Improvement of Endothelial Dysfunction by Selective Estrogen Receptor-α Stimulation in Ovariectomized SHR

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Abstract
Both known estrogen receptors, ERα and ERβ, are expressed in blood vessels. To gain further insight into the role of ERα in a functional setting, we investigated the effect of the novel highly selective ERα agonist Cpd1471 on vascular reactivity in ovariectomized spontaneously hypertensive rats (SHR). After ovariectomy or sham operation, 12-week-old female SHR received either 17β-estradiol (E2, 2 μg/kg body wt per day), the selective ERα agonist Cpd1471 (30 μg/kg body wt per day), or placebo. Acetylcholine-induced endothelium-dependent vasorelaxation was significantly blunted in aortas from ovariectomized rats (R max , 53%±3% versus sham, 79%±2%; P max , 70%±2%; resp, 73%±2%). Endothelium-independent relaxation induced by sodium nitroprusside was not different among the four groups. The contractile response induced by the nitric oxide (NO) synthase inhibitor Nω-nitro- l -arginine, an index of basal NO formation, was significantly lower in ovariectomized rats compared with sham-operated animals (53±2% versus 77%±5%; P <0.01) and was normalized by both E2 (70%±2%) and Cpd1471 (70%±3%). Aortic endothelial NO synthase (eNOS) expression and phosphorylation of the vasodilator-stimulated phosphoprotein, an index of NO/cGMP-signaling, was reduced in ovariectomized SHR and normalized by E2 and Cpd1471. In SHR after ovariectomy, endothelium-dependent NO-mediated vasorelaxation and eNOS expression are attenuated. The novel selective ERα agonist Cpd1471 prevented these pathophysiological changes to a similar extent as E2. Thus, the pharmacological principle of selective ERα activation mediates positive vascular effects.