Effects of nitrate supplementation in trained and untrained muscle are modest with initial high plasma nitrite levels.

Nitrate (NO3-) supplementation resulting in higher plasma nitrite (NO2-) is reported to lower resting mean arterial blood pressure (MAP) and oxygen uptake (VO2 ) during submaximal exercise in non-athletic populations, whereas effects in general are absent in endurance-trained individuals. To test whether physiologic effects of NO3- supplementation depend on local muscular training status or cardiovascular fitness, male endurance-trained cyclists (CYC, n=9, VO2 -max: 64±3 mL/min/kg; mean±SD) and recreational active subjects serving as a control group (CON, n=8, 46±3 mL/min/kg), acutely consumed nitrate-rich beetroot juice ([NO3-] ~9 mmol) (NIT) or placebo (PLA) with assessment of resting MAP and energy expenditure during moderate intensity (~50% VO2 -max) and incremental leg cycling (LEG-ex) and arm-cranking exercise (ARM-ex). NIT increased (P<.001) resting plasma NO3- by ~1200% relative to PLA. Plasma NO2- increased ~25% (P<.01) with a significant change only in CYC. LEG-ex VO2 (~2.60 L/min), ARM-ex VO2 (~1.14 L/min), and resting MAP (~87 mm Hg) remained unchanged for CYC, and similarly for CON, no changes were observed for LEG-ex VO2 (~2.03 L/min), ARM-ex VO2 (~1.06 L/min), or resting MAP (~85 mm Hg). VO2 -max was not affected by supplementation, but incremental test peak power was higher (P<.05) in LEG-ex for CYC in NIT relative to PLA (418±47 vs 407±46 W). In both CYC and CON, high initial baseline values and small increases in plasma NO2- after NIT may have lowered the effect of the intervention implying that muscular and cardiovascular training status is likely not the only factors that influence the physiologic effects of NO3- supplementation.

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.

In vitro evaluation of a new treatment for urinary tract infections caused by nitrate-reducing bacteria.

Dietary and endogenous nitrates are excreted in urine, and during infection with nitrate-reducing bacteria they are reduced to nitrite. At a low pH nitrite is converted to a variety of nitrogen oxides that are toxic to bacteria. We hypothesized that acidification of nitrite-rich infected urine would result in the killing of the nitrate-reducing bacteria. An Escherichia coli control strain and a mutant lacking nitrate reductase activity were preincubated in urine supplemented with sodium nitrate (0 to 10 mM) at pH 7.0. Then, the nitrite-containing bacterial culture was transferred (and diluted 1/10) to slightly acidic urine (pH 5 and 5.5) containing ascorbic acid (10 mM) and growth was monitored. The control strain produced nitrite in amounts related to the amount of nitrate added. This strain was killed when the culture was transferred to acidic urine. In contrast, the mutant that did not produce nitrite retained full viability. When control bacteria were grown in acidic urine with nitrate and ascorbic acid present from the start of the experiment, no inhibition of growth was noted. The MICs and minimal bactericidal concentrations of sodium nitrite-ascorbic acid in acidic urine were comparable to those of conventional antibiotics. Preincubation of nitrate-reducing E. coli in nitrate-rich urine leads to the accumulation of nitrite. Subsequent acidification of the urine results in generation of nitrogen oxides that are bactericidal. Killing, however, requires a sequential procedure in which the bacteria are first allowed to grow in a nitrate-rich neutral environment, later followed by acidification. We speculate that ingestion of nitrate followed some hours later by acidification of urine could be a new therapeutic strategy for the treatment of urinary tract infections.

Effect of combined nitric oxide inhalation and NG-nitro-L-arginine infusion in porcine endotoxin shock.

OBJECTIVE: To evaluate the possible effects of a combination of systemic nitric oxide synthesis inhibition (to increase mean arterial blood pressure) and nitric oxide inhalation (to decrease pulmonary vascular pressure) in porcine endotoxin shock. DESIGN: Prospective trial. SETTING: Laboratory at a large university medical center. SUBJECTS: Ten pathogen-free pigs weighing 19 to 25 kg. INTERVENTIONS: After surgical preparation, all pigs received a continuous infusion of Escherichia coli lipopolysaccharide endotoxin (15 micrograms/kg/hr) for 2 hrs. After 1 hr of endotoxemia, nitric oxide inhalation (50 parts per million) and NG-nitro-L-arginine infusion (50 mg/kg/hr) were initiated in six pigs. Four pigs served as controls and received only a lipopolysaccharide infusion. MEASUREMENTS AND MAIN RESULTS: NG-nitro-L-arginine infusion and nitric oxide inhalation prevented the further decrease in mean arterial blood pressure seen in the control pigs (p < .05), but did not restore mean arterial blood pressure back to basal values. Cardiac output decreased significantly compared with controls during NG-nitro-L-arginine infusion/nitric oxide inhalation (p < .01). Systemic vascular resistance, which was below basal values in the controls after 2 hrs of endotoxemia, was markedly increased by NG-nitro-L-arginine/nitric oxide, to higher values than those observed in the basal state (p < .01). In the control pigs, mean pulmonary arterial pressure and pulmonary vascular resistance showed a biphasic increase. In the NG-nitro-L-arginine/nitric oxide treated group, the second phase increase in mean pulmonary arterial pressure did not occur (p < .01). However, there was no difference in pulmonary vascular resistance between the groups. Renal vascular resistance was unchanged in controls, while NG-nitro-L-arginine/nitric oxide induced a four-fold increase in renal vascular resistance (p < .001). There was no statistical difference in urine production between the groups. PaO2 values were higher and PaCO2 tensions were lower in the treated pigs than in the controls. Arterial pH and base excess did not differ. Arterial plasma epinephrine, norepinephrine, and neuropeptide Y concentrations increased during the lipopolysaccharide infusion in both groups, with a tendency toward higher concentrations in the pigs receiving NG-nitro-L-arginine/nitric oxide. Arterial plasma endothelin-1-like immunoreactivity in these pigs was significantly higher at the end of the treatment than in the controls. CONCLUSIONS: In this model of porcine endotoxin shock, the combination of NG-nitro-L-arginine infusion and nitric oxide inhalation attenuated pulmonary hypertension and improved gas exchange; it also prevented development of further systemic hypotension, but impaired cardiac output and increased systemic and renal vascular resistances to supranormal levels. NG-nitro-L-arginine/nitric oxide did not reduce sympathetic nervous system activation or metabolic acidosis.

Inhibitory effects of diclofenac on the endotoxin shock response in relation to endothelin turnover in the pig.

During sepsis vasoactive arachidonic acid metabolites of the cyclo-oxygenase pathway and the endothelium-derived vasoconstrictor endothelin-1 (ET-1) are released. The effects of cyclo-oxygenase pathway inhibition by diclofenac on the endotoxin shock response and ET-1 turnover, were investigated in five groups of pigs. In the first group (n = 7; controls) endotoxin (15 micrograms.kg-1.h-1 i.v.) was infused for two hours. In a second endotoxin group (n = 7), the animals were pretreated with diclofenac (3 mg.kg-1 i.v.). In a third group (n = 7), high-dose ET-1 was infused (20 pmol.kg-1.min-1 i.v.) and in a fourth group (n = 7), the ET-1 infusion was preceded by diclofenac. In a fifth group (n = 4), a low and intermediate dose of ET-1 (0.2 and 4 pmol.kg-1.min-1) was infused. A significant increase in ET-1-like immunoreactivity (LI) plasma levels was observed in both endotoxin groups, but in the diclofenac group the increase was comparatively delayed. Furthermore, this group showed a more stable haemodynamic course and in the biphasic increase of pulmonary vascular resistance seen in endotoxin controls, the initial peak was abolished by diclofenac. Exogenous ET-1 infusion indicated that not only locally released but possibly also circulating ET-1 could be a mediator of vascular responses to endotoxin. Indications of release from the lungs were seen during endotoxin infusion. Diclofenac had no effect on basal ET-1-LI plasma levels or on the disappearance rate from plasma of ET-1-LI and the haemodynamic changes seen on ET-1 infusion. The inhibition of cyclo-oxygenase pathway by diclofenac resulted in prevention of the initial pulmonary hypertension and a delayed increase in plasma ET-1-LI levels in porcine endotoxin shock and this latter effect is not due to an increased rate of disappearance from plasma but rather to a decreased release of ET-1.