Infusion Of L-arginine Research Articles

Effects of long‐term intravenous and intragastric l‐arginine intervention on jejunal motility and visceral nitric oxide production in the hyperdynamic compensated endotoxaemic pig

Alterations in L-arginine availability and nitric oxide (NO) synthesis in the intestinal muscularis may contribute to disturbed small intestinal motility that is observed during endotoxaemia. The aim of this study was to evaluate the effect of L-arginine infusion on visceral NO production and jejunal motility in hyperdynamic compensated endotoxaemic pigs. Fasted and saline-resuscitated pigs were intravenously infused for 24 h with endotoxin (lipopolysaccharide, 50 ng kg(-1) min(-1)) or saline (n = 6). Endotoxaemic pigs received either intravenous L-arginine (n = 6, 5.3 micromol kg(-1) min(-1)) or L-alanine (isocaloric, n = 6). After 24 h, intravenous L-arginine or L-alanine infusion was continued intragastrically for 32-h in an enteral meal. During (0-24 h) and 1 day postendotoxaemia (48-56 h), jejunal motility was recorded by manometry and analysed for migrating motor complex (MMC) characteristics. Visceral NO production was measured at 24 and 48 h by 15N2-arginine-to-15N-citrulline conversion. Visceral NO production was increased during endotoxaemia and was higher in L-arginine than in L-alanine-treated pigs. One day postendotoxaemia, visceral NO synthesis was still increased in L-arginine but not in L-alanine-treated animals. Endotoxaemia shortened the MMC cycle duration and accelerated the MMC propagation velocity. Both were restored by L-arginine. Similar motility disturbances were observed one day postendotoxaemia and were also compensated by L-arginine infusion.

L-Arginine uptake affects nitric oxide production and blood flow in the renal medulla.

Experiments were performed to determine whether L-arginine transport regulates nitric oxide (NO) production and hemodynamics in the renal medulla. The effects of renal medullary interstitial infusion of cationic amino acids, which compete with L-arginine for cellular uptake, on NO levels and blood flow in the medulla were examined in anesthetized rats. NO concentration in the renal inner medulla, measured with a microdialysis-oxyhemoglobin trapping technique, was significantly decreased by 26-44% and renal medullary blood flow, measured by laser Doppler flowmetry, was significantly reduced by 20-24% during the acute renal medullary interstitial infusion of L-ornithine, L-lysine, and L-homoarginine (1 micromol.kg(-1).min(-1) each; n = 6-8/group). In contrast, intramedullary infusion of L-arginine increased NO concentration and medullary blood flow. Flow cytometry experiments with 4-amino-5-methylamino-2',7'-difluorescein diacetate, a fluorophore reactive to intracellular NO, demonstrated that L-ornithine, L-lysine, and L-homoarginine decreased NO by 54-57% of control, whereas L-arginine increased NO by 21% in freshly isolated inner medullary cells (1 mmol/l each, n > 1,000 cells/experiment). The mRNA for the cationic amino acid transporter-1 was predominantly expressed in the inner medulla, and cationic amino acid transporter-1 protein was localized by immunohistochemistry to the collecting ducts and vasa recta in the inner medulla. These results suggest that L-arginine transport by cationic amino acid transport mechanisms is important in the production of NO and maintenance of blood flow in the renal medulla.

L-arginine as a therapeutic tool in kidney disease

Infusion of L-arginine in experimental animals increases renal plasma flow (RPF) and glomerular filtration rate (GFR). It is likely that a component of these hemodynamic changes are mediated by nitric oxide (NO) as suggested by studies with specific antagonists of L-arginine metabolism. L-arginine administration ameliorates the infiltration of the renal parenchyma by macrophages in rats with obstructive nephropathy or rats with puromycin-induced nephrotic syndrome. L-arginine administration also blunts the increase in interstitial volume, collagen IV, and α-smooth muscle actin. Rats with a remnant kidney given 1% L-arginine in the drinking water had a greater GFR and RPF. L-arginine administration also decreased proteinuria. Diabetic rats given L-arginine had significantly lower excretion of protein and cyclic guanosine monophosphate than diabetic rats not receiving L-arginine. Despite persistent hyperglycemia, the administration of L-arginine prevented the development of hyperfiltration and ameliorated proteinuria in diabetic rats. In the setting of ischemic acute renal failure, the administration of L-arginine had a beneficial effect on GFR and RPF, decreased O 2 − production, diminished up-regulation of soluble guanylate cyclase, and prevented up-regulation of inducible NO synthase (iNOS). The pharmacokinetics of L-arginine indicate that side effects are rare and mostly mild and dose dependent.

KIDNEY GRAFT VASODILATORY RESERVE AND HIGH ENERGY PHOSPHATES METABOLISM (HEPS) IN TYPE 1 DIABETIC (T1DM)-UREMIC PATIENTS AFTER KIDNEY-ALONE (KA) OR KIDNEY-PANCREAS (KP) TRANSPLANTATION

P421 Aims: In T1DM patients with uremia which underwent kidney transplantation, both impaired glucose homeostasis and hypertension may significantly affect graft survival. Aim of our study was to assess whether vascular of metabolic markers or kidney disfunctions were detectable non-invasively in vivo in the transplanted patients depending on whether they received KA or KP transplantation. Methods: 20 KP and 15 KA patients matched for anthropometric features and plasma creatinine but with different HbA1c levels (6.4±0.7% and 8.6±0.6% in KP and KA respectively, P<0.05) underwent two procedures: 1) evaluation of renal blood flow with Magnetic Resonance Quantitative-flow (MR-Qflow) in the resting state and after i.v. L-arginine infusion to assess renal vasodilatory reserve 2) assessment of high energy phosphates (HEP) in the resting state using localized 31P-MR-Spectroscopy of the transplanted kidney. Both MR-Qflow and MRS protocols were performed using a 1.5T system (Gyroscan Intera; release 8; Philips). Results: Basal blood flow was similar in KP and KA and it increased significantly (+12.0±8.1%) after L-arginine administration in KP (p=0.02), but not in KA (-1.3±8.6%). At the same time a trend for a reduced inorganic phosphate (Pi)/βATP ratio was also evident in the KA (1.17±0.14) in comparison with KP (1.62±0.30). Conclusions: In summary, L-arginine-dependent renal vasodilatory response was demonstrated in KP patients using MR-Qflow technique and it resulted to be blunted in KA patients. Altered HEPs metabolism in the transplanted organ was also evident in KA in comparison with KP patients using 31P-MRS. In conclusion, correction of diabetes in KP along with that of uremia was shown to be associated with better vascular and metabolic features of the transplanted kidney than in KA; both MR-Qflow and MRS techniques may be useful tools to reveal early alterations of renal function in the transplanted organs.

Effects of acute L-arginine infusion on non-stress test in hypertensive pregnant women

Objective: The present report evaluates the effect of acute L-arginine administration on fetal heart variables by a computerized non-stress test (NST) analysis.Methods: Fifteen pregnant women at 30–34 weeks of gestational age affected by mild to moderate gestational hypertension were enrolled in the study. The study was performed in the second and third days of hospitalization. Each woman received both active (Arg) or placebo treatment (Placebo), in a double-blind, randomized, cross-over design. Women received saline infusion for 40 min, then they were infused with either placebo (saline infusion prepared by Damor Pharmaceutics and labeled as Arg-B) or Arg (L-Arg 20 g/500 ml labeled as Arg-A).Results: Multiple analysis of variance (MANOVA) indicated that both placebo and Arg infusion were unable to affect cardiac variables and fetal movements. As far as maternal blood pressure changes were concerned, MANOVA indicated that active treatment showed an acute hypotensive effect on both systolic (F = 8.98, p < 0.001) and diastolic values (F = 15.78, p > 0.001). Conversely, placebo infusion does not seems to have induced any change. Considering each time of infusion we observed that Arg treatment was able to lower systolic and diastolic blood pressure after the 40 min of infusion, with this effect persisting for 20 min.Conclusions: These data indicate that the acute, intravenous administration of high-dose L-arginine does not induce significant changes in fetal heart rate (FHR), whereas it lowers maternal blood pressure. Such conclusions are reinforced by the observation that saline administration in the same pregnant women was neutral for both FHR and maternal blood pressure values. According to previous studies, it seems conceivable that maternal L-arginine treatment enters the fetal circulation by crossing the placenta. The lack of changes in FHR, however, suggests that no significant hemodynamic changes were induced by the treatment. Contrary to what happens in the mother, this may possibly be due to a low, if any, conversion of L-arginine to nitric oxide in the fetus.

L-arginine supplementation does not inhibit neointimal formation after coronary stenting in human beings: an intravascular ultrasound study

Background In-stent restenosis results from neointimal tissue proliferation. L-arginine supplementation improves endothelial function and reduces neointimal formation after arterial injury in animals. The aim of the study was to assess the influence of L-arginine administration on neointimal proliferation after coronary stenting in human beings. Methods We performed a prospective, randomized, double-blinded, placebo-controlled study in 60 men without diabetes. L-arginine/placebo was administered intravenously 12 hours before percutaneous coronary intervention (200 mg/kg for 240 minutes), during the procedure (200 mg/kg for 240 minutes), and intracoronarily immediately before stent implantation (500 mg for 10 minutes), and it was followed by oral treatment for next 2 weeks (6.0 g/d). By quantitative coronary angiography, late lumen loss, and intravascular ultrasound, neointimal volume and percent neointimal volume were calculated after 7 months of follow-up to assess neointimal formation. Results There were no differences in baseline clinical or angiographic characteristics between the two groups. Intravenous infusion of L-arginine increased plasma L-arginine concentrations 6-fold compared with placebo (661 ± 264 vs 107 ± 71 mmol/L, P < .001). During the 2-week period of oral treatment with L-arginine there was a sustained, significant increase of plasma L-arginine level (150 ± 50 vs 100 ± 17, P < .001, 135 ± 42 vs 89 ± 27, P < .001, respectively, on days 7 and 14 in the L-arginine group vs placebo). However, at 7-month follow-up, there was no difference in neointimal formation measured both by quantitative coronary angiography and intravascular ultrasound between the study groups. Conclusions Chronic systemic L-arginine administration has no effect on neointimal formation after coronary stenting in human beings.

Asymmetrical dimethylarginine: the Uber marker?

The traditional risk factors of hypercholesterolemia, hypertension, diabetes mellitus, and tobacco exposure identify a subset of patients at greater cardiovascular risk. A variety of clinical phenotypes, biochemical markers, and genetic polymorphisms have been proposed to explain the variance in risk not explained by the traditional factors. Notably, all of the traditional risk factors, as well as the great majority of new risk markers, are associated with endothelial vasodilator dysfunction. Because the end points (endothelial dysfunction leading to plaque formation, progression, and rupture) are the same, it follows that diverse risk factors ultimately share common pathways(s) of pathobiology. We and others have provided evidence for a ubiquitous mechanism of endothelial pathobiology shared by all risk factors and markers examined to date. This mechanism of endothelial derangement is mediated by an endogenous inhibitor of nitric oxide synthase (NOS), a molecule known as asymmetrical dimethylarginine (ADMA). Risk factors impair endothelial vasodilator function by causing the accumulation of ADMA. Furthermore, by blocking NO generation, ADMA initiates and promotes processes involved in atherogenesis, plaque progression. and plaque rupture. This review examines the burgeoning body of literature that supports ADMA as an “Uber marker,” a biochemical factor mediating the adverse vascular effects of many other risk factors and markers. Endothelial NOS converts the amino acid l-arginine into l-citrulline and NO. The importance of NO in vascular homeostasis has been discussed elsewhere.1 In addition to its vasodilator activity, NO inhibits key processes involved in vascular disease, including leukocyte adhesion, platelet aggregation, and vascular smooth muscle cell proliferation. In animal models, alterations in vascular NO synthesis profoundly influence the progression of atherosclerosis and restenosis.2–6 These experimental observations have gained greater significance with recent reports that impairment of the NOS pathway independently predicts cardiovascular events.7–11 Major causes of impairment of the NOS pathway are …

L-arginine-induced vasodilation of the renal vasculature is preserved in uremic type 1 diabetic patients after kidney and pancreas but not after kidney-alone transplantation.

In uremic type 1 diabetic patients, kidney and pancreas transplantation (KP) and kidney-alone transplantation (KD) provide full restoration of normal renal function; however, only KP, i.e., curing diabetes, is expected to prevent endothelial damages. Our aim was to study L-arginine-induced vasodilation of the renal vasculature in uremic type 1 diabetic patients after KP or KD using magnetic resonance (MR). MR quantitative flow measurements were performed in 15 KP patients (mean age 39.0 +/- 1.7 years, 10 men and 5 women), in 11 KD patients (mean age 47.3 +/- 1.9 years, 7 men and 4 women), and in 8 nondiabetic kidney transplant patients (mean age 44.0 +/- 4.8 years, 7 men and 1 woman), who were used as control subjects, to measure renal blood flow and velocity and renal vascular resistance before and immediately after infusion of L-arginine. Renal blood flow and velocity were not different at baseline in KP, KD, and control subjects. In contrast, during L-arginine administration renal blood flow increased significantly in KP subjects (basal 8.4 +/- 0.6 vs. post 9.6 +/- 0.8 ml/s, Delta 14.3 +/- 4.4%, P < 0.05) and in control subjects (basal 9.3 +/- 0.8 vs. post 9.1 +/- 0.8 ml/s, Delta 17.3 +/- 6.2%, P < 0.01), while it remained unchanged in KD subjects (basal 10.0 +/- 0.8 vs. post 11.6 +/- 0.9 ml/s, Delta -1.36 +/- 6.9%, NS). Parallel results have been achieved for renal blood velocity (KP subjects: 20.1 +/- 4.9%, P < 0.01; control subjects: 23.0 +/- 7.99%, P < 0.01; and KD subjects: -0.3 +/- 6.5%; NS). A reduction in renal vascular resistance in response to L-arginine was evident in KP and control subjects but not in KD patients. L-Arginine vasodilatory response was successfully assessed with MR quantitative flow measurements. KP patients and control subjects, but not those with KD, showed a preserved L-arginine-induced vasodilation of the renal vasculature.

Influence of l-arginine and vitamin C on the autonomic nervous system in chronic heart failure secondary to ischemic cardiomyopathy

In this study, we used spectral analysis to assess changes in respiratory recording variability during infusion of l-arginine and vitamin C, individually or together, in patients with chronic heart failure. We found that healthy subjects have a substantial ability to modulate sympathetic-mediated peripheral vascular resistance through endothelial synthesis of nitric oxide. Patients with chronic heart failure lose this ability.

Alterations of Renal Hemodynamics in Unilateral Ureteral Obstruction Mediated by Activation of Endothelin Receptor Subtypes

Unilateral ureteral obstruction (UUO) for 21 hours causes severe renal vasoconstriction. We examined the role of endothelin (ET)-A receptor in renal hemodynamic alterations induced by UUO. Hemodynamic and clearance experiments were performed in 3 groups of anesthetized dogs. In group 1, 6 sham operated dogs received intrarenal infusion of the specific ET-A receptor antagonist BQ-610 (Peninsula Laboratories, Inc., Belmont, California), followed by infusion of the nitric oxide synthase substrate L-arginine. In the 7 group 2 dogs release of 21-hour UUO was followed by intrarenal infusion of BQ-610 and L-arginine. In the 5 group 3 dogs release of 21-hour UUO was followed by L-arginine infusion. UUO caused marked decreases in renal blood flow (RBF) and glomerular filtration rate (GFR) in groups 2 and 3 compared with group 1. In group 1 BQ-610 and L-arginine infusion did not alter RBF or GFR. In contrast, BQ-610 infusion in group 2 after UUO release led to a significant increase in RBF and GFR as well as additional increases after L-arginine infusion. After UUO release in group 3 L-arginine infusion alone did not change RBF or GFR. After UUO release blockade of the ET-A receptor ameliorates renal vasoconstriction. The addition of L-arginine, which is a substrate for nitric oxide synthase, superimposed on ET-A receptor blockade confers a further decrease in renal vascular resistance, suggesting that the ET and L-arginine-nitric oxide systems are involved in renal hemodynamic alterations caused by UUO.

Effects of intravenous dobutamineon coronary vasomotion in humans

ObjectivesWe sought to investigate the vascular mechanisms of dobutamine-induced myocardial ischemia. BackgroundDobutamine stress is often used as a surrogate for exercise. The effects of dobutamine on the epicardial arteries are incompletely understood and possibly different from those of physical exercise. MethodsIntravenous (IV) dobutamine (40 μg/kg per min) was administered in 19 patients with normal, 23 patients with mildly atherosclerotic, and 12 patients with stenotic coronary arteries. In another two groups of patients with stenotic arteries, IV dobutamine was preceded by 1) an intracoronary (IC) bolus of the alpha-adrenergic blocker phentolamine (12 μg/kg, n = 12); and 2) an IC infusion of the nitric oxide substrate l-arginine (150 μmol/l per min for 20 min, n = 11). Intravenous saline instead of dobutamine was infused into eight patients with normal arteries. After dobutamine (or saline), an IC bolus of isosorbide dinitrate (ISDN, 0.2 mg) was given. Coronary vasomotion was evaluated by quantitative coronary angiography on angiograms obtained after each dose of dobutamine, saline, phentolamine, l-arginine, and ISDN. ResultsDobutamine increased the rate–pressure product and heart rate similarly in all patients except those who received saline. Dobutamine induced vasodilation in normal (change in luminal diameter [ΔLD] vs. baseline: 19 ± 2%) and in mildly atherosclerotic arteries (ΔLD: 8 ± 2%, p < 0.05 vs. normal). In stenotic arteries, dobutamine did not induce significant vasomotion (ΔLD: −3 ± 3%); the latter was improved by l-arginine (ΔLD: 10 ± 3%, p < 0.05 vs. stenotic arteries) and fully restored by phentolamine (ΔLD: 19 ± 3%, p < 0.05 vs. stenotic arteries). ConclusionsEndothelial dysfunction and enhanced alpha-adrenergic tone contribute to the loss of dobutamine-induced vasodilation in coronary atherosclerosis. In contrast to physical exercise, dobutamine does not induce “paradoxical vasoconstriction” of atherosclerotic coronary arteries.

A novel mechanism for pulmonary arterial hypertension?

The pathophysiology of primary pulmonary hypertension (PPH) involves alterations in vascular reactivity, vascular structure, and interactions of the vessel wall with circulating blood elements.1 An imbalance of vasodilator and vasoconstrictor influences is likely to be an early derangement. Progressive intimal and medial thickening, due to proliferation and migration of vascular smooth muscle cells and fibroblasts, reduces the cross-sectional area of the pulmonary microvasculature, causing fixed alterations in pulmonary resistance. Contributing to the progressive increase in pulmonary resistance is thrombosis of the small pulmonary vessels, which explains the benefit of anticoagulation in these patients. In advanced disease, “plexiform arteriopathy” of the small pulmonary vessels is observed. These lesions proliferate into the lumen, creating high-resistance, convoluted endoluminal channels. There is some controversy regarding the nature of the cells constituting these lesions, one group suggesting they are of endothelial origin, whereas more recent evidence indicates that they are myofibroblasts.2,3 See p 1493 The normal pulmonary endothelium maintains a low vascular resistance, suppresses vascular smooth muscle growth, inhibits platelet adherence and aggregation, and stems inflammation. In patients with PPH, the endothelium has lost these vasoprotective functions.1 The endothelium of the PPH patient is characterized by the increased elaboration of vasoconstrictors, mitogens, and prothrombotic and proinflammatory mediators (such as thromboxane, endothelin, plasminogen activator inhibitor, and 5-lipooxygenase). These endothelial alterations promote the pathophysiology of PPH. Furthermore, there is less influence of the countervailing factors prostacyclin and NO. Endothelium-derived NO plays a critical role in pulmonary …

Body sodium and volume homeostasis.

maintenance of a “milieu interieur,” which allows our cells to function away from the ancient sea, is one of the most important functions of the body. Maintenance of constant extracellular osmolarity and sodium concentration depends on a precise balance between intake and excretion of sodium and

L-Arginine-Induced Vasodilation of the Renal Vasculature Is Not Altered in Hypertensive Patients With Type 2 Diabetes

Diabetes, arterial hypertension, hypercholesterolemia, and aging are associated with endothelial dysfunction in various vasculatures. Endothelium-dependent vasodilation of the renal vasculature cannot be easily assessed, but infusion of L-arginine, the substrate of endothelial nitric oxide synthase, leads to an increase in renal plasma flow (RPF) in humans. We have examined the effect of L-arginine infusion on renal hemodynamics in hypertensive patients with type 2 diabetes. Twenty-three elderly patients with type 2 diabetes (age, 65 +/- 6 years; HbA(1c), 7.8 +/- 1.6%) with coexisting arterial hypertension (158 +/- 19/83 +/- 11 mmHg) and elevated cholesterol levels (total cholesterol, 215 +/- 33 mg/dl) were examined. These patients were compared with a young and healthy reference group (n = 20; age, 26 +/- 2 years). The effect of L-arginine infusion (100 mg/kg over 30 min) on RPF and glomerular filtration rate were measured using the constant input clearance technique with p-aminohippurate and inulin, respectively. L-arginine infusion similarly influenced renal hemodynamics in patients and reference subjects: RPF increased by 7 +/- 11 and 7 +/- 11% in diabetic and reference subjects, respectively (P = NS). Other parameters of renal hemodynamics such as glomerular filtration rate (5 +/- 5 vs. 4 +/- 4%) and filtration fraction (-1 +/- 8 vs. -1 +/- 9%) were not significantly different between diabetic and reference subjects, too. L-arginine-induced vasodilation of the renal vasculature is not different between a group of hypertensive diabetic patients and a young, healthy reference group. These data were obtained using low-dose L-arginine infusion.

Nitric oxide and prostacyclin play a role in the regulation of microvascular protein and hydraulic permeability in cat skeletal muscle.

To evaluate a possible role of nitric oxide (NO) and prostacyclin in the regulation of basal microvascular protein and hydraulic permeability. The study was performed on the autoperfused cat calf muscle. Changes in the osmotic reflection coefficient for albumin, calculated from the extended Starling equation, were used as a measure of altered protein permeability, whereas changes in capillary filtration coefficient (CFC) were used as a measure of altered hydraulic permeability. Inhibition of the endogenous NO production with L-nitro-arginine methyl ester given intra-arterially to the muscle decreased the reflection coefficient to 70% of the control (p < 0.05) and increased the CFC by 17% (p < 0.05). The addition of a simultaneous intra-arterial infusion of the NO precursor L-arginine restored both the reflection coefficient and the CFC back to control level. Blockade of the endogenous prostacyclin production with tranylcypromine given intra-arterially decreased the reflection coefficient to 72% of the control (p < 0.05) and increased the CFC by 24% (p < 0.05), and they were both restored to control levels by a simultaneous intravenous infusion of a nonvasodilating dose of prostacyclin (1.0 ng/kg per minute). The results support the view that endogenous NO and prostacyclin decrease both protein and hydraulic permeability. Assuming a dynamic endogenous release of these substances, they may act as bidirectional regulators of protein and hydraulic permeability.

Regulation of human cutaneous circulation evaluated by laser Doppler flowmetry, iontophoresis, and spectral analysis: importance of nitric oxide and prostaglandines

Nitric oxide (NO) and prostaglandines (PGs) are important in regulation of vascular tone and blood flow. Their contribution in human cutaneous circulation is still uncertain. We inhibited NO synthesis by infusing N G-monomethyl- l-arginine ( l-NMMA) in the brachial artery (16 μmol/min for 5 min) and reversed it by intraarterial infusion of l-arginine (40 μmol/min for 7.5 min). PG synthesis was inhibited by the cyclooxygenase inhibitor aspirin (600 mg over 5 min intravenously). Basal cutaneous perfusion and perfusion responses during iontophoresis with the endothelium-dependent vasodilator acetylcholine (ACh) and the endothelium-independent vasodilator sodium nitroprusside (SNP) were recorded by laser Doppler flowmetry (LDF). We performed wavelet transforms of the measured signals. Mean spectral amplitude within the frequency interval from 0.0095 to 1.6 Hz and mean and normalized amplitudes of five intervals around 1, 0.3, 0.1, 0.04, and 0.01 Hz were analysed. The oscillations with frequencies around 1, 0.3, 0.1, and 0.04 Hz are influenced by the heartbeat, the respiration, the intrinsic myogenic activity of vascular smooth muscle, and the neurogenic activity of the vessel wall, respectively. We have previously shown that the oscillation with a frequency around 0.01 Hz is modulated by the vascular endothelium. l-NMMA reduced mean value of the LDF signal by ≈20% ( P = 0.0067). This reduction was reversed by l-arginine. Mean value of the LDF signals during ACh and SNP iontophoresis did not change after infusion of l-NMMA. Aspirin did not affect mean value of the LDF signal or the LDF signal during ACh or SNP iontophoresis. Before interventions the only significant difference between the effects of ACh and SNP was observed in the frequency around 0.01 Hz, where ACh increased normalized amplitude to a greater extent than SNP. l-NMMA abolished this difference, whereas it reappeared after infusion of l-arginine ( P = 0.0084). Aspirin did not affect this difference ( P = 0.006). We conclude that basal cutaneous blood flow and the endothelial dependency of the oscillation around 0.01 Hz are partly mediated by NO, but not by endogenous PGs. Other aspects of human cutaneous circulation studied are not regulated by NO or PGs.

Evaluation of systemic blood NO dynamics by EPR spectroscopy: HbNO as an endogenous index of NO.

The measurement of hemoglobin-nitric oxide (NO) adduct (HbNO) in whole blood by the electron paramagnetic resonance (EPR) method seems relevant for the assessment of systemic NO levels. However, ceruloplasmin and unknown radical species overlap the same magnetic field as that of HbNO. To reveal the EPR spectrum of HbNO, we then introduced the EPR signal subtraction method, which is based on the computer-assisted subtraction of the digitized EPR spectrum of HbNO-depleted blood from that of sample blood using the software. Rats were treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; 120 mg. kg-1. day-1) for 1 wk to obtain HbNO-depleted blood. When this method was applied to the analysis of untreated fresh whole blood, the five-coordinate state of HbNO was observed. HbNO concentration in pentobarbital-anesthetized rats was augmented (change in [HbNO] = 1.6-5.5 microM) by infusion of L-arginine (0.2-0.6 g/kg) but not D-arginine. Using this method, we attempted to evaluate the effects of temocapril on HbNO dynamics in an L-NAME-induced rat endothelial dysfunction model. The oral administration of L-NAME for 2 wk induced a serious hypertension, and the HbNO concentration was reduced (change in [HbNO] = 5.7 microM). Coadministration of temocapril dose dependently improved both changes in blood pressure and the systemic HbNO concentration. In this study, we succeeded in measuring the blood HbNO level as an index of NO by the EPR HbNO signal subtraction method. We also demonstrated that temocapril improves abnormalities of NO dynamics in L-NAME-induced endothelial dysfunction rats using the EPR HbNO signal subtraction method.

Vitamin C, diclophenac, and l-arginine protect endothelium-dependent vasodilation against elevated circulating fatty acid levels in humans

An acute elevation of circulating non-esterified fatty acids (NEFAs) has previously been shown to impair endothelium-dependent vasodilation (EDV). In this study, we investigated if local administration of vitamin C ( n=8, 18 mg/min), l-arginine ( n=8, 12.5 mg/min), or the cyclooxygenase (COX) inhibitor diclophenac ( n=8, 0.5 mg/min) can counteract the endothelial dysfunction seen during infusion of Intralipid® plus heparin ( n=10). EDV and endothelium-independent vasodilation (EIDV) were studied in the forearm after local administration of methacholine chloride (Mch; 2 and 4 μg/min) and sodium nitroprusside (SNP; 5 and 10 μg/min). Forearm blood flow (FBF) was determined with venous occlusion plethysmography. Intralipid® and heparin increased circulating NEFA levels sevenfold and impaired EDV ( P<0.001 vs baseline). Concomitant administration of l-arginine or diclophenac abolished the NEFA-induced impairment in EDV. Concomitant vitamin C administration actually improved EDV ( P<0.05 vs baseline). NEFA elevation increased EIDV ( P<0.01), but this effect was not significant after l-arginine or diclophenac infusions. In conclusion, an acute elevation of circulating NEFAs led to impaired EDV. Administration of l-arginine, vitamin C or COX inhibition abolished this effect, suggesting that NEFAs might interact with endothelial vasodilatory function through multiple mechanisms.

Formation of Peroxynitrite following An Infusion of L-Arginine in Healthy Volunteers

Formation of Peroxynitrite following An Infusion of L-Arginine in Healthy Volunteers

Isotopic investigation of nitric oxide metabolism in disease.

Nitric oxide is an important mediator of both physiological and pathophysiological processes. Nitric oxide is produced during direct conversion of arginine to citrulline. Nitric oxide is rapidly metabolized, mainly to nitrite/nitrate, and finally excreted as urinary nitrate. For that reason, plasma and urinary nitrite/nitrate have been measured frequently as indicators of nitric oxide production, but it is becoming clear that these methods only give qualitative data. More recently, stable isotope methods have been introduced for quantitative measurement of nitric oxide production. This review aims at summarizing and evaluating these isotopic investigations of nitric oxide metabolism in disease. Different stable isotope methods are used to measure whole body nitric oxide production in vivo. These methods are all based on infusion of guanidino-labeled L-arginine and subsequent measurement of labeled products (e.g. nitrite/nitrate or citrulline). Nitric oxide synthesis in healthy individuals is found to be in the range of 0.2-1.0 micromol kg h, only 0.5-1% of arginine production. In diseased states, nitric oxide synthesis was found to be either decreased or increased. Increased nitric oxide synthesis was observed in gastroenteritis patients and in some animal models of sepsis. In patients with renal failure, however, both increased and decreased nitric oxide production have been reported. Nitric oxide production was not changed in familial hypercholesterolemia patients and after typhoid vaccination. Using stable isotopes to measure whole body nitric oxide production in vivo is the most accurate method to study quantitative changes in the nitric oxide production rate. This technique is easy to perform in both healthy and diseased individuals, requiring infusion of stable isotopes for only a few hours and blood sampling.