Piceatannol 3'-O-glucoside, an active component of Rhubarb, activates endothelial nitric oxide ( NO ) synthase through inhibition of arginase activity with IC 50 s of 11.22 µM and 11.06 µM against arginase I and arginase II , respectively. In Vitro Piceatannol 3'-O-glucoside (Piceatannol-3'-O-β-D-glucopyranoside; PG) is a potent component of stilbenes, inhibits the activity of arginase I and II prepared from mouse liver and kidney lysates, respectively, in a dose-dependent manner. In human umbilical vein endothelial cells, incubation of Piceatannol 3'-O-glucoside markedly blocks arginase activity and increases nitrite and nitrate (NOx) production, as measured by Griess assay. In liver lysates, incubation of different concentrations of Piceatannol 3'-O-glucoside significantly decreases arginase I activity (75±5% at 1 µM, 72±7% at 3 µM, 62±1% at 10 µM) compared to untreated control (100±9%). In kidney lysates, the residual arginase activities after incubation of 1, 3 and 10 µM Piceatannol 3'-O-glucoside are 75±6, 74±5, and 53±8%, respectively. Arginase activity is measured in the presence of different concentration of Piceatannol 3'-O-glucoside (from 0 to 120 µM) using liver lysate and kidney lysate. The 50% inhibitory concentrations (IC 50 ) are 11.22 µM for the liver lysate and 11.06 µM for kidney lysate. The values are obtained using the software of Graphpad prizm 4.0. Piceatannol 3'-O-glucoside inhibits arginase activity and increases NO production in HUVECs. Piceatannol 3'-O-glucoside inhibits lipoxygenase activity upto 66% at the concentration of 100 µM and IC 50 value is 69 µM. MCE has not independently confirmed the accuracy of these methods. They are for reference only. In Vivo In order to ascertain whether Piceatannol 3'-O-glucoside (PG) ameliorates vascular function in wild-type (WT) and atherogenic model mice [apolipoprotein E- mice (ApoE -/- )] and to investigate the possible underlying mechanism. Preincubation of aortic vessels from WT mice fed a normal diet (ND) with Piceatannol 3'-O-glucoside attenuates vasoconstriction response to U46619 and phenylephrine (PE), while the vasorelaxant response to acetylcholine (Ach) is markedly enhanced in an endothelium-dependent manner. Piceatannol 3'-O-glucoside treatment attenuates the phenylephrine (PE)-dependent contractile response, and significantly improves the acetylcholine (Ach)-dependent vasorelaxation response in aortic rings from ApoE -/- mice fed a high-cholesterol diet (HCD). Piceatannol 3'-O-glucoside administration in the drinking water significantly reduces fatty streak formation in ApoE -/- mice fed an HCD. MCE has not independently confirmed the accuracy of these methods. They are for reference only. Animal administration Mice Twenty 10-week-old male wild-type (WT) (C57BL/6J) and ApoE -/- mice are studied. To determine the effect of Piceatannol 3'-O-glucoside on vascular reactivity, aortic rings isolated from 20 male C57BL/6J WT mice fed a normal diet (ND) and 20 male ApoE -/- mice fed an HCD are studied for 6 weeks. Aortic rings are incubated with or without Piceatannol 3'-O-glucoside (50 μM) for 18 h. For the pathological assay, Piceatannol 3'-O-glucoside is administered in the drinking water to ApoE -/- mice for 6 weeks when the mice are started on the HCD. Given that each mouse consumes ~10 mL water/day this represents a daily dose of ~500 μg/mouse/day of Piceatannol 3'-O-glucoside . aladdin has not independently confirmed the accuracy of these methods. They are for reference only. Form:Solid IC50& Target:NO synthase, IC50: 11.22 μM (Arginase I), 11.06 μM (Arginase II)