Paradoxical effect of L-arginine on nitric oxide (NO) synthesis and histopathological changes in 5/6 nephrectomized SD rats

Whether L-Arginine (L-ARG) ameliorates or aggravates renal function and histopathological changes in several models of renal disease remains controversial as L-ARG is the substrate for nitric oxide (NO) synthase as well as the precursor of proline and polyamines which cause renal fibrosis. These ambiguous results might be attributed to differences in the dose and period of L-ARG administration and the animal model used in each observation. Therefore, we tested the dose-dependent effect of L-ARG on mean blood pressure (MBP), 24-hour urinary excretion of protein (UP), NO metabolites (NO2(-) + NO3-) and cyclic GMP (cGMP), plasma asymmetrical dimethylarginine (ADMA), glomerular sclerosis index (SI) and % interstitial fibrosis area (%INT) in 5/6 nephrectomized SD rats. These 5/6 nephrectomized SD rats were divided into 4 groups: 1. L-ARG 0.2 g/kg/day (0.2 g ARG), 2. L-ARG 1 g/kg/day (1 g ARG), 3. L-ARG 2 g/kg/day (2 g ARG), 4. No administration of L-ARG(ARG(-)). Compared with ARG(-)MBP, UP and ADMA were significantly decreased and NO2(-) + NO3-, cGMP were significantly increased in the 0.2 g ARG. SI group and %INT were significantly increased in the 2 g ARG group and decreased in the 0.2 g ARG group. A small dose of L-ARG ameliorated glomerulosclerosis and interstitial fibrosis while a larger dose did not. SI, %INT and ADMA were inversely correlated with NO2(-) + NO3-. These data suggested that renal NO synthesis might attenuate glomerulosclerosis and interstitial fibrosis and the rise in ADMA and L-ARG might cause the decrease in NO.     

L-arginine supplementation in young renal allograft recipients with chronic transplant dysfunction.

AIMS: L-arginine (LA), the precursor of nitric oxide (NO), was suggested to be beneficial in many forms of renal disease: hypertension, ureteral obstructive nephropathy and cyclosporin A (CsA) nephrotoxicity. METHODS: Thus, we investigated the effects of LA supplementation on renal function, proteinuria and blood pressure (BP) in young renal allograft recipients with chronic renal transplant dysfunction treated with CsA. Eleven CsA-treated renal allograft recipients with chronic transplant dysfunction, aged 11-22 years, were randomly assigned to a 6-week treatment period with placebo (P), followed by 2 subsequent 6-week periods with LA supplementation (0.1 g/kg body weight/day) or a 6-week treatment period with LA, followed by 2 subsequent 6-week periods with P. At the end of each treatment period 24-hour BP recordings were made, and GFR (Inutest), RPF (PAH clearance) and the urinary excretion of protein, albumin, nitrate, cGMP and urea were evaluated. RESULTS: In comparison to placebo, LA treatment did not significantly change GFR, RPF, proteinuria and albuminuria, mean systolic or diastolic BP. The urinary excretion of urea and NO3 increased after LA supplementation (uUrea: LA 26.3 +/- 4.6 compared to P 23.5 +/- 4.7 g/day/1.73 m3, p < 0.05, uNO3: LA 514 +/- 152 compared to P 95 +/- 41 mM/day/1.73 m3, p < 0.05), whereas urinary excretion of cGMP remained unchanged. CONCLUSION: LA supplementation did not improve renal function and did not decrease proteinuria in CsA-treated renal allograft recipients with chronic transplant dysfunction possibly because of inhibition of NO-cGMP forming mechanism.     

Subpressor dose asymmetric dimethylarginine modulates renal function in humans through nitric oxide synthase inhibition

Increased blood concentrations of the endogenous nitric oxide (NO) synthase inhibitor asymmetric dimethylarginine (ADMA) have been linked to high blood pressure and to cardiovascular mortality. We evaluated the effects of a subpressor ADMA dose on NO production, renal hemodynamics, sodium handling and active renin and noradrenalin plasma concentrations in 12 healthy subjects (age 26 +/- 1 year) using a double-blind placebo-controlled study design. Infusion of ADMA caused a significant decrease in plasma cyclic guanosine monophosphate (cGMP) levels, i.e. the second messenger of NO (from 6.1 +/- 0.4 to 4.3 +/- 0.3 pmol/l; p < 0.05). In parallel, effective renal plasma flow (ERPF) decreased while renovascular resistance (RVR) increased significantly (ERPF from 667 +/- 9 to 603 +/- 10 ml/min/1.73 m2; RVR from 79 +/- 2 to 91 +/- 2 ml/min/mm Hg; both p < 0.05 vs. baseline). Infusion of placebo did not cause significant changes in plasma cGMP levels, ERPF and RVR (cGMP from 5.7 +/- 0.5 to 5.9 +/- 0.6 pmol/l; ERPF from 665 +/- 12 to 662 +/- 11 ml/min/1.73 m2; RVR from 79 +/- 2 to 78 +/- 2 ml/min/mm Hg; all non-significant). Moreover, urinary sodium excretion was significantly lower with infusion of ADMA as compared with placebo infusion (128 +/- 8 vs. 152 +/- 7 micromol/min; p < 0.05). In contrast, blood pressure, active renin and noradrenalin plasma concentrations did not change significantly with either infusion protocol. Acute infusion of a subpressor ADMA dose modulates several aspects of renal function in humans without affecting the activity of the renin-angiotensin and sympathetic system. Whether chronic (intrarenal) NO synthase inhibition in individuals with increased ADMA blood levels may cause persistent renal vasoconstriction and sodium retention must be evaluated.     

Total nitric oxide production is low in patients with chronic renal disease

BACKGROUND: A deficiency of the endogenous vasodilator nitric oxide (NO) has been implicated as a potential cause of hypertension in chronic renal disease (CRD) patients. This study was conducted to determine whether 24-hour NOX (NO2 and NO3) excretion (a qualitative index of total NO production) is reduced in patients with CRD. METHODS: Measurements were made in 13 CRD patients and 9 normotensive healthy controls after 48 hours on a controlled low-NOX diet. Urine was collected over the second 24-hour period for analysis of 24-hour NOX, and cGMP and blood drawn at the completion. Plasma levels of arginine (the substrate for endogenous renal NO synthesis), citrulline (substrate for renal arginine synthesis), and the endogenous NO synthesis inhibitor asymmetrical dimethylarginine (ADMA) and its inert isomer and symmetrical dimethylarginine (SDMA) were also determined. RESULTS: Systolic blood pressure was higher in CRD patients (12 of whom were already on antihypertensive therapy) than in controls (P < 0.05). Twenty-four-hour urinary NOX excretion was low in CRD patients compared with controls despite similar dietary NO intake, suggesting that net endogenous NO production is decreased in renal disease. In contrast, the 24-hour urinary cGMP did not correlate with UNOXV. Plasma citrulline was increased in CRD patients, possibly reflecting reduced conversion of citrulline to arginine. Plasma arginine was not different, and plasma ADMA levels were elevated in CRD versus controls, changes that would tend to lower NO synthase. CONCLUSION: These results suggest that NO production is low in CRD patients and may contribute to hypertension and disease progression in CRD.     

Oxalic Acid as a uremic toxin.

OBJECTIVE: Oxalic acid (OA) is thought to be a uremic toxin that participates in the pathogenesis of uremic syndrome. The objectives of this study were to: (1) evaluate the plasma levels of OA in patients with chronic renal disease with various levels of glomerular filtration rate and after renal transplantation; (2) investigate the salivary secretion of OA and ascorbic acid in healthy subjects and in patients with chronic renal failure (CRF); (3) examine the influence of water and sodium diuresis and furosemide administration on the urinary excretion of OA and ascorbic acid in healthy subjects and in CRF patients without dialysis treatment; and (4) evaluate the influence of renal replacement therapy (RRT) on secondary hyperoxalemia in hemodialysis patients. DESIGN AND SETTING: This study was conducted at the Nephrological Department of P.J. Safárik University. Sixty-one patients with chronic renal disease, 64 CRF patients, 32 continuous ambulatory peritoneal dialysis (CAPD) patients, 15 hemodialysis patients, 21 patients after renal transplantation, and 15 healthy subjects were examined. Maximal water diuresis, diets with low (2 g/day) and high (15 g/day) sodium intake, administration of intravenous furosemide (20 mg), and renal replacement therapy (CAPD, hemodialysis, hemofiltration, and postdilution hemodiafiltration) were utilized in the study. RESULTS: In patients with chronic renal disease and those after renal transplantation, direct relationships between plasma OA and serum creatinine were found (r = 0.904 and 0.9431, respectively, P < .01). Despite a high level of plasma OA in uremic patients (23.1 +/- 10 micromol/L), there was no significant difference in salivary OA between control subjects (128 +/- 19 micromol/L) and CRF patients (135 +/- 24 micromol/L). The urinary excretion of OA during maximal water diuresis (from 37.5 to 110.3 micromol/4 hours) and after intravenous furosemide (from 34.5 to 66.7 micromol/3 hours) increased significantly, but was not affected by high intake of NaCl. The most significant decrease of plasma OA was observed during postdilution hemodiafiltration (63.3%). CONCLUSION: Our study indicates that renal replacement therapy is not effective for a permanent reduction of elevated plasma levels of OA.     

Nitric oxide synthesis inhibition does not impair water immersion-induced renal vasodilation in humans

Nitric oxide (NO) is tonically released in the kidney to maintain renal perfusion and adequate sodium and water clearance. Little is known about the role of NO in the renal adaptation to an acute volume challenge. This is important for our understanding of pathophysiologic conditions associated with impaired NO activity. This study examined the effects of NO synthesis inhibition on neurohumoral, renal hemodynamic, and excretory responses to head-out immersion (HOI). Seven healthy men underwent four 7-h clearance studies. One study served as a time control study (placebo infusion), and in one study N(G)-monomethyl-L-arginine (L-NMMA; 3 mg/kg priming dose + 3 mg/kg per h) was infused during hours 2 to 5. In a third and fourth clearance study, HOI was applied from hours 3 to 5, during infusion of either placebo or L-NMMA. To assess the degree of NO synthesis inhibition, the effect of L-NMMA on [(15)N]-arginine-to-[(15)N]-citrulline conversion rate was studied in four others. HOI decreased mean arterial pressure (MAP) from 87 +/- 3 to 76 +/- 2 mmHg and renal vascular resistance (RVR) from 82 +/- 6 to 70 +/- 7 mmHg. min/L, and increased sodium excretion (UNaV) from 110 +/- 27 to 195 +/- 29 micromol/min and flow (UV) from 14.4 +/- 1.4 to 15.8 +/- 1.4 ml/min. L-NMMA caused profound and sustained increases in MAP and RVR and decreases in UNaV and UV. HOI superimposed on L-NMMA infusion decreased the elevated MAP from 93 +/- 4 to 83 +/- 2 mmHg and RVR from 111 +/- 9 to 95 +/- 7 mmHg. min/L, and increased UNaV from 41 +/- 8 to 95 +/- 15 micromol/min and UV from 10.0 +/- 1.1 to 12.7 +/- 1.4 ml/min. The relative changes were not significantly different from the effects of HOI without L-NMMA infusion. HOI decreased plasma renin activity and aldosterone and increased plasma atrial natriuretic peptide and urinary cGMP. L-NMMA decreased urinary cGMP, but did not affect the plasma hormones or the changes induced by HOI. L-NMMA decreased the [(15)N]-arginine-to-[(15)N]-citrulline conversion rate to one-third of baseline. The results indicate that in a state of NO deficiency in humans, the kidney can still respond to an acute volume challenge with vasorelaxation, diuresis, and natriuresis.     

Adrenomedullin and nitrite levels in children with minimal change nephrotic syndrome

Nitric oxide (NO) serves many functions within the kidney, and recent evidence suggests that NO contributes to glomerular injury. Adrenomedullin (AM) is a novel hypotensive peptide originally isolated from human pheochromocytoma. Recent studies showed that plasma AM concentrations correlated with the extent of proteinuria. We have examined the possible role of these two agents by studying plasma and urinary total nitrite (NO⁻ ₂ + NO⁻ ₃) and AM levels in children with minimal change nephrotic syndrome (MCNS). In comparison with healthy controls, children with MCNS had increased urinary nitrite excretion (μmol/mg urinary creatinine), irrespective of whether the disease was in relapse or remission (3.2±0.2 in relapse, n=13; 1.9±0.3 in remission, n=12; 1.0±0.2 in controls, n=10, P<0.05). Plasma nitrite levels (μmol/l) were high in relapse compared with controls (53.2±8.7 vs. 32±4.0, P<0.05). Plasma AM levels (pmol/ml) were decreased in relapse (27.6±1.4 in relapse, 43.3±1.2 in remission, 41.5±1.6 in controls, P<0.05). Urinary AM levels (pmol/mg urinary creatinine) were significantly higher in relapse than in remission and in controls (156±43 in relapse, 56±18 in remission, 36±16 in controls, P<0.05). Our data indicate that NO may play a role in mediating the clinical manifestations of MCNS in children. However, changes in AM levels may be the result of heavy proteinuria. Received: 20 December 1999 / Revised: 12 June 2000 / Accepted: 15 June 2000     

Assay of GBM antigen in urine and serum with an anti-human renal monoclonal antibody

Using a monoclonal antibody (Mab-G3) recognizing glomerular basement membrane (GBM), we assayed GBM antigen (G3-Ag) in the urine and serum of renal disease patients by sandwich ELISA. The subjects included normal control (NOR), minimal change nephrotic syndrome (MCNS), IgA nephropathy (IgA), membranous nephropathy (MN), membranoproliferative glomerulonephritis (MPGN) and chronic renal failure (CRF). The urine and serum was used as the material. With urinary G3-Ag, there were no statistically significant differences among the NOR, MCNS, IgA, MN, MPGN and CRF groups. Although no correlation was observed with proteinuria, hematuria, serum creatinine, serum beta 2 microglobulin and urinary NAG, urinary G3-Ag showed a significant (p less than 0.05) increase in excretion in the group of progressive CRF patients with s-Cr more than 1.0 mg/dl/month as compared to the stationary CRF group with s-Cr less than 1.0 mg/dl/month. Serum G3-Ag showed lower values in almost all cases, and there were no significant differences among the renal disease groups. The above findings led us to believe that the assay of urinary G3-Ag was useful in determining the degree of GBM disorder. It was also presumed that assay of renal antigens in urine and serum with the respective anti-human renal monoclonal antibodies could be a new tool in diagnosing renal diseases.     

Effects of extracorporeal shock wave lithotripsy on plasma levels of nitric oxide and cyclic nucleotides in human subjects

PURPOSE: The role of extracorporeal shock wave lithotripsy (ESWL, Dornier Medizintechnik GmbH, Wessling Munchen, Germany) on plasma nitric oxide (NO) and cyclic nucleotides was investigated. It is known that ESWL increased plasma levels of vasoactive substances. MATERIALS AND METHODS: A total of 28 patients undergoing ESWL for renal (14) and lower ureteral (14) stones participated in a prospective study. Peripheral blood samples were analyzed for plasma nitrite, NO metabolite, cyclic 3', 5'-guanosine monophosphate (cGMP), cyclic 3',5'-adenosine monophosphate and plasma renin activity before, immediately after, 30 and 60 minutes after ESWL. Urine samples were also analyzed for nitrite before, immediately after, 30 and 60 minutes after ESWL. Blood pressure and pulse rate were measured before and after ESWL. RESULTS: ESWL increased mean plasma nitrite levels. Before, immediately after, 30 and 60 minutes after ESWL mean plasma nitrate plus or minus standard error in patients with renal versus lower ureteral stones was 43.6 +/- 8.5, 52.8 +/- 7.4, 54.0 +/- 8.0 and 52.2 +/- 9.1 versus 27 +/- 5.8, 24.6 +/- 4.7, 23.6 +/- 4.8 and 28.0 +/- 7.1 nM., respectively. Before, immediately after, 30 and 60 minutes after ESWL mean plasma cGMP in patients with renal versus lower ureteral stones was 1.21 +/- 0.1, 1.64 +/- 0.16, 1.52 +/- 0.12 and 1.58 +/- 0.14 versus 1.45 +/- 0.18, 1.52 +/- 0.13, 1.52 +/- 0.15 and 1.51 +/- 0.11 fmol., respectively. Cyclic 3',5'-adenosine monophosphate was not increased by ESWL in patients with renal stones. Urine nitrite increased slightly but not significantly after ESWL. Plasma cyclic nucleotides and nitrite, and urine nitrite were not changed by ESWL in patients with lower ureteral stones. Plasma renin activity decreased significantly in patients with renal stones 60 minutes after ESWL. Blood pressure and pulse rates increased mildly without statistical significance after ESWL for renal stones. CONCLUSIONS: ESWL increases plasma nitrite and cGMP in patients with renal stones, suggesting that shock waves stimulate the NO-cGMP signaling pathway.     

The product of duration and amount of proteinuria (proteinuria index) is a possible marker for glomerular and tubulointerstitial damage in IgA nephropathy

BACKGROUND/AIMS: IgA nephropathy (IgAN) is one of the major causes for chronic renal failure (CRF). Presence of massive proteinuria, hypertension, increased serum creatinine level and sclerotic histopathological changes of the glomerulus are known to be determinants for the progression of CRF. However, the relationships between duration of proteinuria/hematuria and histopathological changes, which may be correlated with the renal prognosis, have not been clarified. METHODS: A cross-sectional, univariate analysis of clinical parameters on the four glomerular and three tubulointerstitial histopathological grades in 57 untreated biopsy-proven IgAN patients (M/F = 32/25) was performed. RESULTS: The age at the time of renal biopsy (35.2 +/- 13.0 years; mean +/- SD), average duration of proteinuria (5.3 +/- 5.8 years), mean urinary protein excretion (0.99 +/- 1.22 g/day), serum creatinine (Cr 0.97 +/- 0.28 mg/dl), Cr clearance (Ccr 75.5 +/- 29.4 ml/min), and blood urea nitrogen (BUN 15.4 +/- 3.9 mg/dl) were well correlated with both histopathological grades. The product of duration (years) and urinary protein excretion (g/day) at the time of renal biopsy was more significantly correlated with glomerular and tubulointerstitial histopathological grades and serum Cr. CONCLUSION: The natural course of IgAN is steadily progressive depending on the duration and amount of proteinuria. The product of these two factors (proteinuria index) may be a useful predictor for glomerular and interstitial histopathological changes and the fate of renal function in IgAN.     

Increased nitric oxide production during acute rejection in kidney transplantation: a useful marker to aid in the diagnosis of rejection

BACKGROUND: The diagnosis of acute rejection (AR) relies on biopsy (Bx), with all the noninvasive tests failing to show satisfactory predictive value. Nitric oxide (NO) has been shown to play a role in AR. The aim of this study is to analyze the relationship between NO and (1) biopsy-proven allograft rejection and (2) other reasons of allograft dysfunction. PATIENTS AND METHODS: Fifty consecutive renal allograft recipients ages 23-72 yrs who were transplanted were prospectively recruited. Blood samples were collected for 3 months. Endogenous serum nitrate (SNO(3)) levels were measured with Griess reagent in 1178 samples. Biopsies were performed as clinically indicated. Tacrolimus levels, urinary cultures, and renal function tests were done as per unit protocol. RESULTS: Fifty recipients (mean+/-SD age 45.2+/-2.18 yrs, 24 men and 6 women) underwent 68 biopsies. Forty-five Bx (66.2%) showed AR in 19 recipients (mean age 47+/-8) and 23 (33.8%) Bx in 13 recipients (mean age 43+/-12) showed no AR. SNO(3) in AR was (73+/-8.89 micromol/L) compared with negative Bx (45+/-4.5 micromol/L; P<0.05). There was also a significant difference in SNO(3) during AR and other causes of allograft dysfunction; delayed graft function (54+/-7.8 micromol/L), urinary tract infection (44+/-2.9 micromol/L), tacrolimus toxicity (51+/-2.86 micromol/L), and increase in serum creatinine (44+/-2.36 micromol/L). CONCLUSION: There is a significant increase of serum nitrate with episodes of acute rejection compared with other causes of renal dysfunction. SNO(3) can therefore aid in the diagnosis of acute rejection.     

Plasma amino acid profile and L-arginine uptake in red blood cells from malnourished uremic patients.

BACKGROUND: Patients with end-stage chronic renal failure (CRF) (uremia) have a high prevalence of inflammation, malnutrition, and oxidative stress. All of these features seem to be associated with the increased cardiovascular mortality observed in these patients. Nitric oxide (NO) is involved in the pathogenesis of CRF. The present study investigates the effects of nutritional status on L-arginine transport (NO precursor), plasma amino acid profile, and concentration of tumor necrosis factor (TNF)-alpha in uremic patients on hemodialysis (HD). METHODS: A total of 32 uremic patients on regular HD and 16 healthy controls were included in this study. Kinetic studies of L-arginine transport, mediated by cationic transport systems y(+) and y(+)L into red blood cells, plasma concentrations of amino acids (measured by high-performance liquid chromatography), and plasma TNF-alpha level (evaluated by enzyme-linked immunosorbent assay), were analyzed in malnourished and well-nourished patients (isolated by body mass index). RESULTS: L-arginine influx by system y(+) in red blood cells (micromol/L cells(-1)h(-1)) was increased in both malnourished (377 +/- 41) and well-nourished (461 +/- 63) patients with CRF compared with controls (287 +/- 28). Plasma levels of all cationic amino acids (L-arginine, L-ornithine, and L-lysine) were low in uremic patients compared with controls. Among the uremic population, the reduction in plasma cationic amino acids levels was greater in malnourished patients. L-cysteine and L-glutamate, precursors of glutathione, were dramatically increased in plasma from uremic patients, independently of nutritional status. In addition, TNF-alpha concentration in plasma was enhanced in malnourished uremic patients (3.4 +/- 0.7 pg/mL) compared with controls (1.2 +/- 0.1 pg/mL) and well-nourished patients (1.9 +/- 0.1 pg/mL). CONCLUSIONS: Our results suggest an increased catabolism of cationic amino acids, inflammatory markers, and oxidative stress in CRF, especially in malnourished patients. The reduced plasma concentration of plasma L-arginine is counterbalanced by enhanced rates of transport, resulting in an activation of NO synthesis in uremia.     

Natriuresis and blood pressure in patients with chronic renal failure following L-arginine infusion

Nitric oxide (NO) is known to be generated from L-arginine and may regulate glomerular filtration, tubular sodium reabsorption, and renin secretion. Impairment of renal function might influence NO production secondary to endothelial dysfunction, decreased NO synthesis and increased activity of arginine analogues inhibiting NO synthase. In this study, we evaluated the effect of L-arginine on the blood pressure and urinary sodium excretion in patients with chronic renal failure. A 300-ml dose of 10% L-arginine solution was administered intravenously over 30 min and blood pressure was monitored every 10 min under basal conditions and for 120 min after infusion. The patients were divided into two groups based on the reduction in mean blood pressure (dMBP) following infusion, namely non-responders (dMBP < 10 mmHg) and responders (dMBP > 10 mmHg). Urine and blood samples were collected to determine electrolytes, urinary NO2 + NO3 by the Griess method, urinary cGMP, plasma renin activity (PRA), and the plasma aldosterone concentration (PAC). L-arginine significantly decreased MBP in 8 patients and caused no significant change in 10 patients. Urinary sodium excretion and the NO2 + NO3 level were significantly increased following L-arginine infusion and the increment of fractional excretion of sodium was higher in responders. However, there were no significant changes in PRA, PAC, and cGMP. Our findings suggest that a vasodilator effect of NO induced by L-arginine loading may, at least in part, be associated with increased renal sodium excretion in patients with chronic renal failure.     

Urodilatin, not nitroprusside, combined with dopamine reverses ischemic acute renal failure.

The present study was undertaken to: (a) clarify the comparative renal potency of bolus injection of the natriuretic peptides urodilatin and ANF99-126 in the rat; (b) establish whether or not intravenous (i.v.) infusion of urodilatin (200 ng/min) combined with dopamine (UD) to maintain mean arterial pressure could improve GFR or renal histology in established experimental ischemic acute renal failure (ARF) induced by 30 minutes of bilateral renal artery clamping; (c) assess comparative efficacies of nitroprusside, an activator of soluble guanylate cyclase, combined with dopamine (ND) or control infusions of dopamine alone (DA), under equivalent conditions; and (d) determine effects of intra-renal arterial infusions of the stable cGMP analogue dibutyryl-cGMP immediately after renal artery clamping (RAC). After initial dose finding studies, i.v. infusion of UD 24 hours after 30 minutes of RAC improved GFR over five hours from 0.24 +/- 0.04 to 1.0 +/- 0.16 ml/min in association with a threefold rise in plasma cGMP and a 13-fold increase in urinary cGMP excretion. Plasma creatinine dropped by 41% from 230 +/- 16 to 135 +/- 18 microM/liter and was still reduced 24 hours later with values averaging 106 +/- 14 compared to 274 +/- 53 microM/liter in non-treated animals. During infusion, UV and FENa+ increased from 1.4 +/- 0.2 to 8.3 ml/min, and from 2.9 +/- 0.5 to maximum values of 15.8 +/- 2.4%. ND or DA alone were less effective, increasing GFR only to 14 and 20%, respectively, of normal values, but improvements were not sustained; in contrast to UD, ND did not alter plasma or urinary cGMP. In addition, DBcGMP was ineffective in improving GFR during early ARF. Histologically UD, but not ND, markedly reduced the incidence of granular casts, tubular desquamation and tubular necrosis in cortical areas and increased the incidence of medullary mitoses.     

Erythrocyte nitric oxide metabolism in patients with chronic renal failure.

AIMS: This study aims to investigate arginine-nitric oxide pathway in chronic renal failure (CRF) and to establish erythrocyte nitric oxide synthase (NOS) and arginase (ARG) activities in patients with CRF. MATERIALS AND METHODS: NOS and ARG activities were measured in erythrocytes from 30 patients with CRF and 12-control subjects. RESULTS: Erythrocyte NOS activity was found to be significantly lower and ARG activity higher in patients with CRF compared with controls. No differences were, however, found between patients with and without hemodialysis. A negative correlation (r = -0.7) was established between ARG and NOS activities in erythrocytes from patients. CONCLUSIONS: Results suggest that erythrocyte NO production is diminished in patients with CRF, possibly due to decreased NOS and increased ARG activities.     

Autocrine effects of nitric oxide on HCO(3)(-) transport by rat thick ascending limb

BACKGROUND: In vivo and in vitro studies have shown that nitric oxide (NO) is an important modulator of transport processes along the nephron. The thick ascending limb (TAL) plays a significant role in the urine-concentrating mechanism and in the maintenance of acid/base balance. METHODS: TALs from male Sprague-Dawley rats were isolated and perfused, and net bicarbonate flux (J(HCO3)(-) was determined. RESULTS: In perfused TALs, 0.5 mmol/L L-arginine (L-Arg), the substrate for NO synthase, significantly lowered J(HCO3)(-) from 35.4 +/- 4.6 to 23.2 +/- 2.9 pmol. mm(-1). min(-1), a decrease of 36.9 +/- 11.6% (P < 0.025). D-Arg (0.5 mmol/L) had no effect on J(HCO3)(-) (N = 7). In the presence of 5 mmol/L L-NAME, an NO synthase (NOS) inhibitor, the addition of L-Arg did not affect TAL J(HCO3)(-) (43.4 +/- 4.4 vs. 44.6 +/- 5.0 pmol. mm(-1). min(-1)). L-NAME alone (5 mmol/L) did not affect TAL J(HCO3)(-). After removing L-Arg from the bath, J(HCO3)(-) increased from 26.2 +/- 3.9 to 34.8 +/- 3.2 pmol. mm(-1). min(-1) (P < 0.01), indicating no cytotoxicity of NO. We next investigated the effect of cGMP analogues on TAL J(HCO3)(-). 8-Br-cGMP (50 micromol/L) and db-cGMP (50 micromol/L) significantly decreased J(HCO3)(-) by 26.3 +/- 9.1% and 35.1 +/- 11.6%, respectively. In the presence of cGMP (50 micromol/L), the addition of L-Arg had no effect on J(HCO3)(-). In the presence of KT-5823 (2 mircromol/L), a protein kinase G inhibitor, the addition of L-Arg did not change TAL J(HCO3)(-) (N = 5). CONCLUSIONS: We conclude that (1) endogenously produced NO inhibits TAL J(HCO3)(-) in an autocrine manner, (2) cGMP mediates all the effects of NO, and (3) this effect is mediated by protein kinase G activation.     

Supplementation with a low dose of L-arginine reduces blood pressure and endothelin-1 production in hypertensive uraemic rats.

BACKGROUND: We documented recently that increased endothelin-1 (ET-1) production in blood vessels and glomeruli of uraemic rats plays a crucial role in the development of hypertension and the progression of chronic renal failure. Normally, biological effects and local production of ET-1 are attenuated by the immediate release of nitric oxide (NO). Increasing evidence suggest, however, that NO release is impaired in chronic renal failure. We investigated whether supplementation with L-arginine, the natural precursor of NO, improves NO synthesis in uraemic rats with reduced renal mass and modulates vascular and renal ET-1 production as well as blood pressure and renal failure progression. METHODS: One week after surgical renal mass reduction, the uraemic and sham-operated animals received either no treatment or 0.1% L-arginine in drinking water for 5 weeks. In another series of experiments, uraemic rats received 1% L-arginine for 5 weeks. Immunoreactive-ET-1 (ir-ET-1) levels in plasma, urine, and vascular and renal tissue preparations was measured by radioimmunoassay after sample extraction and purification. RESULTS: Before treatment, systolic blood pressure was significantly elevated in uraemic animals compared to sham-operated controls (156+/-7 vs 111+/-3 mmHg, respectively; P<0.01). Thereafter, systolic blood pressure increased further in uraemic-untreated rats (systolic blood pressure at week 5; 199+/-9 mmHg, P<0.01), whereas it remained similar in uraemic rats supplemented with 0.1% L-arginine (171+/-9 mmHg, NS). At the end of the study, serum creatinine and urea, proteinuria and ir-ET-1 excretion were significantly augmented, while creatinine clearance was reduced in uraemic animals compared to the controls. Ir-ET-1 level was also increased in glomeruli as well as in thoracic aorta, mesenteric arterial bed, and pre-glomerular arteries, and was associated with vascular hypertrophy as assessed by tissue weight. In contrast, ir-ET-1 level was diminished in the renal papilla of uraemic rats. Treatment with 0.1% L-arginine significantly reduced proteinuria and urinary ir-ET-1 excretion (P<0.05) as well as ir-ET-1 level in glomeruli (P<0.01) and in thoracic aorta (P<0.05). These changes were associated with increased plasma NO metabolites NO2/NO3 levels in L-arginine-treated animals (P<0.01) and reduced aortic hypertrophy (P<0.05). In contrast, supplementation with 1% L-arginine had no effect on systolic blood pressure in uraemic rats, but exacerbated proteinuria and urinary ir-ET-1 excretion and increased serum urea (P<0.05) were observed. CONCLUSIONS: These results indicate that improvement of NO release with a low dose but not with a high dose of L-arginine significantly attenuates the development of hypertension and the progression of renal insufficiency in rats with reduced renal mass. These protective effects may be mediated in part by the reduction of vascular and renal ET-1 production.     

The influence of acute renal injury on arginine and methylarginines metabolism

Abstract

Arginine (ARG) and its methylated analogs (methylarginines) are the crucial regulators of nitric oxide (NO) bioavailability. ARG is the substrate for NO synthesis, whereas monomethylarginine (MMA) and asymmetric dimethylarginine (ADMA) are potent inhibitors. Symmetric dimethylarginine (SDMA) does not interfere with NO synthesis, but competes with ARG for the intracellular transport. The kidneys play the major role in ARG and methylarginines metabolism. They synthesize ARG de novo and eliminate methylarginines by excretion into urine and also by enzyme dimethylarginine dimethylaminohydrolase (DDAH) degrading only ADMA and MMA. Acute renal injury (ARI) is known to be accompanied by reduced NO production in the body. This study aimed to investigate the influence of ARI on ARG and methylarginines metabolism, and to establish the relationship between disturbances in the latter and reduced NO bioavailability in ARI. The rhabdomyolysis-related ARI model in rats was used. ARI reduced renal synthesis of ARG and its level in circulation as well as renal DDAH activity. However, ADMA did not accumulate because of its increased urinary excretion. Whole-body production of SDMA was increased significantly, whereas whole-body metabolism of MMA did not change. ARG and methylarginines content in renal tissue was decreased. Moreover, the balance between the substrate and inhibitors for NO synthesis was changed in favor of the inhibitors in renal tissue as well as in blood, and daily urinary excretion of NO metabolites was significantly decreased. Thus, ARI provokes severe disturbances in ARG and methylarginines metabolism that results in reduced NO bioavailability in the kidney and the whole body.     

Vasopeptidase inhibitor restores the balance of vasoactive hormones in progressive nephropathy

BACKGROUND: The mechanism(s) underlying greater renoprotection of combined blockade of angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) by vasopeptidase over ACE inhibitors are ill defined. We previously found that progressive renal disease is associated with increased renal synthesis of endothelin-1 (ET-1) in the face of reduced generation of renal nitric oxide (NO) in the remnant kidney model. Here we compared changes in urinary excretion of ET-1 and nitrite/nitrate, markers of renal ET-1, and NO synthesis, respectively, and urinary cGMP, an indirect index of renal atrial natriuretic peptide (ANP) synthesis, after administration of vasopeptidase or ACE inhibitor in rats with renal mass reduction (RMR). METHODS: Twenty-one days after 5/6 nephrectomy, after the onset of hypertension and overt proteinuria, rats were divided in 3 groups (N= 7-8) and given daily by gavage: vehicle, the vasopeptidase inhibitor AVE7688 (3 mg/kg bid), or enalapril (5 mg/kg bid) until day 90. Normal rats (N= 5) served as control rats. RESULTS: Systolic blood pressure in RMR rats was equally controlled by AVE7688 and enalapril. AVE7688 resulted in a significant antiproteinuric effect, with urinary protein levels being reduced on average by 83% in respect to vehicle (88 +/- 28 vs. 518 +/- 27 mg/day, P < 0.0001). Enalapril achieved a 47% reduction in proteinuria (277 +/- 81 mg/day, P < 0.01 vs. vehicle) to levels that remained higher (P < 0.01), however, than those after AVE7688. Renal function impairment and glomerular and tubular changes were significantly (P < 0.05 vs. vehicle) ameliorated by AVE7688, and partially affected by enalapril. AVE7688 reduced the abnormal urinary excretion of ET-1 of RMR animals (98 +/- 8 vs. vehicle: 302 +/- 50 pg/24 h, P < 0.001) more than enalapril (159 +/- 14 pg/24 h, P < 0.05 vs. AVE7688). Consistently, AVE7688 was more effective than enalapril in augmenting renal synthesis of NO (2487 +/- 267 and 1519 +/- 217 vs. vehicle: 678 +/- 71 nmol/15 h; P < 0.001, AVE7688 vs. vehicle, P < 0.01 AVE7688 vs. enalapril). AVE7688 significantly increased urinary cGMP (78 +/- 6 vs. vehicle 45 +/- 9 nmol/24 h; P < 0.01). CONCLUSION: The superior renoprotection achieved by AVE7688 over enalapril in progressive renal injury is due to the correction of the altered balance of vasoconstrictor/vasodilator mediators in the kidney.     

Asymmetrical dimethylarginine plasma concentrations are related to basal nitric oxide release but not endothelium-dependent vasodilation of resistance arteries in peritoneal dialysis patients

Vascular dysfunction in chronic renal failure may be linked to reduced nitric oxide (NO) bioactivity and increased circulating concentrations of the endogenous NO synthase inhibitor asymmetrical dimethyl L-arginine (ADMA). The association between ADMA and basal endothelial NO release and endothelium-dependent vasodilation in resistance arteries of chronic renal failure patients is unknown. Forearm blood flow responses to the endothelium-dependent vasodilator acetylcholine, the endothelium-independent vasodilator nitroglycerine, and the endothelium-dependent vasoconstrictor N(G)-monomethyl-L-arginine (L-NMMA) were assessed in 37 peritoneal dialysis patients. L-arginine and ADMA plasma concentrations were measured by HPLC. ADMA (mean +/- SEM: 0.68 +/- 0.02 micromol/L) was associated with basal forearm blood flow (r = -0.33; P < 0.05) and L-NMMA induced vasoconstriction (r = -0.55; P < 0.0005), but not with dilator effects of acetylcholine or nitroglycerine. L-arginine (68 +/- 3 micromol/L) tended to correlate with acetylcholine-induced vasodilation (r = 0.32; P = 0.05) but was not associated with other parameters. ADMA is related to basal but not to acetylcholine-stimulated NO bioactivity in patients on peritoneal dialysis. Impaired endothelium-dependent vasodilation found in chronic renal failure is not explained by elevated circulating NO synthase inhibitors in renal failure.