Objective: Since zinc (Zn) and selenium (Se) are important components for cell protection against certain oxygen species it has been suggested that Zn and/or Se deficiency impairs the potent antioxidant defense capacity and may be involved in the initiation of endothelial dysfunction (1-5). However, there is a lack of functional studies to address this issue. The aim of this study was to determine if changes in dietary content of Zn and Se affect vascular responses in rat isolated carotid arteries. Methods: Fifteen male Sprague Dawley rats were fed with 3 types of custom made rat chow (Faculty of Agriculture University of Osijek, Croatia) from weaning for 10 weeks: a) high Zn(70.81mg/kg)-low Se(0.043mg/kg) group (N=5); b) high Se (0.363mg/kg)-low Zn(30.16mg/kg) group (N=5) and c) low Zn(28.56mg/kg)-low Se(0.03mg/kg) group (N=5). Prior to decapitation, rats were anesthetized with 75 mg/kg ketamine+2.5 mg/kg midazolam. Carotid arteries were isolated and their isometric tensions were measured by DMT multi-wire Myograph system. We tested dose responses to ACh (10-9-10-5 M) and response to reduced pO2 (in the bath bubbled with gas mixture containing N2 95%, CO2 5%) after precontraction with noradrenaline (NA) for 5 minutes, in the absence/presence of the NOS inhibitor L-NAME or COX-1,2 inhibitor indomethacin (INDO) in the tissue bath. Viability of rings at the end of the hypoxic relaxation protocol was tested with their ability to contract in bath solution bubbled with 95% O2-5% CO2 gas mixture. To compare differences between groups and treatments One-way ANOVA or t-test was used when appropriate. Statistical significance was set at P<0.05 (SigmaPlot v11.2). Results: ACh induced relaxation (AchIR) was significantly reduced in low Zn-low Se group and high Se-low Zn group compared to high Zn-low Se (P<0.001 for 10-7-10-4 M Ach concentration). L-NAME (P<0.001 for 10-7-10-4 M Ach concentration) and INDO (P<0.001 for 10-6-10-4 M Ach concentration) blocked AChIR in all three groups of rats. Hypoxia induced relaxation (HIR) was significant in all study groups. However, there was no difference in HIR among groups. L-NAME and INDO significantly blocked HIR in high Zn-low Se and high Se-low Zn groups. In low Zn-low Se group HIR was blocked only after INDO administration. Conclusions: These data suggest: 1) Zn and Se deficiency affected vascular response to ACh and reduced pO2 in rat isolated carotid arteries and 2) it seems that for ACh dependent relaxation Zn level is more important than Se level. Support: This study was supported by grants of Ministry of Science, Education and Sports, Croatia, #219-2160133-2034, #079-0790462-0450 and FP7-Marie Curie-SmART, Hungarian Natl. Sci. Res. Found (OTKA) K71591; T67984, MHT 2010/2011 SROP-4.2.1/b-10/2/KONV-2010-0012, SROP-4.2.2.A-11/1/KONV-2012-0024.