IJCS | Volume 32, Nº2, May/June 2019

244 Figure 4 - Maximum vascular relaxation induced by grape juice samples in aortas of rats pre-contracted with phenylephrine. The bars represent the maximal relaxation percentage (Emax) with or without treatment with L-NAME (100 μM, 30 min). * Significant difference (p < 0.05) vs. Control (with no L-NAME). Maximal relaxation (%) Control + L-NAME Britto Junior et al. Antioxidant and vasodilatory action of grape juices Int J Cardiovasc Sci. 2019;32(3)238-246 Original Article one of the main tools to determine antioxidant activity. In fact, good electron-donating agents (antioxidants) can reversibly oxidize at lower peak potentials (Epa < 0.5 mV, pH = 7). Following this idea, the concept of electrochemical index (EI) was previously proposed to qualify compounds with antioxidant capacity. 15 The evaluation of antioxidant activity using spectrophotometric and electrochemical methods shows that the analyses conducted with the classical methods (DPPH, ABTS and FC) agree with the electrochemical index, which allows the comparison of the antioxidant activity measured by electroanalytical methods. The small differences presented in the analyses are due to the color of the analyte, which generates interference in the spectrophotometric tests. In these analyses, the RJ sample also presented the best antioxidant activity, while the SP sample was the worst of them. The decreasing order of antioxidant activity obtained by EI calculations was: RJ ≥ GO ≥ RS (1) ≥ PR ≥ RS (2) > SP. Differential pulse voltammetry (Figure 2B) of the best (RJ) and worst (SP) sample had two anode peaks, one with Epa approximately at 0.1V and the other at 0.6V. Therefore, it can be stated that the electroactive species found in the juice are oxidizing at a low potential and this behavior is observed in samples that are rich in antioxidants. 16 Resveratrol, a phenolic compound that is very present in the grapes, oxidizes at a potential close to 0.6V; this finding justifies the presence of the second peak (2 a ) presented in the voltammogram. 17 Several studies report that the ingestion foods rich in polyphenols (mainly vegetables, fruits, wines and teas) are associated with a protective effect on the cardiovascular system in humans and animals. 18 In most published studies, red wine was highlighted as a functional food that is used to test the benefits of intake of antioxidants. Its effects include vascular dilatation in laboratory animals or patients with or without hypertension. 19,20 However, not only red wines can induce protection against cardiovascular risk factors. Many researchers have shown that the consumption of other beverages such as grape juice and teas can bring important benefits, often comparable to those of wine. 5,21 Our results showed that the different juice samples produced different cardiovascular results, having different levels of efficacy in the induction of vascular relaxation. The RJ sample was the one that presented the best result, being the only one that induced vascular relaxation at a similar level to the red wine tested. This result may be associated with a greater quantity of phenolic compounds, whose vasodilatory and cardioprotective action has been well documented. 22-24 Multiple mechanisms contribute to the beneficial action of polyphenol-rich beverages on the cardiovascular system, including direct effects on smooth muscle or