L-arginine reduces tubular cell injury in acute post-ischaemic renal failure.

BACKGROUND: The pathophysiology of renal ischaemia, resulting in tubular cell injury and leading to acute renal failure (ARF), remains unclear. An ever-increasing number of investigations focus on a possible role of nitric oxide (NO) in regulating circulation during ARF. In this context, we investigated the influence of chronic stimulation or inhibition of NO synthesis, or both, on haemodynamic parameters, histology and plasma renin activity (PRA) after ischaemia-reperfusion injury of rat kidneys. METHODS: Experiments were performed on adult, male Wistar rats. Before induction of ARF, a group of animals was treated with a NO synthesis inhibitor (L-NAME) and another group was treated with a precursor of NO synthesis (L-arginine). The animals received those substances for 4 weeks. Control groups received the same amount of tap water for 4 or 8 weeks and were divided into groups with ARF (4 weeks--ARF group and 8 weeks ARF group) and a sham-operated group. Another group of rats was treated first with L-NAME and then with L-arginine in their drinking water, for 4 weeks for each of these two substances. All parameters were evaluated 24 h after the induction of ischaemic ARF or the sham operation. RESULTS: Our results show that such long-term stimulation of NO release by L-arginine improved renal haemodynamics in the ischaemic form of ARF. Renal blood flow (RBF) increased by 96% in the L-arginine-treated rats with ARF compared with the group with ARF alone. Inhibition of NO synthesis worsens renal haemodynamics after ARF. However, this aggravation can be reversed by L-arginine. The rate of water reabsorption was reduced in all groups with ARF, but this reduction was least in the group treated with L-arginine. The rate of Na+ reabsorption was reduced in all groups 24 h after renal ischaemia, but a significant decrease was observed after the inhibition of NO synthesis. Histological examination of the kidney specimens showed that morphological changes were least in the rats treated with L-arginine, when compared with all other groups with ARF. Nevertheless, the lesions were most prominent in the L-NAME+ARF group. In this group, the areas of corticomedullar necrosis were more widespread in comparison with other groups, especially the L-arginine group where only swelling of the proximal tubular cells was observed. Treatment with L-NAME was not accompanied by any significant alteration in the plasma concentration of angiotensin I (ANG I), while in the group treated with L-arginine ANG I had a tendency to decrease. CONCLUSIONS: Acute post-ischaemic renal failure may be alleviated by administering the NO substrate (L-arginine). NO acts cytoprotectively on tubular epithelial cells in ischaemia--reperfusion injury of rat kidney. Evidence of this comes from both histopathological findings and increased tubular water and sodium reabsorption. However, inhibition of NO synthesis (provoked by L-NAME) worsens renal haemodynamics and aggravates morphological changes after ARF. These aggravations can, however, be reversed by L-arginine.     

Dietary arginine supplementation attenuates renal damage after relief of unilateral ureteral obstruction in rats

BACKGROUND: Progression of renal injury after relief of unilateral ureteral obstruction (UUO) has been demonstrated. Nitric oxide (NO) may be an effective intervention due to its vasodilatory, antifibrotic, and anti-apoptotic effects. Herein, we used dietary L-arginine (ARG) supplementation in a UUO relief model. METHODS: This study comprised group 1, control (no treatment). All other rats were subject to 3-day UUO, which was then relieved, and the rats maintained for 7 additional days. Group 2, no additional treatment; group 3, L-ARG; group 4, L-NAME, NO synthase inhibitor; group 5, ARG and L-NAME. Urinary NO(2/3) was quantified. GFR and ERPF were measured at day 10. Interstitial fibrosis and fibroblast expression, macrophage infiltration, tubular apoptosis, and proliferation, NOS expression, and the levels of tissue TGF-beta were evaluated. RESULTS: Urinary NO(2/3) was significantly increased by ARG treatment and decreased by L-NAME. GFR and ERPF measured 7 days following relief were not significantly different in the previously obstructed kidneys (POK) of groups 2 and 3. L-NAME significantly reduced GFR and ERPF in the POK. ARG significantly reduced apoptosis, macrophage infiltration, and fibroblast expression in the POK. L-NAME exacerbated the effects on apoptosis and fibroblasts. Fibrosis was minimal in groups 1 through 3, but was significantly increased by L-NAME. ARG did not affect renal NOS expression and tissue TGF-beta1 levels. CONCLUSION: Dietary ARG supplementation during UUO relief did not improve ERPF or GFR. However, renal damage, including fibrosis, apoptosis, and macrophage infiltration was significantly improved by ARG treatment. This suggests that increasing NO availability could be beneficial in the setting of UUO relief.     

Endothelium-dependent vasodilatation produced by the L-arginine/nitric oxide pathway in normal and ischemic bone

We used an experimental model of the perfused isolated rabbit tibia to investigate the vasodilatation produced by nitric oxide in the circulation of bone. Tibiae were perfused at a constant flow rate while the perfusion pressure was monitored continuously. Perfusion pressure was raised by the addition of noradrenaline to the perfusate, and dose responses were measured for bolus doses of acetylcholine and sodium nitroprusside. N^w-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthesis, was then added to the perfusate at a concentration of 10⁴ M, and the dose responses to acetylcholine and sodium nitroprusside were repeated. Measurements were performed on groups of bones after 0, 6, 12, and 24 hours of normothermic ischemia (n 5,4,6, and 9, respectively). Both acetylcholine and sodium nitroprusside produced significant vasodilatation after 0 and 6 hours' ischemia, but no significant response was observed after 12 or 24 hours of ischemia. The vasodilatation produced by acetylcholine was significantly attenuated when L-NAME was added to the perfusate, but the vasodilatation produced by sodium nitroprusside remained unchanged. These findings confirm endothelial production of NO by stimulation of muscarinic receptors on the endothelial cells in bone and indicate that vasodilatation via the L-arginine/NO pathway remains viable for 6 hours after normothermic ischemia.     

Paradoxical increase in nitric oxide synthase activity in hypercholesterolaemic rats with impaired renal function and decreased activity of nitric oxide.

BACKGROUND: We have shown that acute exposure of oxidized low-density lipoprotein (OX-LDL) induces vasoconstriction in renal vessels and reduces glomerular filtration rate (GFR) in an isolated perfused rat kidney model by decreasing the activity of nitric oxide (NO). L-arginine has a protective role against OX-LDl-induced vasoconstriction. Micropuncture studies have demonstrated that short-term diet-induced hypercholesterolaemia is associated with decreased GFR and renal blood flow and increased glomerular capillary pressure. This may be mediated by decreased activity of NO. METHODS: Rats were made hypercholesterolaemic by supplementing the standard chow with 4% cholesterol and 1% sodium cholate. A group of rats on hypercholesterolaemic diet also received L-arginine in the drinking water. After 4 and 6 weeks, blood samples and 24-h urine samples were collected for the measurement of biochemical parameters. After 6 weeks, all rats were subjected to isolated perfusion of kidneys at a constant pressure of 100 mmHg. During isolated perfusion, the unused contralateral kidney was taken for morphological studies and for assessing the activity of nitric oxide synthase enzyme by beta-NADPH diaphorase histochemistry. RESULTS: Rats fed a high-cholesterol diet had LDL levels 3-6 times greater than the rats fed standard chow. Rats that received L-arginine in the drinking water had serum L-arginine levels 5-6 times greater than control rats. At 6 weeks, creatinine clearance was significantly lower in the rats on the high-cholesterol diet compared to the rats on standard chow and rats on high-cholesterol diet plus L-arginine. Twenty-four-hour urinary total nitrate and nitrite excretion in the hypercholesterolaemic rats was 1.5-2 times greater than that of control rats. Twenty-four-hour urinary cGMP excretion was significantly lower in the rats on a high-cholesterol diet, but in the rats on high-cholesterol diet and L-arginine, 24-h urinary cGMP excretion was not significantly different from that of control rats. During isolated perfusion of kidneys, renal perfusate flow was found to be significantly reduced in the kidneys taken from the rats on a high-fat diet compared to controls. L-arginine supplementation in the drinking water almost completely reversed the effect of a high-fat diet. Inulin clearance was also significantly reduced in kidneys on a high-fat diet in contrast to controls but not in kidneys on high fat-diet and L-arginine. Basal cGMP excretion in urine was significantly lower in the kidneys taken from the rats on a high-fat diet compared to controls. L-arginine supplementation restored the basal cGMP excretion in these kidneys. NO synthase (NOS) enzyme activity as assessed by NADPH diaphorase activity showed that kidney sections taken from the rats on a high-fat diet showed more intense staining, indicating increased activity compared to the kidney sections taken from the rats on a normal diet. CONCLUSION: Though activity of NO is diminished in hypercholesterolaemic rats with impaired renal function, there is a paradoxical increase in NO production and NOS activity. L-arginine reverses the effects of a high-fat diet.     

HAIR DYE POISONING—A CASE

Gentamicin (GM) often causes polyuric acute renal failure (ARF) in humans and animals. GM-mediated ARF in rats was accompanied with activated renin—angiotensin system, increased renal endothelin content, and enhanced lipid per oxidation. Suppression of the renin-angiotensin activity by desoxycorticosterone acetate and saline drinking, and treatment with superoxide dismutase attenuated the GM-induced decline in whole-kidney GFR with well-maintained RBF but did not reduce the severity of tubular necrosis. On the other hand, treatment with dimethylthiourea, a hydroxyl radical scavenger, attenuated the GM-mediated decline in GFR and lessened tubular necrosis but did not ameliorate the reduction in RBF. These duta suggest contributions of both vascular and tubular factors to the GM-induced decline in GFR in rats. However, relative importance of these factors probably differs with different doses of the agent.     

L-arginine deficiency and supplementation in experimental acute renal failure and in human kidney transplantation

BACKGROUND: The "L-arginine paradox" refers to situations where L-arginine (L-Arg) supplementation stimulates nitric oxide (NO) synthesis, despite saturating intracellular concentrations. This paradox is frequently observed in acute renal failure (ARF). First, the effects of L-Arg on renal function of rats with ARF were studied. Based on the promising results from these initial studies, the second part of our study searched for a form of ARF in humans that could be studied easily under conditions with little variance and yet was linked with endothelial dysfunction. Thus, we investigated the effects of L-Arg supplementation immediately after kidney transplantation in 54 patients. METHODS: In uranyl nitrate-induced ARF in rats the effects of L-Arg and L-NNA (inhibitor of nitric oxide synthase; NOS) on glomerular filtration rate (GFR), renal plasma flow (RPF), blood pressure (BP) and NOx (NO2- +NO3-) excretion were examined. Tissue L-Arg levels, NOS activities, immunodetection of NOS and superoxide dismutase (SOD), activities of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and xanthine oxidase, and nitrotyrosine immunoreactive protein (NT-IR) were determined and compared to sham operated animals. Secondly, in a randomized, double-blind study, the effects of L-Arg on GFR and RPF were investigated in 54 kidney transplant recipients, receiving IV L-Arg for three days. GFR and RPF were measured on days 1, 3, 5 and 10 by scintigraphy. RESULTS: In experimental ARF, decreased RPF and GFR were associated with reduced tissue L-Arg levels, endothelial NOS-III expression, NO formation and NOx excretion. Reduction in GFR, RPF and NOx excretion were reversed upon administration of exogenous L-Arg. There also was a loss of Cu,Zn-SOD, a key enzyme against oxidative stress, and an elevation of NT-IR, an indicator of nitrosative stress and suggested marker for pathological actions of NO. However, NT-IR was not dependent on de novo NO synthesis and not related to the functional effects of l-Arg administration. In kidney transplant recipients receiving organs with a short cold ischemia time (CIT) and from young donors, that is, those with a higher likelihood of a functional endothelium, early administration of L-Arg improved renal function. CONCLUSION: Both experimental and clinical data show that \L-Arg deficiency and endothelial dysfunction are pathomechanistically relevant in ARF. The data suggest a therapeutic potential for the administration of L-Arg in ARF and kidney transplantation, at least in patients receiving kidneys with shorter CIT and from younger donors.     

Effect of glycine on medullary thick ascending limb injury in perfused kidneys

The addition of 2 mM glycine to the recirculating perfusate of isolated perfused rat kidneys almost completely prevented the severe morphological injury to tubular cells lining the medullary thick ascending limb (mTAL) that normally develops in this preparation. Glycine was similarly effective in reducing mTAL injury associated with hypoxic perfusion, indomethacin and amphotericin. Fractional reabsorption of sodium was increased with glycine, without any change in perfusate flow to the whole kidney and without consistent improvement in GFR. L-alanine demonstrated a similar though less pronounced cytoprotective action, but glutamine, cysteine, glutamate, cysteine plus glutamate, 1-serine and 4-aminoisobutyric acid all had little or no effect in preventing severe mTAL injury. The protective effect of glycine was unimpaired by the arginine analogue NG-monomethyl-l-arginine (L-NMMA), suggesting that the endothelial-derived relaxing factor, NO, was not involved. The action of glycine was not reduced by the addition of a substrate (benzoate) or a product (hippurate) of the glycine N-acyltransferase reaction. Glycine did not depress the respiration of dispersed mTALs prepared from rat kidneys. The cytoprotective effect of glycine in the mTAL of perfused kidneys, shared with l-alanine, appears to be relatively specific for these amino acids and probably unrelated to a diminution in cell work.     

Renal effects of HMG-CoA reductase inhibition in a rat model of chronic inhibition of nitric oxide synthesis

BACKGROUND/AIMS: In addition to their lipid-lowering effects, HMG-CoA reductase inhibitors (statins) induce a variety of pleiotropic actions that have been recently studied in the area of cardiovascular and renal protection. In the present studies we sought to determine whether statins retain beneficial effects in the experimental model of NO deficiency achieved by chronic administration of a pressor dose of L-arginine analogue N-nitro-L-arginine-methyl ester (L-NAME). METHODS: To address this issue, blood pressure (BP), renal function (GFR), and albuminuria were determined in rats treated for 4 weeks with L-NAME, L-NAME + atorvastatin (ATO), and in untreated controls. In addition, renal cortical protein expression of caveolin 1 (CAV1), vascular endothelial growth factor (VEGF), and activity of RhoA were also determined. RESULTS: L-NAME administration resulted in sustained elevation of BP, decreased GFR, and in higher albuminuria as compared to control animals. Co-administration of ATO with L-NAME normalized albuminuria and prevented decreases in GFR in L-NAME rats without having an impact on pressor effects of L-NAME. CAV1 protein expression was similar in all groups of rats. In contrast, VEGF expression and RhoA activity was increased in L-NAME-treated animals, and normalized with co-administration of ATO. CONCLUSION: Treatment with ATO exerts early nephroprotective effects in the NO-deficient model of hypertension. These effects could be mediated by amelioration of VEGF expression and reduction of RhoA activity.     

Effects of selective iNOS inhibition in sepsis: evaluation of lung tissue damage and blood gases

NO is an important mediator in the generalized inflammatory response of the body during sepsis and septic shock. We investigated the possible effects of L-arginine and aminoguanidine on plasma NO levels and the interaction between NO levels and lung tissue damage and blood gases in sepsis. Fifty Wistar male rats were used in this study and divided into five groups: group 1, sham group; group 2, CLP (sepsis); group 3, CLP + 10 mg/kg L-arginine administration; group 4, CLP +15 mg/kg aminoguanidine administration; group 5: CLP + L-arginine + aminoguanidine given in similar doses. Sepsis was induced by cecal ligation and puncture (CLP) method. Drugs were administered at postoperative hours 4 and 12. The levels in the aminoguanidine and aminoguanidine + L-arginine groups were similar to the sham group. Lung tissue damage in the sepsis and L-arginine groups was more severe than the other groups.     

Nitric oxide in flow-through venous flaps and effects of L-arginine and nitro-L-arginine methyl ester (L-NAME) on nitric oxide and flap survival in rabbits

OBJECT: Venous flaps are relatively recent practices in plastic surgery, and their life mechanisms are not known exactly. Partial necroses frequently occur in these flaps; therefore, their survival should be enhanced. Nitric oxide (NO) is an endogenous compound which has recently been dwelt upon frequently in flap pathophysiology, and its effect on viability in conventional flaps has been demonstrated. However, its role in venous flaps is unknown. The purpose of this study is to determine possible changes in the NO level in venous flaps and to investigate the possible effects of NO synthesis precursor and inhibitor on the venous flap NO level and flap survival. MATERIAL AND METHODS: Thirty white male rabbits of New Zealand type, aged 6 months, were divided into 3 groups as control (n = 10), L-arginine (n = 10), and nitro-L-arginine methyl ester (L-NAME) (n = 10). Blood and tissue samples were taken from one ear of 10 rabbits in the control group for the determination of NO basal levels 2 weeks before flap practice. The 3-x-5-cm flow-through venous flaps, which are sitting on the anterior branch of the central vein, were elevated on each ear of 10 rabbits in all groups. After flaps were sutured to their beds, 2 mL/d saline, 1 g/kg/d L-arginine (NO synthesis precursor), and 50 mg/kg/d L-NAME (NO synthesis inhibitor) were administered intraperitoneally in control, L-arginine, and L-NAME groups, respectively, for 3 days. At the 24th postoperative hour, blood and tissue samples were taken from all animals for biochemical analyses. At day 7, flap survivals were assessed. RESULTS: Mean NO levels in the blood following the flap elevation (129 +/- 76 micromol/mg protein) increased in comparison with basal levels (59 +/- 44 micromol/mg protein) (P < 0.06); however, the tissue level remained unchanged. NO levels in the blood in the L-arginine and L-NAME groups were alike compared with the control group. The tissue NO level in L-NAME group (0.08 +/- 0.03 micromol/mg protein) decreased significantly compared to the control group (0.46 +/- 0.36 micromol/mg protein) (P < 0.001). Mean flap survival in the L-arginine group (95% +/- 6) increased according to the control group (61% +/- 14) (P < 0.001), whereas it did not change in the L-NAME group (55% +/- 13). CONCLUSION: In our model of venous flap, NO level in the blood increased, while it did not change in the tissue; L-arginine significantly enhanced flap viability without affecting NO level. Additionally, L-NAME decreased NO level, but it did not affect flap survival. In light of these findings, NO increases in venous flaps; the change in its level does not affect flap survival, though. However, L-arginine enhances venous flap survival if not by virtue of NO.     

L-Arginine given after ischaemic preconditioning can enhance cardioprotection in isolated rat hearts.

OBJECTIVE: Ischaemic or pharmacological preconditioning with L-arginine has been reported to be insufficient for optimal cardioprotection. The ability of nitric oxide (NO) to enhance ischaemic preconditioning was assessed, and the role of L-arginine-induced ischaemic preconditioning in myocardial protection was determined. METHODS: Isolated rat hearts were prepared and divided into six groups: control hearts (control, n=6) were perfused without global ischaemia at 37 degrees C for 160 min; global ischaemia hearts (GI, n=6) were subjected to ischaemia for 20 min and reperfusion for 120 min; ischaemic preconditioned hearts (IP, n=6) received 2 min of zero-flow global ischaemia followed by 5 min reperfusion, before 20 min of global ischaemia; L-arginine hearts (ARG, n=6) received 1 mmol/l L-arginine for 5 min, before 20 min of global ischaemia; ischaemic preconditioning plus nitro-L-arginine methyl ester hearts (IP+L-NAME, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 3 mmol/l L-NAME in Krebs-Henseleit buffer, before 20 min of global ischaemia; and ischaemic preconditioning plus L-arginine hearts (IP+ARG, n=6) received 2 min of ischaemic preconditioning and 5 min reperfusion with 1 mmol/l L-arginine in Krebs-Henseleit buffer. Haemodynamic parameters and coronary flow were recorded continuously. Nitrites and nitrates (NOx) were measured 5 and 60 min after reperfusion, and infarct size was also determined. RESULTS: In the IP+ARG group, significant amelioration and preservation of left ventricular peak developed pressure and coronary flow was observed compared with the GI, IP, ARG and IP+L-NAME groups. Infarct size in the IP+ARG group was reduced significantly compared with that in the GI, IP, ARG and IP+L-NAME groups. Significant preservation of NOx was observed during reperfusion in the IP+ARG group compared with the GI group. CONCLUSIONS: Inhibition of NO synthase with L-NAME had little impact on ischaemic preconditioning, suggesting that endogenous NO is not a major mediator of ischaemic preconditioning. Nevertheless, enhancement of the effects of ischaemic preconditioning can be achieved with L-arginine, a precursor of NO, improving post-ischaemic functional recovery and infarct size in the isolated rat heart.     

The role of nitric oxide pathway in the renal ischemia-reperfusion injury in rats

INTRODUCTION: Nitric oxide (NO), synthesized from L-arginine by the enzyme nitric oxide synthase (NOS), seems to play an ambiguous role during tissue ischemia-reperfusion injury. Our objective was to evaluate the effects of L-arginine, a NO donor, and N(G)-nitro-L-arginine-methylester (L-NAME), a NOS inhibitor, on oxidative stress, renal dysfunction, histologic alterations and surgical mortality rate induced by renal ischemia-reperfusion (RIR) in uninephrectomized rats. MATERIALS AND METHODS: One-hundred and ninety-seven Wistar rats were randomized into five experimental groups. Group 1: sham operation; group 2: right uninephrectomy (UNI); group 3: UNI + RIR in the contralateral kidney; group 4: UNI + L-NAME (20 mg/kg; intraperitoneally) + RIR; and group 5: UNI + L-arginine + RIR. The effect of the drugs was evaluated by lipid peroxidation measured by the renal malondialdehyde (MD) content and chemiluminescence (CL) levels, serum creatinine (Cr) levels, urinary volume, tubular necrosis and athrophy, inflammatory infiltrate, interstitial fibrosis as histologic evaluation and surgical mortality rate after the procedures. A P value less than 0.05 was considered significant. RESULTS: Right uninephrectomy did not alter the renal parameters. RIR increased Cr levels (at 24 and 96 h of reperfusion), index of lipid peroxidation (both MD and QL levels), and worsened the histologic aspects. Pretreatment with L-arginine reduced the kidney levels of QL when compared with the non-treated group (5574 +/- 909 vs. 13 660 +/- 1104 cps/mg of protein; P < 0.05) but increased the MD levels (0.97 +/- 0.24 vs. 0.79 +/- 0.06 nmol/mg of protein; P < 0.05). Moreover, L-arginine attenuated the increment of Cr levels, inflammatory infiltrate and tubular athrophy in rats subjected to RIR (P < 0.05). On the other hand, pretreatment with L-NAME increased both CL (17 482 +/- 4397 vs. 13 660 +/- 1104 cps/mg of protein; P < 0.05) and MD levels (1.16 +/- 0.11 vs. 0.79 +/- 0.06 nmol/mg of protein; P < 0.05). Furthermore, L-NAME worsened the renal dysfunction (P < 0.05) at 192 h after the RIR, and surgical mortality rates were similar (P > 0.05). CONCLUSION: L-arginine has a tendency to exert a beneficial effect on renal damage during RIR in rats. Moreover, L-NAME seems to worsen the renal damage by increasing the kidney-levels of CL and impairment of renal function probably due to reduction of NO production.     

Endogenous nitric oxide and exogenous nitric oxide supplementation in hepatic ischemia-reperfusion injury in the rat

BACKGROUND: Although nitric oxide (NO) is thought to be beneficial in hepatic ischemia-reperfusion (I/R), the mechanisms for this effect are not well established. METHODS: To investigate the effects of endogenous NO and exogenous NO supplementation on hepatic I/R injury and their pathogenic mechanisms, serum ALT and hyaluronic acid (endothelial cell damage), and hepatic malondialdehyde and H2O2 (oxidative stress), myeloperoxidase activity (leukocyte accumulation), and endothelin (vasoconstrictor peptide opposite to NO) were determined at different reperfusion periods in untreated rats and rats receiving L-NAME, L-NAME+L-arginine, and spermine NONOate (exogenous NO donor). RESULTS: After reperfusion every parameter increased in untreated animals. Endogenous NO synthesis inhibition by L-NAME increased hepatocyte and endothelial damage as compared to untreated rats, which was reverted and even improved by the addition of L-arginine. Spermine NONOate also improved this damage. However, different mechanisms account for the beneficial effect of endogenous and exogenous NO. Oxidative stress decreased by both L-NAME and L-NAME+L-arginine, but remained unmodified by spermine NONOate. Myeloperoxidase increased by L-NAME and this effect was reverted by the addition of L-arginine, whereas no change was observed with spermine NONOate. Endothelin levels were not modified by L-NAME and L-NAME+L-arginine, but decreased with spermine NONOate. CONCLUSIONS: These results suggest that, although both endogenous and exogenous NO exert a protective role in experimental hepatic I/R injury, the mechanisms of the beneficial effect of the two sources of NO are different.     

Grass carp (Ctenopharyngodon idellus) bile may inhibit the release of renal dipeptidase from the proximal tubules by nitric oxide generation

There are many reports on acute renal failure (ARF) after ingestion of grass carp bile (CB; Ctenopharyngodon idellus). Renal dipeptidase (RDPase; EC 3.4.13.19) is a glycosylphosphatidylinositol-anchored ectoenzyme within the renal proximal tubules (PTs) and is proposed as a diagnostic enzyme of renal disease. We examined the release of RDPase following treatment with CB and various nitric oxide (NO) related compounds in porcine PTs. The RDPase release from PTs was inhibited by CB in a concentration-dependent manner and was also inhibited by sodium nitroprusside (direct NO donor) and L-arginine (NO synthase substrate) in the tested range (0-12 mM). CB-treated (0. 1 mg/ml) PTs showed a decreased RDPase activity in comparison with the control group. This inhibition was blocked by 2 mM L-NAME (NO synthase inhibitor) and U73122 (inhibitor of phosphatidylinositol-specific phospholipase C) in a concentration-dependent manner. Eel bile (0-0.1 mg/ml), used as the control, did not significantly affect the RDPase release from PTs. The NO concentration was observed as nitrite, the degradation product of the NO metabolism, increased in proportion to CB and L-arginine. The increase of nitrite to 151.5% by CB treatment (0.1 mg/ml) was blocked by 2 mM L-NAME (95.5%). When the phospholipase C pathway was blocked by 10 and 20 microM U73122, the nitrite generation decreased to 122.7 and 89.4%, respectively. These results strongly suggest that NO generation and the phospholipase C pathway affect the RDPase release from the PTs and that they may be involved in the development of ARF in vivo following CB ingestion. The release of RDPase from PTs could be a useful tool not only for this CB-caused ARF, but also for the elucidation of other biochemical mechanisms.     

Nitric oxide and thromboxane A2-mediated pulmonary microvascular dysfunction

OBJECTIVES: To examine whether the lung releases nitric oxide (NO) in response to thromboxane A2 and to examine the local release of NO as a protective compensatory mechanism by which the lung responds to the proinflammatory and vasoactive effects of thromboxane A2. DESIGN: The lungs of anesthetized Sprague-Dawley rats were perfused in vitro with Krebs-Henseleit buffer that contained an inhibitor of NO synthase (nitroglycerinenitro-L-arginine methyl ester [L-NAME]) (10(-4) mol/L), an NO donor (sodium nitroprusside) (10(-8) mol/L), or perfusate alone. Following equilibration, the thromboxane A2 receptor agonist 9,11-dideoxy-11alpha, 9alpha-epoxymethanoprostaglandin F2alpha(U-46619) (7.1 X 10(-8) mol/L) was added to the perfusate. Fifteen minutes later, the capillary filtration coefficient, pulmonary arterial pressure, and vascular resistance were measured. Pulmonary NO release was assessed by quantitating the release of cyclic guanosine monophosphate into the perfusate. RESULTS: The capillary filtration coefficient of lungs exposed to U-46619 was 3.5 times greater than that of lungs perfused with buffer alone (P<.05). The addition of sodium nitroprusside reduced the increase in capillary filtration coefficient associated with U-46619 by 50% (P<.05) whereas L-NAME had no effect. The addition of U-46619 to the perfused lung caused a 3.0+/-0.4 mm Hg increase in pulmonary artery pressure (P<.01) with a corresponding rise in total vascular resistance (P<.05). This effect was exacerbated by L-NAME (P<.05) and inhibited by sodium nitroprusside (P<.05). Exposure of the isolated lungs to U-46619 caused a 4-fold increase in cyclic guanosine monophosphate levels within the perfusate. CONCLUSION: These data are consistent with the hypothesis that NO release may be an important protective mechanism by which the lung responds to thromboxane A2.     

Endotoxin-induced acute renal failure in rats: effects of L-arginine and nitric oxide synthase inhibition on renal function

BACKGROUND: The regulation of renal hemodynamics is closely related to the L-arginine (L-Arg)/nitric oxide (NO) pathway. NO - metabolized from L-Arg - is capable of improving renal function in ischemic and toxic acute renal failure (ARF), while NO synthase (NOS) inhibition induces deterioration in renal function. The mortality rate in patients with septic shock is increased when treated with a non-selective NOS inhibitor, while the incidence of ARF requiring renal replacement therapy is unaffected. To date, there are no studies on the impact of NOS substrate (L-Arg) and inhibitor (L-NMMA) on renal function in early lipopolysaccharide (LPS)-induced ARF. METHODS: ARF was induced by intravenous (i.v.) LPS. Animals were treated with L-Arg, L-NMMA (NOS substrate and inhibitor), a combination of both or saline. Glomerular filtration rate (GFR), urine flow, fractional sodium excretion, excretion of NO metabolism stable end products and blood pressure (BP) were recorded at baseline, after ARF induction, during drug infusion and thereafter. RESULTS: L-Arg induced better GFR during infusion. Excretion of the NO metabolism end products was highest in the L-Arg group and lowest in the NOS inhibitor group. L-Arg administration had no influence on BP, while L-NMMA induced a slight elevation. CONCLUSIONS: We conclude that exogenous L-Arg exerts beneficial effects in early LPS-induced ARF in rats during drug infusion, while NOS inhibition has no influence on GFR. Subcellular compartmentalization of the L-Arg pool in cytoplasma and the rapid utilization of exogenous L-Arg in such a micro-environment could explain this effect, which has been observed in other ARF models and was called the "L-Arg paradox". In further studies the effects of early and prolonged administration of L-Arg in endotoxinemia should be investigated.     

A model of hypoxic renal failure

Models of ischemic acute renal failure (ARF) must consider the combination of tissue hypoxia, insufficient nutrient flow, and anaerobic waste product accumulation. This study utilized isolated perfused rat kidneys to characterize the renal response to a graded hypoxic insult while maintaining flow. Kidneys were perfused at 37 degrees C with an asanguineous Krebs-buffered saline. After a 40-min baseline period, 10 or 30 min of hypoxia was rapidly achieved by reducing perfusate oxygen tension from approximately 550 to 50 mm Hg. Ten minutes of hypoxia resulted in tubular dysfunction evidenced by a 50% increase in urine flow (UV) and a 10% decrease in percent sodium reabsorption (%Na). Glomerular filtration rate (GFR) decreased by 40% during 10 min of hypoxia and returned to control levels after reoxygenation. Thirty minutes of hypoxia caused an irreversible 85% decrease in GFR accompanied by a 50% decrease in UV. This insult also caused more severe tubular dysfunction evidenced by a 20% decrease in %Na and a 35% decrease in oxygen consumption. These results demonstrate a spectrum of renal dysfunction that corresponds to the clinical spectrum from nonoliguric to oliguric ARF. This model of hypoxic ARF allows more specific investigation into the hypoxic component of postischemic renal dysfunction.     

Reduction of the drug-induced nephrotoxicity by ATP-MgCl2. 1. Effects on the cis-Diamminedichloroplatinum-treated isolated perfused kidneys

cis-Diamminedichloroplatinum (CDDP), a widely used cancer chemotherapeutic agent, has been shown to cause dose-dependent acute renal failure (ARF) probably secondary to a direct nephrotoxic effect on proximal tubule cells. The aim of this study was to determine whether administration of ATP-MgCl₂ could ameliorate the deleterious effects of CDDP. Isolated rat kidneys were perfused for 2 hr with a 3.5 g % dextran T-110-Krebs HCO₃ solution containing 100 μg/ml of CDDP. [³H]Inulin was added to measure GFR. Trace amounts of ¹⁴C-methylated cytochrome c (cyt) were added to the perfusate to determine the protein reabsorptive capacity (a sensitive indicator of tubular damage) of isolated perfused rat kidneys. Cyt, inulin radioactivity, and [Na⁺] were measured in the perfusate and urine in control and CDDP-treated kidneys. In additional experiments, ATP-MgCl₂ was added simultaneously (0.3 mM) or 1 hr (2 mM) after CDDP treatment. The results indicate that after 2 hr of perfusion, CDDP treatment led to a marked inhibition of protein reabsorption with only a minimal decrease in Na⁺ and H₂O absorption. Furthermore, GFR was not significantly altered despite a marked diuresis. Post-treatment with ATP-MgCl₂ led to partial alleviation of the nephrotoxic effect of CDDP after 1 hr of perfusion. ATP-MgCl₂ treatment simultaneously with CDDP, however, fully protected the protein reabsorptive capacity of CDDP-treated kidneys. The potential for administering ATP-MgCl₂ simultaneously with CDDP suggests a new therapeutic modality in preventing ARF due to CDDP therapy.     

Role of the L-arginine/nitric oxide pathway in renal ischaemia-reperfusion in rats.

OBJECTIVE: To study the role of the L-arginine/nitric oxide (NO) pathway during renal ischaemia-reperfusion in rats. DESIGN: Randomised experimental study. SETTING: Teaching hospital, Brazil. ANIMALS: 97 male Wistar rats randomly assigned to 4 groups for the assessment of renal dysfunction and to 6 groups for the assessment of the oxidative stress induced on renal cell membranes by ischaemia-reperfusion. INTERVENTIONS: The animals underwent sham-operation or renal ischaemia-reperfusion (n = 9 each) with or without pretreatment with L-arginine (a NO donor) or L-NAME (N(omega)-nitro-L-arginine methyl ester--an inhibitor of NO production) (n = 10 each). MAIN OUTCOME MEASURES: Serum creatinine concentrations and oxidative stress by chemiluminescence initiated by the tert-butyl hydroperoxide technique. RESULTS: Renal ischaemia-reperfusion significantly worsened renal dysfunction and increased oxidative stress in the ischaemia-reperfusion group after 24 and 96 hours of reperfusion compared with the control group (p < 0.05). Pretreatment with L-NAME slightly but not significantly increased serum creatinine concentrations after 24 and 96 hours of reperfusion together with activity of reactive oxygen species during renal ischaemia-reperfusion. L-arginine also significantly protected renal function and reduced the increment in the amount of chemiluminescence induced by giving L-NAME during 24 and 96 hours of reperfusion (p < 0.05). CONCLUSION: The L-arginine/NO pathway seems to have a slightly protective effect on the kidney after renal ischaemia-reperfusion injury in rats. These results need to be confirmed by studies in human beings.     

Amelioration of gentamicin nephrotoxicity by green tea extract in uninephrectomized rats as a model of progressive renal failure

Rationale: Gentamicin (GM) is an effective antibiotic against severe infection but has limitations related to nephrotoxicity. This study investigates whether green tea extract (GTE), an antioxidant, could ameliorate the nephrotoxic effect of GM in uninephrectomized rats. Objectives: The right kidneys of 40 rats were surgically removed and 1 week later the animals were divided into four groups (n = 10). Group 1 served as control, Group 2 as GTE group, Group 3 as GM group, and Group 4 as GM+GTE group. Kidney function, inflammatory cytokine TNF-α, oxidant and antioxidant parameters of renal tissue, as well as histopathological studies were assessed. Main findings: Injecting uninephrectomized rats with GM induced renal dysfunction as shown by significant elevations in serum creatinine and urea. Serum TNF-α and oxidative stress parameters (superoxide anion and lipid peroxides) were also significantly increased. On the contrary, antioxidative parameters [superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH)] were significantly decreased. Histopathological examination of renal tissue illustrated features of degeneration, marked cellular infiltration, tubular dilatation, and varying degrees of necrosis. GTE given to GM rats reduced these nephrotoxicity parameters. Serum creatinine, urea, and TNF-α were almost normalized in the GM+GTE group. The oxidative stress parameters were significantly decreased and the antioxidative parameters were significantly increased. Conclusion: GTE ameliorates GM-induced nephrotoxicity and oxidative damage by improving antioxidant defense and tissue integrity. Further human studies are necessary to demonstrate the antioxidant effects of GTE on renal diseases. Nevertheless, green tea (GT) may offer an inexpensive, nontoxic, and effective intervention strategy in subjects with a risk for GM-induced nephrotoxicity.