Role of nitric oxide in renal tubular apoptosis of unilateral ureteral obstruction

BACKGROUND: The obstructed kidney in unilateral ureteral obstruction (UUO) is characterized by renal atrophy and tissue loss, which is mediated by renal tubular apoptosis. We sought to determine whether NO is involved in renal tubular apoptosis in vitro and in vivo. METHODS: Rat renal tubular epithelial cells (NRK-52E) were subjected to mechanical stretch, and apoptosis and cell size were analyzed by flow cytometry. Furthermore, we studied UUO in mice lacking the gene for inducible nitric oxide synthase (iNOS-/-) and their wild-type littermates. Tubular apoptosis and proliferation were detected by immunostaining. NOS activity and NOS expression were assessed by a citrulline assay and Western blot, respectively. RESULTS: Stretching-induced apoptosis in NRK-52E, which was reduced when NO was increased; conversely, stretch-induced apoptosis was increased when a NOS inhibitor was added to the cells. Stretched cells are larger and more apoptotic than unstretched cells. In UUO, the obstructed kidney of iNOS-/- mice exhibited more apoptotic renal tubules than the wild-type mice through 14 days of UUO. The obstructed kidney of iNOS-/- mice at day 3 showed more proliferative tubules compared with wild type. The obstructed kidney of wild-type mice exhibited higher total NOS activity until day 7 after UUO compared with iNOS-/- mice. However, the obstructed kidney of day 14 wild-type mice exhibited significantly lower iNOS activity and protein compared with the day 0 kidney. CONCLUSION: These results suggest that mechanical stretch is related to renal tubular apoptosis and that NO plays a protective role in this system in UUO.     

Pro- and anti-fibrotic effects of vascular endothelial growth factor in chronic kidney diseases

Renal fibrosis is the inevitable common end-point of all progressive chronic kidney diseases. The underlying mechanisms of renal fibrosis are complex, and currently there is no effective therapy against renal fibrosis. Renal microvascular rarefaction contributes to the progression of renal fibrosis; however, an imbalance between proangiogenic and antiangiogenic factors leads to the loss of renal microvasculature. Vascular endothelial growth factor (VEGF) is the most important pro-angiogenic factor. Recent studies have unraveled the involvement of VEGF in the regulation of renal microvascular rarefaction and fibrosis via various mechanisms; however, it is not clear whether it has anti-fibrotic or pro-fibrotic effect. This paper reviews the available evidence pertaining to the function of VEGF in the fibrotic process and explores the associated underlying mechanisms. Our synthesis will help identify the future research priorities for developing specialized treatments for alleviating or preventing renal fibrosis. Abbreviation: VEGF: vascular endothelial growth factor; CKD: chronic kidney disease; ESKD: end-stage kidney disease; ER: endoplasmic reticulum; VEGFR: vascular endothelial growth factor receptor; AKI: acute kidney injury; EMT: epithelial-to-mesenchymal transition; HIF: hypoxia-inducible factor; α-SMA: α smooth muscle actin; UUO: unilateral ureteral obstruction; TGF-β: transforming growth factor-β; PMT: pericyte-myofibroblast transition; NO: nitric oxide; NOS: nitric oxide synthase; nNOS: neuronal nitric oxide synthase; iNOS: inducible nitric oxide synthase; eNOS: endothelial nitric oxide synthase; sGC: soluble guanylate cyclase; PKG: soluble guanylate cyclase dependent protein kinases; UP R: unfolded protein response     

诱导型一氧化氮合酶在单侧输尿管梗阻大鼠肾脏的表达

目的:探讨诱导型一氧化氮合酶(iNOS)在单侧输尿管梗阻(UUO)大鼠术侧肾脏的表达.方法:建立左侧输尿管梗阻模型(UUO组),设假手术组为对照.3 d后应用逆转录-聚合酶链反应(RT-PCR)检测iNOS的mRNA水平.结果:与对照组相比,UUO组大鼠肾脏出现明显病理变化,并且其iNOS mRNA表达明显增加.结论:iNOS参与UUO的发生和发展的病理过程.     

Inhibition of nitric oxide synthase reduces renal ischemia/reperfusion injury

BACKGROUND: The role of nitric oxide (NO) production because of inducible nitric oxide synthase (iNOS) in the pathogenesis of renal ischemia/reperfusion (I/R) injury is unclear. In this study the roles of both iNOS and NO were characterized in a rat model of renal I/R injury. In addition, the effect of iNOS inhibition on renal function was evaluated. METHODS: Sprague-Dawley rats underwent 45 min of left renal ischemia and contralateral nephrectomy followed by various periods of reperfusion and renal function analysis [plasma creatinine, fractional excretion of sodium (FENa), creatinine clearance (CrCl), and measurement of plasma and urine NO levels]. In addition, the effect of treatment with 1400W, a highly selective iNOS inhibitor, was evaluated. RESULTS: Renal dysfunction peaked at 48 h after reperfusion and immunohistochemistry studies revealed iNOS expression in the vasculature (3 h) and renal tubules (48 h) after reperfusion. Renal function improved significantly in treated animals compared to controls [creatinine of 1.1 v. 1.9 mg/dl (P < 0.05) and CrCl of 0.54 v. 0.31 ml/min (P < 0.05), respectively]. In addition, FENa was decreased by 50%, plasma NO levels were significantly lower (32.7 v. 45.7 micromol/L, P < 0.01), and deposition of nitrotyosine in the tubules of treated rats was less than in control animals. CONCLUSIONS: These data support the hypothesis that iNOS and NO are involved in the pathogenesis of renal I/R injury and suggests that use of iNOS inhibitors may be a valuable therapeutic strategy clinical situations where renal I/R may be prevalent.     

Changes in nitric oxide production in the rat kidney due to CaOx nephrolithiasis

AIMS: The aim of the study was to test the hypothesis that the renal nitric oxide (NO) system is involved in the animal model of nephrolithiasis by evaluating the relationship between nitric oxide synthase (NOS) and oxidative stress. METHODS: Deposition of renal calculi was induced by adding 0.75% ethylene glycol (EG) to the drinking water of male Wistar rats. After 42 days of treatment, urinary biochemistry and urinary levels of oxalate, NO metabolites (nitrate and nitrite), cGMP, and lipid peroxides, and markers for renal damage and oxidative stress in the kidney were examined. In the second part of the experiment, two diuretic stimuli (intrarenal infusion of l-arginine or saline loading) were applied to test the renal NO system response. Finally, levels of three isoforms of NOS in renal tissues were evaluated by immunostaining. RESULTS: In the EG-treated rats, increased urinary excretion of enzymes and lipid peroxides and increased nitrotyrosine levels and oxidative injury markers in the kidneys indicated that peroxynitrite formation occurred during oxidative stress, while the 24-hr urinary excretion of NO metabolites and cGMP remained unchanged. In contrast to control rats, urinary excretion and NO metabolites and cGMP excretion were unresponsive to intrarenal l-arginine infusion; in response to saline loading, an increase in these factors was seen, but the increase was only 50% of that seen in the identically treated control group. A significant decrease in eNOS expression and increase in iNOS expression were observed in the renal medulla of the EG-treated group, whereas expression of nNOS was not affected. CONCLUSIONS: Although basal renal NO production remained unchanged, excessive peroxynitrite formation in the kidney was noted in this model. A decreased response of the NOS system was noted when diuretic stimuli were applied. How the imbalance between eNOS and iNOS expression influences CaOx stone formation requires detailed evaluation.     

黄芪当归合剂对单侧输尿管梗阻大鼠肾脏血管活性物质变化的影响

目的 本研究通过观察黄芪当归合剂(A&A)对单侧输尿管梗阻(UUO)模型肾组织血管紧张素Ⅱ(Ang-Ⅱ)、内皮素-1(ET-1)、一氧化氮(NO)水平及一氧化氮合酶(NOS)的影响，以进一步揭示A&A抑制肾纤维化机制。方法 Wistar大鼠随机分为假手术(Sham)、UUO和UAA(UUO+A&A)组，造模后0、3、7、10 d分析各组肾脏中NO、Ang-Ⅱ、ET-1水平和NOS活性及3种NOS的表达。结果 (1)造模后UUO组的Ang-Ⅱ和ET-1水平持续增高；A&A仅在第3天时降低Ang-Ⅱ水平(P < 0.05)。(2)造模后UUO组的NO浓度在第10天时才明显增高；而UAA组中NO浓度逐渐增高，第3天时明显高于UUO组(P < 0.05)。(3)UUO组内皮型eNOS在髓质血管内表达增高，且UAA组与UUO组间没有显著性差异。第3天时UAA组神经型nNOS表达低于UUO组(P < 0.05)。UAA组cNOS的活性明显高于Sham和UUO组。诱导型iNOS表达和活性3组间差异均无统计学意义。结论 梗阻性肾病中，A&A在早期降低肾内Ang-Ⅱ水平、且持续增强eNOS活性使NO产生增加，从而可能降低血管张力、改善肾脏的缺血及缺氧状态，减轻肾间质纤维化。     

Renal amino acid metabolism during endotoxemia in the rat

BACKGROUND: The kidney has an important function in the exchange of nitrogenous metabolites. Glutamine is the most important substrate for renal ammoniagenesis and thus plays a crucial role in acid-base homeostasis. Furthermore, the kidney is the main endogenous source for de novo arginine production from citrulline, which in turn is derived from intestinal glutamine metabolism. Sepsis is a condition in which glutamine availability is reduced, whereas the need for arginine biosynthesis may be increased. Limited bioavailability of glutamine may affect arginine synthesis, which may have consequences for nitric oxide (NO) synthesis. Therefore, we studied renal glutamine and arginine metabolism in a rat model of endotoxemia and related this to NO metabolism. MATERIALS AND METHODS: Rats were subject to double hit endotoxemia, and control rats received 0.9% NaCl. Renal blood flow was measured using para-aminohippuric acid. Concentrations of plasma amino acids and nitrate were measured in the aorta and renal vein to calculate net renal uptake or release of amino acids and address NO production. RESULTS: The arterial concentrations of glutamine and ammonia were not changed in endotoxemic rats. Although renal glutamine uptake was reduced, total renal ammonia production was not changed during endotoxemia. The arterial concentration of citrulline and renal citrulline uptake was not altered in endotoxin-treated rats, but renal arginine production was increased. However, no effect was observed on nitric oxide production. CONCLUSIONS: Although the kidney has very important functions in the excretion of waste products and in interorgan metabolism, this study suggests that the kidney has a limited role in glutamine, arginine, and NO metabolism during late endotoxemia in rats.     

Adenoviral gene transfer of endothelial nitric oxide synthase (eNOS) to the penis improves age-related erectile dysfunction in the rat

Nitric oxide (NO) is the principal mediator of penile erection. NO is synthesized by a variety of nitric oxide synthases (NOS). It has been demonstrated that a decrease in NOS activity, as observed in aging, is associated with a diminished erectile response. The objective of this study was to determine if adenoviral-mediated gene transfer of eNOS could reverse age-related erectile dysfunction in the rat. Two groups of animals were transfected with adenoviruses: (1) aged rats (60 weeks) with AdRSVbetagal; and (2) aged rats (60 weeks) with AdRSVeNOS. Five days after transfection, these study animals underwent cavernosal nerve stimulation (CNS) to assess erectile function and their responses were compared with young (20 weeks) control rats. Cross-sections of the rat penises transfected with AdRSVeNOS were examined after trichrome staining. Adenoviral transduction efficiency of beta-galactosidase reporter gene was measured by a galacto-light chemiluminescent reporter gene assay in cavernosal tissues of rats administered AdRSVbetagal. The transgene expression of eNOS was examined by RT-PCR in rats transfected with AdRSVbetagal and AdRSVeNOS. eNOS and iNOS protein levels were measured by Western blot analysis, and cGMP levels were assessed in cavernosal tissue by enzyme immunoassay. Adenoviral expression of the beta-galactosidase reporter gene was observed in cavernosal tissue for up to 30 days, with peak expression registered at 5 days after intracavernosal administration of AdRSVbetagal. Cross-sections of the rat penises transfected with the AdRSVeNOS revealed no pathological (morphological or histological) changes. Five days after administration of AdRSVeNOS, eNOS protein, mRNA and cGMP levels in the corpora cavernosa were significantly increased (P<0. 05), while iNOS protein levels remained unchanged (P>0.05). In conclusion, enhanced expression of eNOS employing an adenoviral vector significantly increased the erectile response to cavernosal nerve stimulation in the aged rat, similar to the response observed in younger rats. These data suggest that in vivo adenoviral gene transfer of eNOS can physiologically improve erectile function in the aged rat.     

Antibody to transforming growth factor-beta ameliorates tubular apoptosis in unilateral ureteral obstruction

BACKGROUND: Unilateral ureteral obstruction (UUO) is characterized by progressive renal atrophy, renal interstitial fibrosis, an increase in renal transforming growth factor-beta (TGF-beta), and renal tubular apoptosis. The present study was undertaken to determine the effect of a monoclonal antibody to TGF-beta (1D11) in UUO. METHODS: Mechanical stretch was applied to tubular epithelial cells (NRK-52E) by a computer-assisted system. Three doses of 1D11 (either 0.5, 2, or 4 mg/rat) were administered to rats one day prior to UUO and every two days thereafter, and kidneys were harvested at day 13. Fibrosis was assessed by measuring tissue hydroxyproline and mRNA for collagen and fibronectin. Apoptosis was assessed with the terminal deoxy transferase uridine triphosphate nick end-labeling assay. TGF-beta levels were determined by bioassay. Western blot and immunostaining were used to identify proliferating cell nuclear antigen (PCNA), p53, bcl-2, and inducible nitric oxide synthase (iNOS). RESULTS: Stretch significantly induced apoptosis in NRK-52E cells, which was accompanied by an increased release of TGF-beta; 1D11 (10 microg/mL) totally inhibited stretch-induced apoptosis. Control obstructed kidney contained 20-fold higher TGF-beta as compared with its unobstructed kidney; 1D11 neutralized tissue TGF-beta of the obstructed kidney. Control obstructed kidney exhibited significantly more fibrosis and tubular apoptosis than its unobstructed counterpart, which was blunted by 1D11. In contrast, 1D11 significantly increased tubular proliferation. p53 immunostaining was localized to renal tubular nuclei of control obstructed kidney and was diminished by 1D11. In contrast, bcl-2 was up-regulated in the 1D11-treated obstructed kidney. Total NOS activity and iNOS activity of the obstructed kidney were increased by 1D11 treatment. CONCLUSION: The present study strongly suggests that an antibody to TGF-beta is a promising agent to prevent renal tubular fibrosis and apoptosis in UUO.     

Endogenous renal nitric oxide metabolism following experimental infrarenal aortic cross-clamp-induced ischaemia-reperfusion injury.

BACKGROUND: Abdominal aortic surgery is associated with marked changes in renal haemodynamics. The aim of this study was to investigate the influence of infrarenal cross-clamping on glomerular filtration rate and endogenous renal nitric oxide metabolism. METHODS: Groups of male Wistar rats were subjected to infrarenal aortic cross-clamping followed by reperfusion. Animals were allowed to recover after a left nephrectomy. The glomerular filtration rate of the remaining kidney was measured on the second and seventh day after the procedure before the animal was killed and the remaining kidney harvested. Total nitric oxide synthase (NOS) activity and expression of inducible NOS (iNOS) was determined in renal tissue following 1 h and 7 days of reperfusion. RESULTS: Glomerular filtration rate was impaired on the second and seventh day after operation in all animals subjected to lower torso ischaemia compared with controls (P < 0.05). Renal NOS activity was increased at 1 h and 7 days in animals subjected to infrarenal cross-clamping compared to controls (P < 0.01). iNOS was detected in renal tissue of animals subjected to infrarenal aortic cross-clamping on the seventh day after operation. CONCLUSION: Infrarenal aortic cross-clamping is associated with impairment of renal function in the early postoperative period. There is an increase in endogenous renal nitric oxide metabolism with iNOS expression. Presented in part to the Surgical Research Society, Dublin, Ireland, July 1998     

Down-regulation of inducible nitric oxide synthase (iNOS) in rat with congenital hydronephrosis

BACKGROUND: Most of our knowledge concerning obstructive uropathy has been derived mainly from surgically manipulated animal models, and the pathogenesis of congenital obstructive hydronephrosis is not fully elucidated. Nitric oxide (NO) acts as an important biological modulator with diverse physiological functions, which can be either toxic or protective depending on the situation. NO is synthesized from l-arginine by nitric oxide synthase, and in the kidney iNOS is expressed spontaneously. The aim of our study is to investigate the expression of iNOS protein and its relationship with tubulointerstitial fibrosis and tubular cell apoptosis in congenital hydronephrosis. METHODS: We conducted histological studies on 18 kidneys of six-week-old-rats from an inbred colony of congenital hydronephrosis with reference to the histological grading of the affected kidney, tubulointerstitial fibrosis, renal tubular atrophy, and tubular cell apoptosis. Renal transforming growth factor-beta1 (TGF-beta1) level was determined by a sandwich ELISA assay and the expression of iNOS was analyzed by western blotting. RESULTS: Most of the hydronephrotic kidneys were markedly enlarged with dilatation of the collecting system, parenchymal thinning, tubular atrophy, interstitial infiltration and fibrosis. Renal TGF-beta1 level was higher in hydronephrotic kidneys than normal control kidneys (364.81 +/- 52.60 vs. 221.19 +/- 22.53 pg/mg protein, P < 0.05). Tubular apoptotic score in hydronephrotic kidneys was also significantly higher than in the normal control kidneys (1.97 +/- 0.42 vs. 0.14 +/- 0.02/HPF, P < 0.01). The expression of iNOS protein was lower in the affected kidneys compared with the normal control kidneys (8.79 +/- 0.78 vs. 14.00 +/- 0.83 arbitrary unit, P < 0.01). There was a negative correlation between iNOS expression and histological grading in congenital hydronephrosis. The iNOS expression also correlated negatively with renal interstitial fibrosis, TGF-beta1 level and tubular cell apoptosis. CONCLUSION: Our study confirmed the down-regulation of iNOS expression in affected kidneys from rats with congenital hydronephrosis, in which the cytoprotective effect of NO may be lost or weakened.     

上调肾组织intermedin表达抑制单侧输尿管梗阻大鼠肾间质纤维化

目的观察上调肾组织intermedin(IMD)表达对单侧输尿管梗阻(UUO)大鼠肾间质纤维化的影响。 方法健康雄性Wistar大鼠随机分为假手术组、UUO组、IMD＋UUO组、空质粒＋UUO组。IMD＋UUO组和空质粒＋UUO组在输尿管结扎前分别将IMD-pcDNA3.1真核表达质粒和空质粒转入肾组织,real-time RT-PCR及免疫组化法检测转染效率。各组分别于术后7 d、14 d留取梗阻侧肾组织。HE、Masson染色观察肾组织病理变化;real-time RT-PCR检测肾组织中转化生长因子-β1(TGF-β1)、纤连蛋白(Fn1)的mRNA表达;Western印迹法检测Fn1的蛋白表达;免疫组化法检测TGF-β1的蛋白表达。 结果与假手术组相比,UUO组肾脏出现明显的病理改变,肾间质纤维化程度随梗阻时间延长加重(与假手术组比较,7 d, t＝11.927,P＝0.0003;14 d, t＝8.891,P＝0.0009);IMD＋UUO组肾脏病理改变及肾间质纤维化程度较同时间点UUO组明显减轻(7 d, t＝3.892,P＝0.018;14 d, t＝4.047,P＝0.016),而空质粒＋UUO组与UUO组无显著差别(7 d, t＝0.562,P＝0.604;14 d, t＝0.035,P＝0.974)。与同时间点假手术组相比,UUO组TGF-β1、Fn1的表达明显升高(TGF-β1 mRNA水平7 d, t＝4.432,P＝0.011;14 d, t＝4.873,P＝0.006;蛋白质水平7 d, t＝5.312,P＝0.006;14 d, t＝4.482,P＝0.011;Fn1 mRNA水平7 d, t＝6.053,P＝0.004;14 d, t＝7.345,P＝0.002;蛋白质水平7 d, t＝8.791,P＝0.009;14 d t＝8.027,P＝0.001);转染IMD质粒后Fn1的表达较同时间点UUO组明显下降(mRNA水平7 d, t＝3.103,P＝0.036;14 d, t＝2.913,P＝0.044;蛋白质水平7 d, t＝2.955,P＝0.042;14 d, t＝2.991,P＝0.040);而转染空质粒后Fn1的表达无明显变化(mRNA水平7 d, t＝0.095,P＝0.929;14 d, t＝0.158,P＝0.882;蛋白质水平7 d, t＝0.159,P＝0.881;14 d, t＝0.170,P＝0.874)。转染IMD和空质粒对TGF-β1的表达均无明显影响(转染IMD质粒mRNA水平7 d, t＝0.176,P＝0.869;14 d, t＝0.126,P＝0.906;蛋白质水平7 d, t＝0.198,P＝0.853;14 d, t＝0.196,P＝0.854;转染空质粒mRNA水平7 d, t＝0.100,P＝0.925;14 d, t＝0.097,P＝0.928;蛋白质水平7 d, t＝0.042,P＝0.968; 14 d, t＝0.060,P＝0.955)。 结论上调肾组织IMD的表达能明显减轻肾间质纤维化,但其作用不是通过直接抑制TGF-β1的表达实现的。     

Endotoxemic renal failure in mice: Role of tumor necrosis factor independent of inducible nitric oxide synthase

BACKGROUND: Renal failure is a frequent complication of sepsis with a high mortality. Tumor necrosis factor (TNF) has been suggested to be a factor in the acute renal failure in sepsis or endotoxemia. Recent studies also suggest involvement of nitric oxide (NO), generated by inducible NO synthase (iNOS), in the pathogenesis of endotoxin-induced renal failure. The present study tested the hypothesis that the role of TNF in endotoxic renal failure is mediated by iNOS-derived NO. METHODS: Renal function was evaluated in endotoxemic [Escherichia coli lipopolysaccharide (LPS), 5 mg/kg IP] wild-type and iNOS knockout mice. The effect of TNF neutralization on renal function during endotoxemia in mice was assessed by a TNF-soluble receptor (TNFsRp55). RESULTS: An injection of LPS to wild-type mice resulted in a 70% decrease in glomerular filtration rate (GFR) and in a 40% reduction in renal plasma flow (RPF) 16 hours after the injection. The results occurred independent of hypotension, morphological changes, apoptosis, and leukocyte accumulation. In mice pretreated with TNFsRp55, only a 30% decrease in GFR without a significant change in RPF in response to LPS, as compared with vehicle-treated mice, was observed. Also, the serum NO concentration was significantly lower in endotoxemic wild-type mice pretreated with TNFsRp55, as compared with untreated endotoxemic wild-type mice (260 +/- 52 vs. 673 +/- 112 micromol/L, P < 0.01). In LPS-injected iNOS knockout mice and wild-type mice treated with a selective iNOS inhibitor, 1400W, the development of renal failure was similar to that in wild-type mice. As in wild-type mice, TNFsRp55 significantly attenuated the decrease in GFR (a 33% decline, as compared with 75% without TNFsRp55) without a significant change in RPF in iNOS knockout mice given LPS. CONCLUSIONS: These results demonstrate a role of TNF in the early renal dysfunction (16 h) in a septic mouse model independent of iNOS, hypotension, apoptosis, leukocyte accumulation, and morphological alterations, thus suggesting renal hypoperfusion secondary to an imbalance between, as yet to be defined, renal vasoconstrictors and vasodilators.     

Attenuation of reperfusion injury by renal ischaemic preconditioning: the role of nitric oxide

OBJECTIVE: To determine the effect on nitric oxide (NO) release and renal NO synthase (endothelial, eNOS and inducible, iNOS) activity of renal ischaemia-reperfusion (I/R) in vivo in an animal model, and to examine the possible involvement of NO in ischaemic preconditioning (IP) of the kidney. MATERIALS AND METHODS: In a right-nephrectomized rat model, 42 animals were randomized in four groups: controls; IP-only (4 min of ischaemia followed by 11 min of reperfusion, total of four cycles); renal warm ischaemia (45 min) and 6 h reperfusion; ischaemia (45 min) preceded by IP pretreatment. Serum NO metabolites were assayed 2 and 6 h after ischaemia or the control equivalent. NOS expression in the kidney was detected immuno-histochemically, and damage assessed morphologically in sections stained with haematoxylin and eosin. Kidney function was assessed by the levels of serum creatinine, urea and electrolytes. RESULTS: Compared with before ischaemia, the concentration of serum NO metabolites at 6 h was increased in the IP-only animals (P = 0. 016) and in the IP + I/R group (P = 0.002). There was greater eNOS expression in the IP-only group (P = 0.009) and in the IP + I/R group than in controls (P = 0.050). iNOS expression was greater in the IP-only animals than in the control group (P = 0.050). Histological assessment showed less evidence of cellular damage in IP + I/R animals than in the I/R-alone group (P = 0.020). Serum creatinine level was not significantly different between the IP-only group and the control. There were no differences after 2 h of reperfusion. CONCLUSION: Ischaemic preconditioning has a protective effect on renal structure and function, which may be produced by increased NO release arising from increased NOS expression by 6 h after reperfusion.     

Chronic diabetic nephropathy: role of inducible nitric oxide synthase

Nitric oxide (NO) is a multifunctional mediator that has been implicated in the short-term hemodynamic alterations that occur in acute streptozocin (STZ)-induced diabetes. We investigated the role of NO produced by inducible nitric oxide synthase (iNOS) in chronic STZ diabetic nephropathy. Diabetes was induced in C57BL/6 and iNOS knockout (KO) mice with two intraperitoneal injections of STZ, 100 mg/kg. Animals were maintained without insulin treatment for 40 weeks. There were no significant differences between the strains in blood urea nitrogen (BUN), serum creatinine or glucose concentration, or urinary protein excretion during the entire observation period. Urinary nitrite + nitrate excretion was significantly lower in iNOS KO mice compared to control animals at all time points; in C57 mice, urinary nitrite declined progressively with more prolonged duration of diabetes. Renal hypertrophy (kidney weight/body weight) was noted in both strains of mice. However, histopathological assessment of renal tissue specimens at 16 and 40 weeks demonstrated increased mesangial hypercellularity and expansion as well as more prominent tubulointerstitial fibrosis in iNOS KO versus C57 mice. These changes were accompanied by increased interstitial deposition of type I collagen at 16 and 40 weeks in iNOS KO mice. Glomerular basement membrane staining for type IV collagen was also increased at 40 weeks in diabetic iNOS KO mice. While iNOS protein was undetectable in any of the kidney specimens obtained from either strain, eNOS was present throughout the course of chronic STZ diabetes. Moreover, eNOS expression was significantly increased by approximately 40% at 16 and 40 weeks of observation in iNOS KO versus C57 mice. There was no difference in renal cortical malondialdehyde content between the strains early or late in the disease course. In time control animals, there was no evidence of renal histopathological damage in iNOS KO or C57 mice after 40 weeks. We conclude that iNOS-derived NO modulates glomerulosclerosis and tubulointerstitial fibrosis in chronic STZ nephropathy. This action is probably a result of the direct actions of NO on the synthesis and degradation of extracellular matrix proteins. Received: 28 February 2001 / Revised: 10 August 2001 / Accepted: 13 August 2001