Abstract 1304: Contribution of EETs to Flow-induced Dilation in Male ERβ-KO Mice
Flow/shear stress-induced dilation in isolated gracilis arterioles of male estrogen receptorα knockout (ERα-KO) and wild type (WT) mice were studied. Increases in perfusate flow from 0 to 10 μl/min elicited comparable increases in the diameter of arterioles from both WT and ERβ-KO mice. However, unlike in WT vessels in which NO and prostaglandins participate equally (~50% vs 50%) in the mediation of flow-induced dilation, in ERα-KO arterioles, L-NAME inhibited flow-induced dilation by ~18%, whereas indomethacin inhibited dilations by ~50%. The remaining portion of the dilation was eliminated by additional administration of PPOH or iberiotoxin (IBTX), inhibitors of cytochrome P450 (CYP)/epoxygenase and BKCa-channels, respectively. By using an EDHF bioassay and an electrophysiologic technique, we found that in the presence of 10 dyne/cm2 shear stress, the perfusate passing through donor vessels isolated from ERα-KO mice elicited smooth muscle hyperpolarization of endothelium-denuded detector vessels by -12.00 ± 2.2 mV, associated with an increase in diameter by 13.2 ± 1.4 μm. These responses were prevented by the presence of IBTX in detector vessels, or PPOH in donor vessels, indicating that epoxyeicosatrienoic acids (EETs), released into the perfusate from the endothelium of donor vessels stimulated by shear stress, are responsible for the hyperpolarization of smooth muscle of detector vessels via activation of BKCa channels. GC-MS analysis indicated a significant increase in the production of EETs in arterioles of ERα-KO compared to that of WT mice. Western blot analysis showed a significantly reduced expression of eNOS, and an enhanced expression (~40%) of aromatase, responsible for the conversion of testosterone to estrogen, in ERα-KO arterioles. Thus, in response to the reduced release of NO, EETs contribute to the mediation of flow-induced dilation in ERβ-KO arterioles, via an estrogen-dependent upregulation of CYP. This study reveals a specific pathway by which estrogen regulates arteriolar endothelial function via upregulating CYP activity to compensate for the impairment of NO synthesis in the male vasculature.