Piceatannol (3, 3', 4, 5'-tetrahydroxy-trans-stilbene) is a naturally occurring phytochemical found in passion fruit (Passiflora edulis) seeds. Previously, we demonstrated that piceatannol has acute vasorelaxant effects in rat thoracic aorta. It was suggested that endothelial NO synthase (eNOS) might be involved in piceatannol-induced acute vasorelaxation. Here, we investigated the expression of eNOS in EA.hy926 human umbilical vein cells after long-term treatment with piceatannol, and compared this effect with that of resveratrol, an analog of piceatannol. Long-term treatment with piceatannol up-regulated eNOS mRNA expression and increased eNOS protein expression in a dose-dependent manner. Moreover, piceatannol increased the levels of phosphorylated eNOS. Treatment with resveratrol also increased eNOS expression, but to a lesser degree than piceatannol. These findings indicate that piceatannol may improve vascular function by up-regulating eNOS expression. (C) 2012 Elsevier Inc. All rights reserved.