Efeitos agudos da ingestão do nitrato dietético nos parâmetros vasculares e de função endotelial de pacientes hipertensos tratados

Abstract

There is an attenuation of endothelium-derived relaxation factors such as nitric oxide (NO) in hypertension. Inorganic nitrate (NO3‾) from the diet may provide a physiological substrate for reducing nitrite (NO2‾) to NO. Studies suggest that inorganic NO3‾ has beneficial effects on cardiovascular health. The objective of this study was to evaluate the acute effects of dietary NO3‾ intake on the vascular function of hypertensive patients. A randomized, placebo-controlled, crossover study was performed in hypertensive patients of both sexes, aged between 40 and 70 years. The patients (n=37) included were submitted to clinical, nutritional and biochemical evaluation, blood pressure measurement, central hemodynamic parameters by aplanation tonometry (SphygmoCor) and oscillometry (Arteriograph), and microvascular reactivity by laser speckle contrast image (Pericam). After the tests, patients were submitted to the alternate single intake of beetroot juice (NO3‾) or mineral water (control), in the volume of 500ml. Tests of arterial stiffness and vascular function were performed after 150 minutes of intervention. The mean age was 59±7 years and 62% were women, with mean systolic and diastolic blood pressures of 142±10/83±9 mmHg. The NO3‾ (59.7±13.6 vs 169.4±76.9 µmol/L, p<0.001) and NO2‾ (0.099±0.014 vs 0.336±0.159 µmol/L, p<0,001) serum showed a significant increase after intervention with beetroot juice. In the control group, there were no significant differences in serum NO3‾ (56,4±26,5 vs 65,3±34,9 µmol/L, p=0,063) and NO2‾ (0,100±0,012 vs 0,095±0,018 µmol/L, p=0,162). There was a significant increase in augmented pressure (AP) (19±7 vs 21±9 mmHg, p=0,009) and aortic systolic blood pressure (aoSP) (137±15 vs 143±14 mmHg, p=0,003) in the control group, while there was attenuation of this increase in aortic AP (17±9 vs 19±8 mmHg, p=0.278) and aoSP (132±15 vs 136±16 mmHg, p=0.061) in the beetroot group. In the control group, there was no significant change in the subendocardial viability ratio (SEVR) (155±28 vs 160±28, p=0.080), although with a reduction in ejection duration (ED) (35±4 vs 34±4 ms, p=0.019) but there was a significant reduction in ED (37±4 vs 34±4 ms, p<0.001) and an increase in SEVR (149±25 vs 165±30, p<0.001) in the beetroot group. The % increase in perfusion (155 vs 159%, p=0.042) was significantly increased in the beetroot group, which was not observed after the control intervention (177 vs 148%, p=0.722). In the beetroot group, the change in SEVR showed a significant correlation with the change in area under the curve of post-occlusive reactive hyperemia (AUC-PORH) (r=0.45, p=0.012). The change in ED showed a significant correlation with the post-intervention perfusion peak (r= -0.37, p=0.031), peak cutaneous vascular conductance (CVC) after intervention (r= 0.37, p=0.031), and AUC-PORH post-intervention (r = -0.36, p=0.046). In conclusion, the ingestion of beetroot juice by hypertensive patients resulted in attenuation of central pressure and improvement of endothelial function, which was associated with greater subendocardial viability and higher performance in myocardial contraction.