In Vitro: 3',4'-Dihydroxyflavonol (DiOHF) acutely preserves nitric oxide (NO) activity in the presence of elevated reactive oxygen species (ROS). DiOHF improves NO activity in diabetes by reducing Nox2-dependent superoxide production and preventing eNOS uncoupling to improve endothelial function. 3',4'-Dihydroxyflavonol reduces vascular contraction through Ca²⁺ desensitization in permeabilized third-order branches of rat mesenteric arteries.