Effect of in vivo estradiol administration to bilaterally ovariectomized rats on in vitro myometrial responsiveness to prostaglandin F2alpha 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 F2alpha. The first study investigated dose-dependent effects. Seven days after ovariectomy rats were given a single s.c. dose of corn oil (n = 4) or estradiol (5 microg, n = 5; 15 microg, n = 5; 50 microg, n = 4). A second identical injection of corn oil or estradiol was administered 24 h after the initial injection. Rats were killed 48 h after the first injection. A second study investigated time-dependent effects of estradiol treatment. A second group of ovariectomized rats received s.c. estradiol (50 microg) seven days after ovariectomy. These rats were killed either 12 h (n = 5) or 24 h (n = 4) after injection. Full-thickness cross-sections of uteri were suspended in vitro in the longitudinal direction in a superfusion system. Cumulative concentration-response curves were constructed to oxytocin and prostaglandin F2alpha. Both the duration and dose of estradiol treatment significantly (p < 0.05) attenuated baseline contractile activity, and the maximum myometrial response to oxytocin and prostaglandin F2alpha. Estradiol, in a dose-dependent manner, significantly reduced myometrial sensitivity (p < 0.05) for oxytocin and prostaglandin F2alpha.