Abstract

We report on the modulatory effects of chronic subcutaneous or oral estrogen and LY117018, a selective estrogen receptor modulator, on the release of nitric oxide in rings of rat aorta studied under isometric conditions. Dilator responses to acetylcholine (ACh; 10⁻⁸to 10⁻⁵ M) were obtained in phenylephrine (PE; 2 μM)-contracted aorta, and constrictor dose-response curves to PE (10⁻⁸ to 10⁻⁵ M) were generated before and after pretreatment with N^ω-nitro-l-arginine methyl ester (L-NAME; 200 μM), an inhibitor of nitric oxide synthase. Tissue segments were obtained from five groups of rats implanted with a subcutaneous pellet delivery system for 21 days: (1) male, (2) sham-operated placebo-treated female, (3) ovariectomized placebo-treated, (4) ovariectomized, 17β-estradiol treated (0.5 mg/pellet) and (5) ovariectomized, progesterone (15 mg/pellet) and 17β-estradiol (0.5 mg/pellet)-treated. Aortic rings from sham rats and ovariectomized rats receiving estrogen relaxed more to ACh (10⁻⁶ to 10⁻⁵ M) than did the rings from ovariectomized, progesterone plus estrogen-treated and male rats (P < .05). They were also characterized by a greater potentiation of the PE responses after L-NAME compared with male, progesterone plus estrogen-treated and ovariectomized rats (P < .05) and a similar sensitivity to PE. In addition, ACh-induced relaxation and L-NAME-induced potentiation of PE contractions in aortic rings from rats dosed orally with LY117018 were similar to responses of aortic rings from rats dosed orally with estrogen. These results demonstrate that chronically administered estrogen and LY117018 enhance the release of nitric oxide from endothelium in rat aortic rings.