Endothelin stimulation of rat uterine segment contractility is estrogen-dependent

To determine whether the effect of endothelin upon in vitro uterine contractility requires estrogen, immature female Long Evans rats were subcutaneously injected daily for 3 days with either estradiol benzoate or vehicle. The uterine contractile response to endothelin (5 or 100 nM) was measured. A response to endothelin in vehicle-treated animals exposed to physiologic (5.6 mM) or high (70.6 mM) potassium levels was also noted. Vehicle-treated uteri did not respond to endothelin; the contractions in estrogen-treated uteri increased by 288%. With high potassium, and without estrogen, no response to endothelin was seen. These data indicate that the contractile effect of endothelin on the uterus requires estrogen.