engleski

Effects of dietary zinc and selenium on vascular responses to acetylcholine and reduced pO2 in aortic rings of male Sprague-Dawley rats

Objective: Increased oxidative stress is known to decrease the bioavailability of NO, affect cyclooxygenases (COX) activity and lead to impairment of vascular function (1, 2). Trace elements both zinc (Zn) and selenium (Se) are important components of antioxidative enzymes. Lack of Zn and Se in daily diet may be involved in the initiation of endothelial dysfunction (3-5). However, at the present there are no functional vascular studies to address this issue. The objective of this work was to determine if changes in dietary content of Zn and Se affect vascular responses in rat aortic rings. Materials and 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(70.81 mg/kg)-low Se(0.043 mg/kg) group (N=5) ; b) high Se (0.363 mg/kg)- low Zn(30.16 mg/kg) group (N=5) and c) low Zn(28.56 mg/kg)-low Se(0.030 mg/kg) group (N=5). Prior to decapitation, rats were anesthetized with 75 mg/kg ketamine+2.5 mg/kg midazolam. Thoracic aortic rings were used to test dose responses to Ach (10-9-10-5 M) and response to reduced pO2 (bath 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 95% O2-5% CO2 bath solution. To test differences among groups One- way ANOVA or t-test was used when appropriate. Statistical significance was set at P<0.05 (SigmaPlot v11.2, Systat Software, Chicago, USA). Results: ACh induced relaxation (AchIR) was significantly reduced in low Zn-low Se group compared to both high Zn-low Se and high Se-low Zn groups (P<0.001 for 10-7-10-4 M Ach concentration). L-NAME blocked AChIR in all three groups of rats (P<0.001 for 10- 7-10-4 M Ach concentration), while INDO significantly reduced AChIR only in high Se-low Zn group (P<0.01 for 10- 7-10-4 M Ach concentration). Hypoxia induced relaxation (HIR) was significant in all study groups. However, HIR was significantly reduced in high Se-low Zn group and low Zn-low Se group compared to high Zn-low Se group (P<0.01). L-NAME and INDO significantly blocked HIR in high Zn-low Se and low Zn-low Se groups and INDO reduced HIR more than L-NAME. In high Se-low Zn group HIR was blocked only after INDO administration. Conclusion: These data suggest: 1) Zn and Se deficiency affected vascular response to ACh and reduced pO2 in rat aortic rings ; 2) Zn deficiency may affect vascular NO system more than Se deficiency ; 3) adequate Se levels seem to have influence of the COX-dependant pathways ; and 4) it seems that for ACh dependent relaxation both microelements are equally important, while for HIR, adequate Zn level is more important.

zinc ; selenium ; vascular function ; aoric rings ; acetylcholine ; hypoxia

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