n-3-Polyunsaturated fatty acids (PUFAs) protect against myocardial infarction, arteriosclerosis and high blood pressure by stimulating endothelial nitric oxide synthase (eNOS) to increase nitric oxide (NO) production. However, the mechanism remains to be elucidated. This study investigated the role of SIRT1 in the protective effects of docosahexaenoic acid (DHA) in vascular endothelial cells. Exposure of human umbilical vein endothelial cells (HUVECs) to 0.3-30 mu M DHA did not affect cell viability, and DHA treatment dose-dependently increased SIRT1 expression. The DHA-mediated increase in SIRT1 expression induced eNOS deacetylation, increasing endothelial NO. However, inhibition of SIRT1 inhibited DHA-mediated increases in NO production. This effect was mediated via deacetylation of lysines 496 and 506 in the eNOS calmodulin-binding domain. The effects of DHA were also demonstrated in rat aortic rings, in which DHA treatment increased SIRT1 expression and bioavailable NO. Our results demonstrate that SIRT1 plays an important role in DHA-mediated increases in bioavailable NO via decreased eNOS acetylation. (c) 2013 Elsevier Inc. All rights reserved.