MYOMETRIAL RESPONSIVENESS TO PROSTAGLANDIN-F2-ALPHA AND OXYTOCIN

Bilaterally ovariectomized, nonpregnant female CD rats were studied to investigate the effect of estradiol treatment on in vitro myometrial responsiveness to oxytocin and prostaglandin F-2 alpha. The first stud y investigated dose-dependent effects. Seven days after ovariectomy ra ts were given a single s.c. dose of corn oil (n = 4) or estradiol (5 m u g, n = 5; 15 mu g, n = 5; 50 (mu g, n = 4). A second identical injec tion of corn oil or estradiol was administered 24 h after the initial injection. Rats were killed 48 h after the first injection. A second s tudy investigated time-dependent effects of estradiol treatment. A sec ond group of ovariectomized rats received s.c. estradiol (50 mu g) sev en days after ovariectomy. These rats were killed either 12 h (n = 5) or 24 h (n = 4) after injection. Full-thickness cross-sections of uter i were suspended in vitro in the longitudinal direction in a superfusi on system. Cumulative concentration-response curves were constructed t o oxytocin and prostaglandin F-2 alpha. Both the duration and dose of estradiol treatment significantly (p < 0.05) attenuated baseline contr actile activity, and the maximum myometrial response to oxytocin and p rostaglandin F-2 alpha. Estradiol, in a dose-dependent manner, signifi cantly reduced myometrial sensitivity (p < 0.05) for oxytocin and pros taglandin F-2 alpha.