Arginina. Nessun effetto sulla produzione di NO/Vasodilatazione
No effect of short-term arginine supplementation on nitric oxide production, metabolism and performance in intermittent exercise in athletes.
Arginine supplementation has been shown to alleviate endothelial dysfunction and improve exercise performance through increasing nitric oxide production in patients with cardiopulmonary diseases. In addition, arginine supplementation could decrease accumulations of lactate and ammonia, metabolites involved in development of muscular fatigue. The aim of this study was to investigate the effect of short-term arginine supplementation on performance in intermittent anaerobic exercise and the underlying mechanism in well-trained male athletes. Ten elite male college judo athletes participated with a randomized crossover, placebo-controlled design. The subjects consumed 6 g/day arginine (ARG trial) or placebo (CON trial) for 3 days then performed an intermittent anaerobic exercise test on a cycle ergometer. Blood samples were collected before supplementation, before and during exercise and 0, 3, 6, 10, 30 and 60 min after exercise. ARG trial had significantly higher arginine concentrations than CON trial at the same time point before, during and after exercise. In both trials, nitrate and nitrite concentration was significantly higher during and 6 min after exercise comparing to the basal concentration. The increase in nitrate and nitrite concentration during exercise in both trials was parallel to the increase in plasma citrulline concentrations. There was no significant difference between the 2 trials in plasma nitrate and nitrite, lactate and ammonia concentrations and peak and average power in the exercise. The results of this study suggested that short-term arginine supplementation had no effect on nitric oxide production, lactate and ammonia metabolism and performance in intermittent anaerobic exercise in well-trained male athletes
Effects of dietary L-arginine intake on cardiorespiratory and metabolic adaptation in athletes.
To assess the effect of diet enrichment with L-arginine or supplementation at high doses on physiological adaptation during exercise, 9 athletes followed 3 different diets, each over 3 consecutive days, with a wash-out period of 4 d between training sessions: control diet (CD), 5.5 +/- 0.3 g/d of L-arginine; Diet 1 (rich in L-arginine food), 9.0 +/- 1.1 g/d of L-arginine; and Diet 2 (the same as CD but including an oral supplement of 15 g/d), 20.5 +/- 0.3 g/d of L-arginine. Plasma nitrate levels of each participant were determined on the day after each treatment. Participants performed a submaximal treadmill test (initial speed 10-11 km/hr, work increments 1 km/hr every 4 min until 85-90% VO2max, and passive recovery periods of 2 min). Oxygen uptake and heart rate were monitored throughout the test. Blood lactate concentration ([La-]b) was determined at the end of each stage. Repeated-measures ANOVA and paired Student’s t tests were used to compare the various physiological parameters between diets. The level of significance was set at p < .05. [La-]b showed a significant effect at the 5-min time point between CD and Diet 2 (CD 3.0 +/- 0.5 mM, Diet 2 2.5 +/- 0.5 mM, p = .03), but this tendency was not found at higher exercise intensities. No significant differences were observed in any of the cardiorespiratory or plasma nitrate levels. In conclusion, dietary L-arginine intake on the days preceding the test does not improve physiological parameters during exercise.
Acute supplementation with the nitric oxide precursor L-arginine does not improve cardiovascular performance in patients with hypercholesterolemia.
Endothelial dysfunction based on lack of nitric oxide (NO) may contribute to several settings of cardiovascular disorder. Chronic oral supplementation with the NO precursor L-arginine counteracts the development of aortic atherosclerosis in cholesterol-fed rabbits, and i.v. infusion of L-arginine may acutely improve endothelium-dependent coronary epicardial vasodilation in patients with hypercholesterolemia (HC). To clarify whether excess NO precursor may also improve general cardiovascular performance in HC, we measured working capacity indices of myocardial ischemia, and basal and post-occlusive forearm and skin blood flow in nine patients with elevated plasma cholesterol (9.1 +/- 0.2 mumol/l) following random double-blinded administration of L-arginine (16 g i.v.) or placebo. Infusion of L-arginine raised the plasma concentration of this amino acid from 85 +/- 12 to 2460 +/- 230 mumol/l but did not change the plasma level of the major NO metabolite nitrate. Maximal working capacity, indices of myocardial ischemia, and basal and post-occlusive blood flow in the skin or forearm did not differ between the treatments. The lack of positive effect of L-arginine compared to placebo indicates that excess NO precursor did not improve microvascular endothelial function in the patients, or alternatively, that the indices measured in the present study were not dependent on endothelial microvessel function. Thus, in patients with HC, deficiency of precursor for NO formation does not seem to impair either maximal exercise capacity myocardial perfusion during maximal exercise, or maximal vasodilator capacity in skeletal muscle or skin.
L-arginine supplementation in peripheral arterial disease: no benefit and possible harm.
BACKGROUND: L-arginine is the precursor of endothelium-derived nitric oxide, an endogenous vasodilator. L-arginine supplementation improves vascular reactivity and functional capacity in peripheral arterial disease (PAD) in small, short-term studies. We aimed to determine the effects of long-term administration of L-arginine on vascular reactivity and functional capacity in patients with PAD. METHODS AND RESULTS: The Nitric Oxide in Peripheral Arterial Insufficiency (NO-PAIN) study was a randomized clinical trial of oral L-arginine (3 g/d) versus placebo for 6 months in 133 subjects with intermittent claudication due to PAD in a single-center setting. The primary end point was the change at 6 months in the absolute claudication distance as assessed by the Skinner-Gardner treadmill protocol. L-arginine supplementation significantly increased plasma L-arginine levels. However, measures of nitric oxide availability (including flow-mediated vasodilation, vascular compliance, plasma and urinary nitrogen oxides, and plasma citrulline formation) were reduced or not improved compared with placebo. Although absolute claudication distance improved in both L-arginine- and placebo-treated patients, the improvement in the L-arginine-treated group was significantly less than that in the placebo group (28.3% versus 11.5%; P=0.024). CONCLUSIONS: In patients with PAD, long-term administration of L-arginine does not increase nitric oxide synthesis or improve vascular reactivity. Furthermore, the expected placebo effect observed in studies of functional capacity was attenuated in the L-arginine-treated group. As opposed to its short-term administration, long-term administration of L-arginine is not useful in patients with intermittent claudication and PAD.
Dietary nitrate supplementation reduces the O2 cost of low-intensity exercise and enhances tolerance to high-intensity exercise in humans.
Pharmacological sodium nitrate supplementation has been reported to reduce the O2 cost of submaximal exercise in humans. In this study, we hypothesized that dietary supplementation with inorganic nitrate in the form of beetroot juice (BR) would reduce the O2 cost of submaximal exercise and enhance the tolerance to high-intensity exercise. In a double-blind, placebo (PL)-controlled, crossover study, eight men (aged 19-38 yr) consumed 500 ml/day of either BR (containing 11.2 +/- 0.6 mM of nitrate) or blackcurrant cordial (as a PL, with negligible nitrate content) for 6 consecutive days and completed a series of “step” moderate-intensity and severe-intensity exercise tests on the last 3 days. On days 4-6, plasma nitrite concentration was significantly greater following dietary nitrate supplementation compared with PL (BR: 273 +/- 44 vs. PL: 140 +/- 50 nM; P < 0.05), and systolic blood pressure was significantly reduced (BR: 124 +/- 2 vs. PL: 132 +/- 5 mmHg; P < 0.01). During moderate exercise, nitrate supplementation reduced muscle fractional O2 extraction (as estimated using near-infrared spectroscopy). The gain of the increase in pulmonary O2 uptake following the onset of moderate exercise was reduced by 19% in the BR condition (BR: 8.6 +/- 0.7 vs. PL: 10.8 +/- 1.6 ml.min(-1).W(-1); P < 0.05). During severe exercise, the O2 uptake slow component was reduced (BR: 0.57 +/- 0.20 vs. PL: 0.74 +/- 0.24 l/min; P < 0.05), and the time-to-exhaustion was extended (BR: 675 +/- 203 vs. PL: 583 +/- 145 s; P < 0.05). The reduced O2 cost of exercise following increased dietary nitrate intake has important implications for our understanding of the factors that regulate mitochondrial respiration and muscle contractile energetics in humans
Effects of dietary nitrate on oxygen cost during exercise.
AIM: Nitric oxide (NO), synthesized from l-arginine by NO synthases, plays a role in adaptation to physical exercise by modulating blood flow, muscular contraction and glucose uptake and in the control of cellular respiration. Recent studies show that NO can be formed in vivo also from the reduction of inorganic nitrate (NO(3) (-)) and nitrite (NO(2) (-)). The diet constitutes a major source of nitrate, and vegetables are particularly rich in this anion. The aim of this study was to investigate if dietary nitrate had any effect on metabolic and circulatory parameters during exercise. METHOD: In a randomized double-blind placebo-controlled crossover study, we tested the effect of dietary nitrate on physiological and metabolic parameters during exercise. Nine healthy young well-trained men performed submaximal and maximal work tests on a cycle ergometer after two separate 3-day periods of dietary supplementation with sodium nitrate (0.1 mmol kg(-1) day-1) or an equal amount of sodium chloride (placebo). RESULTS: The oxygen cost at submaximal exercise was reduced after nitrate supplementation compared with placebo. On an average Vo(2) decreased from 2.98 +/- 0.57 during CON to 2.82 +/- 0.58 L min(-1) during NIT (P < 0.02) over the four lowest submaximal work rates. Gross efficiency increased from 19.7 +/- 1.6 during CON to 21.1 +/- 1.3% during NIT (P < 0.01) over the four lowest work rates. There was no difference in heart rate, lactate [Hla], ventilation (VE), VE/Vo(2) or respiratory exchange ratio between nitrate and placebo during any of the submaximal work rates. CONCLUSION: We conclude that dietary nitrate supplementation, in an amount achievable through a diet rich in vegetables, results in a lower oxygen demand during submaximal work. This highly surprising effect occurred without an accompanying increase in lactate concentration, indicating that the energy production had become more efficient. The mechanism of action needs to be clarified but a likely first step is the in vivo reduction of dietary nitrate into bioactive nitrogen oxides including nitrite and NO.
Plasma arginine and citrulline kinetics in adults given adequate and arginine-free diets
The conversion of plasma citruiline to arginine approximated 5.5 ,umol*kg’l-hr-1 for the various groups and also was unaffected by arginine intake. Thus, endogenous arginine synthesis is not responsive to acute alterations in arginine intake in healthy adults. We propose that arginine homeostasis is achieved largely via modulating arginine intake and/or the net rate of arginine degradation.
Pharmacokinetics of intravenous and oral l-arginine in normal volunteers
Studies in humans have also demonstrated that total body arginine homeostasis is related to the rate of degradation by hepatic arginase . The activity of this enzyme is directly related to the concentration of arginine substrate
A single oral intake of arginine does not affect performance during repeated Wingate anaerobic test.
AIM: The ergogenic effect of arginine has been demonstrated in research focusing on its intake before exercise. However, in these studies, the effect of arginine in combination with other various metabolites were assessed. The aim of this study was to determine whether a single oral intake of arginine, without any other compounds, 60 minutes prior to exercise, modifies performance and exercise metabolism during a repeated Wingate anaerobic test. METHODS: Six healthy, active, but not highly trained volunteers participated in the study. Subjects performed three 30s all-out supramaximal Wingate Anaerobic Tests (WAnTs) with 4 minute-interval rest periods between WAnTs. RESULTS: Arginine ingestion before exercise did not influence physical performance. Triple WAnTs resulted in a marked increase in white blood cell (WBC) count, lactate and ammonia concentrations, however there were no differences between arginine and the placebo trials. CONCLUSION: Our data indicated that 2 g of arginine ingested in a single dose, neither induced nitrite/nitrate (NOx) concentrations changes, nor improved physical performance
Arginine does NOT increase NO during exercise
1: Med Sci Sports Exerc. 2009 Apr;41(4):773-9.Click here to read Links
Hemodynamic and vascular response to resistance exercise with L-arginine.
Fahs CA, Heffernan KS, Fernhall B.
Department of Kinesiology and Community Health, Exercise and Cardiovascular Research Laboratory, University of Illinois at Urbana-Champaign, Champaign, IL 61820, USA.
PURPOSE: L-arginine, the precursor to nitric oxide (NO), has been shown to improve endothelial function in patients with endothelial dysfunction. Resistance exercise has been shown to increase arterial stiffness acutely with no definitive cause. It is possible that a reduction in NO bioavailability is responsible for this. The purpose of this study was to examine the effect of acute L-arginine supplementation and resistance exercise on arterial function. METHODS: Eighteen (N = 18) young men (24.2 +/- 0.7 yr) volunteered for this study. In a crossover design, subjects underwent body composition testing, 1-repetition maximum testing for the bench press and the biceps curls and performed two acute bouts of resistance exercise in which they consumed either placebo or 7 g L-arginine before each resistance exercise bout. Anthropometric measures, augmentation index (AIx), arterial stiffness, and forearm blood flow (FBF) were assessed before and after each treatment condition. RESULTS: There were significant (P < 0.05) time effects after the resistance exercise; there was a reduction in brachial stiffness (P = 0.0001), an increase in central aortic stiffness (P = 0.004), an increase in AIx (P = 0.023), an increase in FBF (P = 0.000), and an increase in arm circumference (P = 0.0001) after exercise. CONCLUSIONS: The increase in central arterial stiffness and wave reflection was not attenuated by acute supplementation with L-arginine; furthermore, blood flow was not augmented with supplementation. On the basis of these data, l-arginine does not appear to change the hemodynamic and vascular responses to resistance exercise.