Docosahexaenoic acid (DHA) and eicosapentaenoic acids (EPA) are omega-3 fatty acids implicated in vasodilation of arteries (1). Vasodilation is mediated via numerous mechanisms including nitric oxide (NO), cyclooxygenase (COX) and the calcium activated potassium channels (KCa) such as large conductance KCa channels (BKCa). These channels have a major role in hyperpolarization and relaxation of vascular smooth muscle cells. Our preliminary studies in rat mesenteric artery indicated that inhibition of NO reduced EPA-induced vasodilation and inhibition of COX reduced DHA-induced vasodilation (2). Blockade of KCa channels also partially inhibited DHA-induced vasodilation (2). The aim of this study is to investigate if similar mechanisms are involved in fish oil-induced vasodilation of rat aorta. Wistar Kyoto rats were killed in accordance with the schedule one procedure of using an overdose of inhaled isoflurane. Arterial segments were mounted on a wire myograph (Danish myotechnology 400A) and the vasodilator effects of fish oils in rat aorta were investigated by cumulative concentration response curves pre-constricted with U46619 (10-500 nM). In some experiments L-NAME, a nitric oxide synthase (NOS) inhibitor (300 µM); paxilline, a BKCa blocker (1 µM) or high KCl Krebs, inhibitor of hyperpolarization mediated by potassium channels (30 mM), were administered prior to assessing relaxation. Vasodilation was expressed as mean % relaxation of U46619-induced constriction ± SEM of n animals. Data was analysed using one-way ANOVA with Bonferroni’s post-test. P-value of ≤ 0.05 was considered as being statistically significant. L-NAME caused partial blockade of DHA-induced vasodilation (3 µM DHA; 67.7±10.1% (Control) and 26.9±11.3% (L-NAME), P<0.05 n=5). Paxilline caused partial blockade of DHA-induced vasodilation (30 µM DHA; 86.9±2.3% (Control) and 58.7±7.6% (Paxilline), P<0.05 n=4). High KCl Krebs abolished DHA-induced vasodilation (30 µM DHA; 88±1.6% (Control) and 0.99±3% (High KCl Krebs), P<0.05 n=5). High KCl Krebs also inhibited EPA-induced vasodilation (30 µM DHA; 89.6±2.2% (Control) and 12.3±2.7% (High KCl Krebs), P<0.05 n=5). In rat aorta, inhibition of NOS and BKCa led to partial attenuation of DHA-mediated vasodilation. However, there was a major component of residual relaxation. We demonstrate that non-selective inhibition of hyperpolarization mediated by all potassium channels, almost completely inhibits both DHA and EPA-mediated vasodilation of rat aorta, indicating a critical role of potassium channels. Future studies will involve characterisation of these potassium channels in both rat aorta and mesenteric artery.