MO625INHIBITION OF SGLT-2 CANNOT RESCUE NEPHRIN EXPRESSION IN DIABETIC NEPHROPATHY

Background and Aims

Early glomerular damage in diabetes is induced by high blood glucose level (hyperglycemia) which affects the glomerular filtration barrier and leads to proteinuria. Podocyte-specific proteins like the transmembrane protein nephrin form the slit diaphragm that is important for proper function of the glomerular filtration barrier. Sodium-glucose co-transporter 2 (SGLT2) specific proteins are involved in glucose reabsorption in the kidney and maintain the normal glucose level in the blood. Recent studies showed remarkable success of SGLT2-inhibition in patients with diabetic nephropathy. Therefore we wanted to study if hyperglycemia induced reduction of nephrin expression is affected bySGLT-2 inhibition. Therefore we induced hyperglycemia in zebrafish larvae by knockdown of Pancreatic duodenal homeobox 1 (Pdx1) transcription factor and treated zebrafish larvae with Empagliflozin. In parallel we treated Bl/6 mice with streptozotozin and treated them with Empagliflozin. We then analyzed nephrin expression in both model systems.

Method

Zebrafish is an ideal model to study glomerular diseases, because the zebrafish larvae develops a pronephros with high homology to the human glomerulus. In order to inhibit SLGT-2 after Pdx1-knockdown, we treated both control and diabetic zebrafish larvae with 10µM Empagliflozin from 1dpf to 5dpf. We used a zebrafish line that expresses a fluorescent Vitamin D binding plasma protein Tg(l-fabp:DBP:eGFP) to measure proteinuria by measuring the GFP signal in both retinal and glomerular vessels of 120 hpf larvae. Immunohistochemistry against nephrin was performed using a specific zebrafish antibody.

Results

Conclusion

Despite the promising effects of SLGT-2 inhibitor treatment in patients with diabetic nephropathy the early effects on nephrin expression are not addressed and remain an unchanged problem by this novel treatment option.

HIF-1α promotes cyst progression in a mouse model of autosomal dominant polycystic kidney disease

Autosomal dominant polycystic kidney disease (ADPKD) is mainly caused by mutations of the PKD1 gene and characterized by growth of bilateral renal cysts. Cyst growth is accompanied by regional hypoxia and induction of hypoxia-inducible factor (HIF)-1α in cyst-lining epithelial cells. To determine the relevance of HIF-1α for cyst growth in vivo we used an inducible kidney epithelium-specific knockout mouse to delete Pkd1 at postnatal day 20 or 35 to induce polycystic kidney disease of different severity and analyzed the effects of Hif-1α co-deletion and HIF-1α stabilization using a prolyl-hydroxylase inhibitor. HIF-1α expression was enhanced in kidneys with progressive cyst growth induced by early Pkd1 deletion, but unchanged in the milder phenotype induced by later Pkd1 deletion. Hif-1α co-deletion significantly attenuated cyst growth in the severe, but not in the mild, phenotype. Application of a prolyl-hydroxylase inhibitor resulted in severe aggravation of the mild phenotype with rapid loss of renal function. HIF-1α expression was associated with induction of genes that mediate calcium-activated chloride secretion. Thus, HIF-1α does not seem to play a role in early cyst formation, but accelerates cyst growth during progressive polycystic kidney disease. This novel mechanism of cyst growth may qualify as a therapeutic target.

Mild Salt-Sensitive Hypertension in Genetically Determined Low Nephron Number is Associated with Chloride but Not Sodium Retention

BACKGROUND/AIMS

One potential pathomechanism how low nephron number leads to hypertension in later life is altered salt handling. We therefore evaluated changes in electrolyte and water content in wildtype (wt) and GDNF+/- mice with a 30% reduction of nephron number.

METHODS

32 GDNF+/- and 36 wt mice were fed with low salt (LSD, 0.03%, normal drinking water) or high salt (HSD, 4%, 0.9% drinking water) diet for 4 weeks. Blood pressure was continuously measured by telemetry in a subgroup. At the end of the experiment and after standardized ashing processes electrolyte- and water contents of the skin and the total body were determined.

RESULTS

We found higher blood pressure in high salt treated GDNF+/-compared to wt mice. Of interest, we could not confirm an increase in total-body sodium as predicted by prevailing explanations, but found increased total body and skin chloride that interestingly correlated with relative kidney weight.

CONCLUSION

We hereby firstly report significant total body and skin chloride retention in salt sensitive hypertension of GDNF+/-mice with genetically determined lower nephron number. Thus, in contrast to the prevailing opinion our data argue for the involvement of non-volume related mechanisms.

Hypoxia inhibits nephrogenesis through paracrine Vegfa despite the ability to enhance tubulogenesis

Reduced nephron number predisposes to hypertension and kidney disease. Interaction of the branching ureteric bud and surrounding mesenchymal cells determines nephron number. Since oxygen supply may be critical for intrauterine development, we tested whether hypoxia and hypoxia-inducible factor-1α (HIF-1α) influence nephrogenesis. We found that HIF-1α is required for branching of MDCK cells. In addition, culture of metanephric mouse kidneys with ureteric bud cell-specific stabilization or knockout of HIF-1α revealed a positive impact of HIF-1α on nephrogenesis. In contrast, widespread stabilization of HIF-1α in metanephric kidneys through hypoxia or HIF stabilizers impaired nephrogenesis, and pharmacological HIF inhibition enhanced nephrogenesis. Several lines of evidence suggest an inhibitory effect through the hypoxia response of mesenchymal cells. HIF-1α was expressed in mesenchymal cells during nephrogenesis. Expression of the anti-branching factors Bmp4 and Vegfa, secreted by mesenchymal cells, was increased upon HIF stabilization. The conditioned medium from hypoxic metanephric kidneys inhibited MDCK branching, which was partially rescued by Vegfa antibodies. Thus, the effect of HIF-1α on nephrogenesis appears context dependent. While HIF-1α in the ureteric bud is of importance for proper branching morphogenesis, the net effect of hypoxia-induced HIF activation in the embryonic kidney appears to be mesenchymal cell-dependent inhibition of ureter branching.

Hypoxia-inducible factor-1α causes renal cyst expansion through calcium-activated chloride secretion

Polycystic kidney diseases are characterized by numerous bilateral renal cysts that continuously enlarge and, through compression of intact nephrons, lead to a decline in kidney function over time. We previously showed that cyst enlargement is accompanied by regional hypoxia, which results in the stabilization of hypoxia-inducible transcription factor-1α (HIF-1α) in the cyst epithelium. Here we demonstrate a correlation between cyst size and the expression of the HIF-1α-target gene, glucose transporter 1, and report that HIF-1α promotes renal cyst growth in two in vitro cyst models-principal-like MDCK cells (plMDCKs) within a collagen matrix and cultured embryonic mouse kidneys stimulated with forskolin. In both models, augmenting HIF-1α levels with the prolyl hydroxylase inhibitor 2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetate enhanced cyst growth. In addition, inhibition of HIF-1α degradation through tubule-specific knockdown of the von Hippel-Lindau tumor suppressor increased cyst size in the embryonic kidney cyst model. In contrast, inhibition of HIF-1α by chetomin and knockdown of HIF-1α both decreased cyst growth in these models. Consistent with previous reports, plMDCK cyst enlargement was driven largely by transepithelial chloride secretion, which consists, in part, of a calcium-activated chloride conductance. plMDCKs deficient for HIF-1α almost completely lacked calcium-activated chloride secretion. We conclude that regional hypoxia in renal cysts contributes to cyst growth, primarily due to HIF-1α-dependent calcium-activated chloride secretion. These findings identify the HIF system as a novel target for inhibition of cyst growth.

Renal protection by low dose irbesartan in diabetic nephropathy is paralleled by a reduction of inflammation, not of endoplasmic reticulum stress

Diabetes can disrupt endoplasmic reticulum (ER) homeostasis which leads to ER stress. ER stress-induced renal apoptosis seems to be involved in the development of diabetic nephropathy. The present study was designed to investigate the contribution of reduced ER stress to the beneficial effects of an angiotensin receptor blocker. Insulin-dependent diabetes mellitus was induced by streptozotocin injections to hypertensive mRen2-transgenic rats. After 2weeks animals were treated with 0.7mg/kg/day irbesartan. Blood glucose, blood pressure and protein excretion were assessed. Expression of ER stress markers was measured by real-time PCR. Immunohistochemistry was performed to detect markers of ER stress, renal damage and infiltrating cells. Glomerulosclerosis and apoptosis were evaluated. Diabetic mRen2-transgenic rats developed renal injury with proteinuria, tubulointerstitial cell proliferation as well as glomerulosclerosis and podocyte injury. Moreover, an increase in inflammation, podocyte ER stress and apoptosis was detected. Irbesartan somewhat lowered blood pressure and reduced proteinuria, tubulointerstitial cell proliferation and glomerulosclerosis. Podocyte damage was ameliorated but markers of ER stress (calnexin, grp78) and apoptosis were not reduced by irbesartan. On the other hand, inflammatory cell infiltration in the tubulointerstitium and the glomerulus was significantly attenuated. We conclude that irbesartan reduced renal damage even in a very low dose. The beneficial effects of low dose irbesartan were paralleled by a reduction of blood pressure and inflammation but not by a reduction of ER stress and apoptosis. Thus, sustained endoplasmic reticulum stress in the kidney does not necessarily lead to increased inflammation and tubulointerstitial or glomerular injury.

Hypoxia regulates the sperm associated antigen 4 (SPAG4) via HIF, which is expressed in renal clear cell carcinoma and promotes migration and invasion in vitro

Hypoxia leads to the upregulation of a variety of genes mediated largely via the hypoxia inducible transcription factor (HIF). Prominent HIF-regulated target genes such as the vascular endothelial growth factor (VEGF), the glucose transporter 1 (Glut-1), or erythropoietin (EPO) help to assure survival of cells and organisms in a low oxygenated environment. Here, we are the first to report the hypoxic regulation of the sperm associated antigen 4 (SPAG4). SPAG4 is a member of the cancer testis (CT) gene family and to date little is known about its physiological function or its involvement in tumor biology. A number of CT family candidate genes are therefore currently being investigated as potential cancer markers, due to their predominant testicular expression pattern. We analyzed RNA and protein expression by RNAse protection assay, immunofluorescent as well as immunohistological stainings. To evaluate the influence of SPAG4 on migration and invasion capabilities, siRNA knockdown as well as transient overexpression was performed prior to scratch or invasion assay analysis. The hypoxic regulation of SPAG4 is clearly mediated in a HIF-1 and VHL dependent manner. We furthermore show upregulation of SPAG4 expression in human renal clear cell carcinoma (RCC) and co-localization within the nucleolus in physiological human testis tissue. SPAG4 knockdown reduces the invasion capability of RCC cells in vitro and overexpression leads to enhancement of tumor cell migration. Together, SPAG4 could possibly play a role in the invasion capability and growth of renal tumors and could represent an interesting target for clinical intervention.

Tubulointerstitial de novo expression of the α8 integrin chain in a rodent model of renal fibrosis--a potential target for anti-fibrotic therapy?

In the normal kidney, the α8 integrin chain is expressed only on mesangial cells and vascular smooth muscle cells. α8 integrin ligates several matrix molecules including fibronectin, osteopontin and fibrillin-1. Recently, we detected de novo expression of α8 integrin on epithelial cells in renal cysts. We hypothesized that the α8 integrin chain is induced in tubular epithelia undergoing dedifferentiation and contributes to the fibrotic response in the tubulointerstitium (TI) after unilateral ureteral obstruction (UUO). After induction of UUO in rats by ligation of the right ureter, increased expression of the α8 integrin chain and its ligands was observed. In the TI, α8 integrin was localized to cytokeratin-positive epithelial cells and to interstitial fibroblasts; and colocalized with its ligands. In mice underexpressing α8 integrin UUO led to collagen deposition and fibroblast activation comparable to wild types. Mice lacking α8 integrin showed even more TI damage, fibroblast activation and collagen deposition after UUO compared to wild type mice. We conclude that the expression of the α8 integrin chain and its ligands is strongly induced in the TI after UUO, but underexpression of α8 integrin does not attenuate TI fibrosis. Mice lacking the α8 integrin chain are even more susceptible to TI damage than wild type mice. Thus, interactions of α8 integrin with its ligands do not seem to contribute to the development or progression of TI fibrosis in UUO. Targeting α8 integrin might not be a useful approach for anti-fibrotic therapy.

Hypoxia-inducible transcription factors stabilization in the thick ascending limb protects against ischemic acute kidney injury

Hypoxia-inducible transcription factors (HIF) protect cells against oxygen deprivation, and HIF stabilization before ischemia mitigates tissue injury. Because ischemic acute kidney injury (AKI) often involves the thick ascending limb (TAL), modulation of HIF in this segment may be protective. Here, we generated mice with targeted TAL deletion of the von Hippel-Lindau protein (Vhl), which mediates HIF degradation under normoxia, using Tamm-Horsfall protein (Thp)-driven Cre expression. These mice showed strong expression of HIF-1α in TALs but no changes in kidney morphology or function under control conditions. Deficiency of Vhl in the TAL markedly attenuated proximal tubular injury and preserved TAL function following ischemia-reperfusion, which may be partially a result of enhanced expression of glycolytic enzymes and lactate metabolism. These results highlight the importance of the thick ascending limb in the pathogenesis of AKI and suggest that pharmacologically targeting the HIF system may have potential to prevent and mitigate AKI.

The Raf kinase inhibitor PLX5568 slows cyst proliferation in rat polycystic kidney disease but promotes renal and hepatic fibrosis

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a common cause of renal failure. Aberrant epithelial cell proliferation is a major cause of progressive cyst enlargement in ADPKD. Since activation of the Ras/Raf signaling system has been detected in cyst-lining epithelia, inhibition of Raf kinase has been proposed as an approach to retard the progression of ADPKD. Methods and results. PLX5568, a novel selective small molecule inhibitor of Raf kinases, attenuated proliferation of human ADPKD cyst epithelial cells. It reduced in vitro cyst growth of Madin-Darby Canine Kidney cells and of human ADPKD cells within a collagen gel. In male cy/+ rats with polycystic kidneys, PLX5568 inhibited renal cyst growth along with a significant reduction in the number of proliferating cell nuclear antigen- and phosphorylated extracellular signal-regulated kinase-positive cyst-lining epithelial cells. Furthermore, treated animals showed increased capacity to concentrate urine. However, PLX5568 did not lead to a consistent improvement of renal function. Moreover, although relative cyst volume was decreased, total kidney-to-body weight ratio was not significantly reduced by PLX5568. Further analyses revealed a 2-fold increase of renal and hepatic fibrosis in animals treated with PLX5568.

CONCLUSIONS

PLX5568 attenuated cyst enlargement in vitro and in a rat model of ADPKD without improving kidney function, presumably due to increased renal fibrosis. These data suggest that effective therapies for the treatment of ADPKD will need to target fibrosis as well as the growth of cysts.

The GTPase RAB20 is a HIF target with mitochondrial localization mediating apoptosis in hypoxia

Hypoxia is a common pathogenic stress, which requires adaptive activation of the Hypoxia-inducible transcription factor (HIF). In concert transcriptional HIF targets enhance oxygen availability and simultaneously reduce oxygen demand, enabling survival in a hypoxic microenvironment. Here, we describe the characterization of a new HIF-1 target gene, Rab20, which is a member of the Rab family of small GTP-binding proteins, regulating intracellular trafficking and vesicle formation. Rab20 is directly regulated by HIF-1, resulting in rapid upregulation of Rab20 mRNA as well as protein under hypoxia. Furthermore, exogenous as well as endogenous Rab20 protein colocalizes with mitochondria. Knockdown studies reveal that Rab20 is involved in hypoxia induced apoptosis. Since mitochondria play a key role in the control of cell death, we suggest that regulating mitochondrial homeostasis in hypoxia is a key function of Rab20. Furthermore, our study implicates that cellular transport pathways play a role in oxygen homeostasis. Hypoxia-induced Rab20 may influence tissue homeostasis and repair during and after hypoxic stress.

Evidence for a lack of a direct transcriptional suppression of the iron regulatory peptide hepcidin by hypoxia-inducible factors

Background

Hepcidin is a major regulator of iron metabolism and plays a key role in anemia of chronic disease, reducing intestinal iron uptake and release from body iron stores. Hypoxia and chemical stabilizers of the hypoxia-inducible transcription factor (HIF) have been shown to suppress hepcidin expression. We therefore investigated the role of HIF in hepcidin regulation.

Methodology/Principal Findings

Hepcidin mRNA was down-regulated in hepatoma cells by chemical HIF stabilizers and iron chelators, respectively. In contrast, the response to hypoxia was variable. The decrease in hepcidin mRNA was not reversed by HIF-1α or HIF-2α knock-down or by depletion of the HIF and iron regulatory protein (IRP) target transferrin receptor 1 (TfR1). However, the response of hepcidin to hypoxia and chemical HIF inducers paralleled the regulation of transferrin receptor 2 (TfR2), one of the genes critical to hepcidin expression. Hepcidin expression was also markedly and rapidly decreased by serum deprivation, independent of transferrin-bound iron, and by the phosphatidylinositol 3 (PI3) kinase inhibitor LY294002, indicating that growth factors are required for hepcidin expression in vitro. Hepcidin promoter constructs mirrored the response of mRNA levels to interleukin-6 and bone morphogenetic proteins, but not consistently to hypoxia or HIF stabilizers, and deletion of the putative HIF binding motifs did not alter the response to different hypoxic stimuli. In mice exposed to carbon monoxide, hypoxia or the chemical HIF inducer N-oxalylglycine, liver hepcidin 1 mRNA was elevated rather than decreased.

Conclusions/Significance

Taken together, these data indicate that hepcidin is neither a direct target of HIF, nor indirectly regulated by HIF through induction of TfR1 expression. Hepcidin mRNA expression in vitro is highly sensitive to the presence of serum factors and PI3 kinase inhibition and parallels TfR2 expression.

HIF-prolyl hydroxylases in the rat kidney: physiologic expression patterns and regulation in acute kidney injury

Hypoxia-inducible transcription factors (HIFs) play important roles in the response of the kidney to systemic and regional hypoxia. Degradation of HIFs is mediated by three oxygen-dependent HIF-prolyl hydroxylases (PHDs), which have partially overlapping characteristics. Although PHD inhibitors, which can induce HIFs in the presence of oxygen, are already in clinical development, little is known about the expression and regulation of these enzymes in the kidney. Therefore, we investigated the expression levels of the three PHDs in both isolated tubular cells and rat kidneys. All three PHDs were present in the kidney and were expressed predominantly in three different cell populations: (a) in distal convoluted tubules and collecting ducts (PHD1,2,3), (b) in glomerular podocytes (PHD1,3), and (c) in interstitial fibroblasts (PHD1,3). Higher levels of PHDs were found in tubular segments of the inner medulla where oxygen tensions are known to be physiologically low. PHD expression levels were unchanged in HIF-positive tubular and interstitial cells after induction by systemic hypoxia. In rat models of acute renal injury, changes in PHD expression levels were variable; while cisplatin and ischemia/reperfusion led to significant decreases in PHD2 and 3 expression levels, no changes were seen in a model of contrast media-induced nephropathy. These results implicate the non-uniform expression of HIF-regulating enzymes that modify the hypoxic response in the kidney under both regional and temporal conditions.

Hypertension induces somatic cellular senescence in rats and humans by induction of cell cycle inhibitor p16INK4a

There is increasing evidence for a role of somatic cellular senescence in physiological aging but also in injury and disease. Cell cycle inhibitor p16(INK4a) is the key mediator for stress and aberrant signaling induced senescence. Here we report that elevated blood pressure markedly induced p16(INK4a) expression in rat kidneys and hearts, as well as in human kidneys. In kidneys from deoxycorticosterone acetate-salt-treated rats, p16(INK4a) induction was found in tubular, glomerular, interstitial, and vascular cells and correlated with the typical histopathologic features of hypertensive target organ damage. p16(INK4a) expression also correlated with phospho-p38, a positive upstream regulator of p16(INK4a) expression. In left ventricles, increased p16(INK4a) expression was found in myocardium and cardiac arteries. Antihypertensive medication consistent of hydrochlorothiazide, hydralazine, and reserpine ameliorated the histopathologic changes and attenuated p16(INK4a) expression in kidneys of deoxycorticosterone acetate-salt-treated rats. Nonantihypertensive administration of spironolactone also reduced kidney damage and p16(INK4a) expression. p16(INK4a) induction was further observed in kidneys from hypertensive transgenic rats heterozygous for the mouse Ren-2 gene and was prevented by the angiotensin II type 1 receptor blocker losartan. In human kidney biopsies showing hypertensive nephrosclerosis, increased p16(INK4a) expression was found compared with age-matched normotensive control subjects. Thus, hypertension induces cellular senescence via p16(INK4a), possibly through p38, thereby contributing to hypertensive target organ damage. This detrimental effect can be overcome by different therapeutic drug strategies.

HIF activation protects from acute kidney injury

The contribution of hypoxia to cisplatin-induced renal tubular injury is controversial. Because the hypoxia-inducible factor (HIF) pathway is a master regulator of adaptation to hypoxia, we measured the effects of cisplatin on HIF accumulation in vitro and in vivo, and tested whether hypoxic preconditioning is protective against cisplatin-induced injury. We found that cisplatin did not stabilize HIF-1alpha protein in vitro or in vivo under normoxic conditions. However, hypoxic preconditioning of cisplatin-treated proximal tubular cells in culture reduced apoptosis in an HIF-1alpha-dependent fashion and increased cell proliferation as measured by BrdU incorporation. In vivo, rats preconditioned with carbon monoxide before cisplatin administration had significantly better renal function than rats kept in normoxic conditions throughout. Moreover, the histomorphological extent of renal damage and tubular apoptosis was reduced by the preconditional treatment. Therefore, development of pharmacologic agents to induce renal HIF might provide a new approach to ameliorate cisplatin-induced nephrotoxicity.

The tumor gene survivin is highly expressed in adult renal tubular cells: implications for a pathophysiological role in the kidney

The inhibitor of apoptosis protein survivin is of critical importance for regulation of cellular division and survival. Published data point to a restricted function of survivin in embryonic development and cancer; thus survivin has been broadly proposed as an ideal molecular target for specific anti-cancer therapy. In contrast to this paradigm, we report here broad expression of survivin in adult differentiated tissues, as demonstrated at the mRNA and protein levels. Focusing on the kidney, survivin is strongly expressed in proximal tubuli, particularly at the apical membrane, which can be verified in rat, mouse, and human kidneys. In the latter, survivin expression seems to be even stronger in proximal tubuli than in adjacent cancerous tissue. Primary and immortalized human renal tubular cells also showed high levels of survivin protein expression, and RNA interference resulted in a partial G(2)/M arrest of the cell cycle and increased rate of apoptosis. In conclusion, survivin may be of importance for renal pathophysiology and pathology. The predominant apical expression of survivin may indicate a further, yet unknown, function. Interventional strategies to inhibit survivin's function in malignancy need to be carefully (re)evaluated for renal side effects, as well as for other possible organ dysfunctions.

(Pro)renin receptor peptide inhibitor "handle-region" peptide does not affect hypertensive nephrosclerosis in Goldblatt rats

The (pro)renin receptor [(P)RR], a new component the renin-angiotensin system, was cloned recently. The (P)RR promotes direct mitogen-activated protein kinase signaling and nonproteolytic prorenin activation. We investigated the role of a (P)RR blocker, a peptide consisting of 10 amino acids from the prorenin prosegment called the "handle-region" peptide (HRP), on target organ damage in renovascular hypertensive 2-kidney, 1-clip (2K1C) rats. Vehicle-treated 2K1C rats were compared with HRP-treated 2K1C rats (3.5 mug/kg per day) and sham-operated controls. Vehicle-treated 2K1C rats developed hypertension (186+/-17 mm Hg), cardiac hypertrophy (3.16+/-0.16 mg/g), renal inflammation, fibrosis, vascular, and tubular damage. Chronic HRP treatment did not affect blood pressure (194+/-15 mm Hg), cardiac hypertrophy (2.97+/-0.11 mg/g), or renal damage. Furthermore, we investigated the renal renin and (P)RR expression. The clipped kidney of 2K1C and HRP-treated 2K1C rats showed a higher renin expression and juxtaglomerular index compared with sham-operated kidneys. The unclipped kidney showed suppressed renin expression. In contrast, (P)RR mRNA expression was not altered in any group. Plasma renin activity and aldosterone were increased in 2K1C rats compared with sham controls. HRP-treated 2K1C rats tended to lower plasma renin activity but showed similar aldosterone levels as vehicle-treated 2K1C rats. Our results indicate that blockade of the (P)RR with HRP does not improve target organ damage in renovascular hypertensive rats.

Hypoxia, via stabilization of the hypoxia-inducible factor HIF-1alpha, is a direct and sufficient stimulus for brain-type natriuretic peptide induction

BNP (brain-type natriuretic peptide) is a cardiac hormone with systemic haemodynamic effects as well as local cytoprotective and antiproliferative properties. It is induced under a variety of pathophysiological conditions, including decompensated heart failure and myocardial infarction. Since regional hypoxia is a potential common denominator of increased wall stretch and myocardial hypoperfusion, we investigated the direct effects of hypoxia on BNP expression, and the role of the HIF (hypoxia-inducible transcription factor) in BNP regulation. Using an RNase protection assay we found a strong hypoxic induction of BNP mRNA expression in different cell lines and in cultured adult rat cardiomyocytes. Systemic hypoxia and exposure to 0.1% CO induced BNP expression in the rodent myocardium in vivo, although this was at a lower amplitude. BNP promoter-driven luciferase expression increased 10-fold after hypoxic stimulation in transient transfections. Inactivation of four putative HREs (hypoxia-response elements) in the promoter by site-directed mutagenesis revealed that the HRE at -466 nt was responsible for hypoxic promoter activation. A functional CACAG motif was identified upstream of this HRE. The HIF-1 complex bound specifically and inducibly only to the HRE at -466 nt, as shown by EMSA (electrophoretic mobility-shift assay) and ChIP (chromatin immunoprecipitation). siRNA (small interfering RNA)-mediated knockdown of HIF-1alpha, but not HIF-2alpha, interfered with hypoxic BNP mRNA induction and BNP promoter activation, confirming that BNP is a specific HIF-1alpha target gene. In conclusion, BNP appears to be part of the protective program steered by HIF-1 in response to oxygen deprivation. Induction of BNP may therefore contribute to the potential benefits of pharmacological HIF inducers in the treatment of ischaemic heart disease and heart failure.

Renal phenotype in heterozygous Lmx1b knockout mice (Lmx1b +/−) after unilateral nephrectomy

The nail-patella syndrome (NPS) is a rare autosomal-dominant disorder which is caused by loss-of-function mutations in the transcription factor LMX1B. NPS is characterized by dysplastic nails, absent or hypoplastic patellae, minor skeletal abnormalities and nephropathy (in 20-40% of the cases), which is the most severe aspect of the disorder. The current data suggest that genetic modifiers in the outbred human genetic background are responsible for this variable phenotype. Preliminary work on the function of Lmx1b in the kidney has been performed using Lmx1b knockout mice (Lmx1b (-/-)). Although Lmx1b (-/-) mice die within 24 h after birth, they exhibit the characteristic NPS features including the renal abnormalities. But in contrast to the situation in human, no phenotype could so far be detected in heterozygous Lmx1b (+/-) mice. This indicates that our understanding of the pathomechanism underlying the nephropathy is still very limited. In an attempt to further evaluate these mechanisms, we tried to induce a renal phenotype in Lmx1b (+/-) mice, and thus model the human (NPS) situation. We applied unilateral nephrectomy as a model to induce nephron loss and detected a significant (p = 0.02) reduction in compensatory renal growth in heterozygous knockout animals (Lmx1b (+/-)) compared to Lmx1b (+/+) animals, which was correlated with a significantly lower increase in glomerular volume (V(G)) (p = 0.0034) and an increase in glomerulosclerosis (p = 0.085). Thus, Lmx1b deficiency in heterozygous Lmx1b (Lmx1b (+/-)) knockout mice profoundly affects the compensatory response to nephron loss. Moreover, this is the first report of a phenotype in heterozygous Lmx1b (Lmx1b ( +/-)) knockout animals.

Effect of the angiotensinogen genotype on experimental hypertension in mice

Polymorphisms of the angiotensinogen (Agt) gene may affect blood pressure. We used a mouse model to test for the role of the Agt genotype in low-renin or high-renin forms of hypertension. Mice bearing one, two, three, or four copies of the Agt gene underwent renal artery clipping to induce high-renin two-kidney, one-clip renovascular hypertension (2K1C), or uninephrectomy, salt loading, and application of deoxycorticosterone-acetate (DOCA) pellets to induce low-renin mineralocorticoid hypertension. Appropriate control animals were also studied. Blood pressure was measured by tail cuff as well as by direct intra-arterial recordings. There was a small effect of the Agt genotype on baseline blood pressure before induction of hypertension. The extent of 2K1C hypertension was not affected by the genotype. In contrast, there was a marked gene-dose effect on DOCA-hypertension (21.2 mmHg over all genotypes). Treatment of DOCA mice with the angiotensin II type 1 receptor antagonist abolished the genotype effect on blood pressure and left ventricular hypertrophy. There was a trend towards less suppression of endogenous aldosterone by DOCA treatment with increasing number of Agt gene copies. We conclude that the Agt genotype exerts a marked effect on blood pressure in a low-renin form of hypertension but no effect in the face of stimulated renin, at least in mice.

Renal injury in streptozotocin-diabetic Ren2-transgenic rats is mainly dependent on hypertension, not on diabetes

Induction of streptozotocin (STZ) diabetes in hypertensive rats transgenic for the mouse ren-2 gene (TGR) has been described as a model of progressive diabetic nephropathy. We investigated the long-term course of STZ diabetes in TGR and appropriate Sprague-Dawley control rats (SD) and tested the role of angiotensin-dependent hypertension by treating rats with the angiotensin II type 1 receptor blocker losartan (1 mg·kg−1·day−1) via osmotic minipumps. Five weeks after STZ injection, diabetes developed in TGR and SD. Urinary albumin excretion was increased by diabetes and, to a much higher degree, by hypertension. The effects of hypertension and diabetes were not additive, and only the effects of hypertension were ameliorated by losartan. A similar pattern was observed for cell proliferation and macrophage infiltration in the kidney. In contrast, the effects of hypertension and diabetes on glomerular collagen IV accumulation were additive 5 wk after STZ injection. In a long-term study for 20 wk after STZ, survival was better in STZ-treated TGR than in normoglycemic TGR, whereas all SD survived. Impaired creatinine clearance and increased macrophage infiltration as well as glomerular and interstitial matrix deposition were prominent in TGR compared with SD, regardless of the presence or absence of diabetes. In conclusion, STZ diabetes in TGR may be useful to study glomerular and interstitial matrix deposition early in the course of diabetes. However, the long-term course of this animal model resembles severe hypertensive nephrosclerosis, rather than progressive diabetic nephropathy.

Role of fibrillin-1 in hypertensive and diabetic glomerular disease

The microfibrillar protein fibrillin-1 is a component of the mesangial matrix. Defects in fibrillin-1 predisposes individuals to vascular damage in Marfan syndrome, but the role of fibrillin-1 in kidney disease is unknown. We hypothesized that fibrillin-1 is involved in hypertensive or diabetic glomerular disease. DOCA-salt hypertension or streptozotocin (STZ) diabetes led to a significant increase in glomerular fibrillin-1 deposition. To test the functional role of fibrillin-1, DOCA hypertension and STZ diabetes were induced in mice homozygous for a mutation leading to a fivefold lower expression of fibrillin-1 (mgR/mgR). Untreated male mgR/mgR mice usually die from aortic dissection during the first 4 mo of life. All DOCA-treated mgR/mgR mice died within 2 wk after onset of DOCA treatment. DOCA-treated heterozygous (mgR/+) and their wild-type littermates displayed similar blood pressure levels, but albuminuria was significantly lower in mgR/+ than in wild-type mice after DOCA treatment. Similarly, STZ diabetic mgR/mgR and mgR/+ developed lower albuminuria than wild-type mice despite higher blood glucose levels in mgR/mgR and mgR/+ compared with wild-type mice. Blood pressure, blood glucose, and albuminuria did not differ among untreated mgR/mgR, mgR/+, and wild-type mice, respectively. In diabetic mgR/+ and mgR/mgR, but not in wild-type mice, an induction of glomerular decorin expression was observed. Thus underexpression of fibrillin-1 predisposes individuals to lethal aortic dissection in the presence of hypertension. On the other hand, albuminuria as a parameter of microvascular damage in hypertension and diabetes was ameliorated in fibrillin-1-underexpressing mice, possibly due to a compensatory upregulation of decorin. We conclude that fibrillin-1 may contribute to glomerular damage in hypertensive and diabetic kidney disease.

Angiotensin II formation in the kidney and nephrosclerosis in Ren-2 hypertensive rats

BACKGROUND

Ren-2 transgenic hypertensive rats develop malignant hypertensive nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin. We tested the hypothesis that local angiotensin II formation occurs at sites of renal vascular and interstitial injury in this model.

METHODS

Heterozygous Ren-2 transgenic rats were compared with normotensive Sprague-Dawley-Hannover control rats and Ren-2 transgenic rats treated with a very low dose of an angiotensin II type 1 (AT1) receptor antagonist, 1 mg/kg/day losartan, for 4 weeks. Blood pressure measurements, quantifications of urinary albumin, plasma and tissue angiotensin II as well as immunohistochemical analyses were performed.

RESULTS

Systolic blood pressure was not affected by losartan during the study but intra-arterial recordings revealed a decrease of blood pressure. Losartan reduced albumin excretion, cell proliferation, macrophage influx, collagen I and collagen IV deposition. Plasma angiotensin II was decreased, while kidney tissue angiotensin II content was increased in Ren-2 transgenic rats compared with control rats. In Ren-2 transgenic rats, juxtaglomerular renin and angiotensin II staining were reduced, but there was a marked angiotensin II staining at foci of tubulo-interstitial fibrosis and at proliferative malignant vascular lesions.

CONCLUSION

We conclude that local angiotensin II formation is increased in proliferative or fibrotic kidney lesions in the Ren-2 transgenic rat. Local angiotensin II formation may help to explain why the AT1 receptor antagonist prevents or ameliorates this transgenic model of malignant nephrosclerosis despite low to normal plasma angiotensin II and suppressed renal renin.

Adrenomedullin reduces mesangial cell number and glomerular inflammation in experimental mesangioproliferative glomerulonephritis

BACKGROUND

Adrenomedullin (ADM) is a vasodilator peptide that is abundantly expressed in the kidney. ADM has antiproliferative effects on glomerular mesangial cells (MC) in vitro. Whether or not treatment with ADM can reduce MC proliferation in vivo [i.e., in mesangioproliferative glomerulonephritis (GN)] is unknown. We tested the hypothesis that ADM substitution reduces MC proliferation in GN.

METHODS

GN in rats was induced by injection of an anti-Thy-1.1 antibody. Rats received osmotic minipumps, which continuously delivered rat ADM (500 ng/hour, N = 11), or vehicle (N = 13) from day 3 to day 6 after GN induction. Rats were sacrificed 6 days after induction of GN. On kidney sections, cells staining positive for proliferating cell nuclear antigen, mesangial cells, monocytes, and apoptotic cells were counted. Parameters of inflammation and fibrosis were measured in renal cortex and sieved glomeruli by real-time polymerase chain reaction (PCR).

RESULTS

Systolic blood pressure, diuresis, albuminuria, creatinine clearance, microaneurysm formation, and mesangial matrix expansion were not influenced by ADM infusion. However, ADM treatment significantly reduced the number of MC, showed a tendency to reduce total glomerular cell proliferation, and significantly increased apoptosis. ADM-treated GN animals showed significantly less glomerular monocyte infiltration. ADM treatment normalized transforming growth factor (TGF)-beta1 mRNA expression and reduced monocyte chemoattractant protein-1 (MCP-1), osteopontin, plasminogen activator inhibitor-1 (PAI-1), collagen I, and collagen III mRNA expression significantly.

CONCLUSION

Exogenous ADM infusion reduces MC number and glomerular monocyte infiltration in the state of mesangial proliferation during acute experimental mesangioproliferative GN. These findings indicate that ADM can influence the course of mesangioproliferative GN.

Transplantation-induced functional/morphological changes in rat aorta allografts differ from those in arteries of rat kidney allografts

The functional/morphological changes observed in rat aorta allografts were compared with those seen in the arteries of rat kidney allografts. Untreated allografts (F344-to-LEW) were collected at various times post-transplantation (Tx). Vascular smooth muscle cell (SMC) constriction to phenylephrine (Phe) and endothelial cell (EC)-dependent relaxation to acetylcholine (Ach) were assessed. Neointima formation in graft vessels was assessed by histology. In aorta allografts, the effects of Phe and Ach were irreversibly abolished within 3-2 weeks post-Tx. Neointima formation was consistently detected between 4 and 8 weeks post-Tx. In kidney allografts, sign of vasculopathy was seen in 10, 30 and 40% of resistance arteries at 8, 16 and 33 weeks post-Tx, respectively. In the main renal artery, substantial neointima formation was not apparent before 33 weeks post-Tx, the vasoconstrictor effect of Phe was fully maintained until then, and Ach-induced vasorelaxation was irreversibly reduced by approximately 70% from week 2 post-Tx onwards. These results indicate that the post-Tx functional/morphological changes seen in aorta allografts do not reflect those seen in arteries of kidney allografts. Hence, renal arteries from rat kidney allografts can be considered as a more relevant model to study the cascade of events leading to Tx-induced CGA in solid organ allografts.

Strain differences in the development of hypertension and glomerular lesions induced by deoxycorticosterone acetate salt in mice

BACKGROUND

The genetic background may exert important modifying effects on the course and severity of experimental kidney diseases in mice. We investigated its influence on the development of hypertension and renal injury following treatment with deoxycorticosterone acetate (DOCA) salt in several mouse strains.

METHODS

Four mouse strains were used for comparison: 129/Sv, C57BL/6 and F1 and F2 intercrosses of 129/Sv x C57BL/6. Male mice were uninephrectomized and DOCA hypertension was induced for 6 weeks. DOCA animals and controls received 1% NaCl for drinking. Renal damage was evaluated following measurements of blood pressure, urine albumin and renal matrix expansion.

RESULTS

DOCA-induced blood pressure increase, glomerulosclerosis, interstitial fibrosis and albuminuria were markedly higher in 129/Sv than in C57BL/6 mice. F1 and F2 intercrosses displayed intermediate blood pressure, glomerular and interstitial fibrosis comparable to C57BL/6 but albuminuria as high as 129/Sv mice.

CONCLUSIONS

129/Sv mice are more susceptible to the development of DOCA-induced high blood pressure and renal damage than C57BL/6 mice. Intercrosses of both strains show a complex and non-uniform segregation of the susceptibility to DOCA-salt hypertension and nephrosclerosis.

The alpha8 integrin chain affords mechanical stability to the glomerular capillary tuft in hypertensive glomerular disease

In the kidney, the alpha8 integrin chain is expressed in glomerular mesangial cells. The alpha8 integrin plays a role in early nephrogenesis but its functional role in the adult kidney is unknown. We tested the hypothesis that alpha8 integrin-mediated cell-matrix interactions are important to maintain the integrity of the glomerulus in arterial hypertension. Desoxycorticosterone (DOCA)-salt hypertension was induced in mice homozygous for a deletion of the alpha8 integrin chain and wild-type mice. Blood pressure, albumin excretion, total renal mass, and glomerular filtration in DOCA-treated alpha8-deficient mice were comparable to DOCA-treated wild types. DOCA-treated wild types showed increased glomerular immunostaining for alpha8 integrin compared to salt-loaded and untreated controls, whereas the glomeruli of alpha8-deficient mice always stained negative. Morphometric studies revealed similar degrees of glomerulosclerosis in DOCA-treated alpha8-deficient and DOCA-treated wild-type mice. However, DOCA-treated alpha8-deficient mice had a higher score of capillary widening (mesangiolysis) than DOCA-treated wild-type mice, which was confirmed in two additional wild-type strains. Moreover, in DOCA-treated alpha8-deficient mice, glomerular fibrin deposits were more frequent than in DOCA-treated wild types. The results show that lack of alpha8 is associated with increased susceptibility to glomerular capillary destruction in DOCA salt hypertension, whereas it does not seem to play a major role in the development of fibrosis or glomerulosclerosis. Our findings indicate that mesangial alpha8 integrin contributes to maintain the integrity of the glomerular capillary tuft during mechanical stress, eg, in hypertension.

Effects of vascular endothelial growth factor (VEGF)/vascular permeability factor (VPF) on haemodynamics and permselectivity of the isolated perfused rat kidney

BACKGROUND

Vascular endothelial growth factor (VEGF) or vascular permeability factor (VPF) is a selective mitogen for endothelial cells; it increases microvascular permeability and has been shown to relax isolated canine coronary arteries by an endothelium-dependent mechanism. In many tissues VEGF/VPF is expressed after an appropriate stimulus, mostly hypoxia. In the kidney VEGF/VPF is constitutively expressed in glomerular podocytes and epithelia of collecting duct. Glomerular and peritubular capillary endothelia also constitutively express specific VEGF receptors. The in vivo function of renal VEGF/VPF is unknown.

METHOD

In the present study the effects of human recombinant VEGF165 on renal haemodynamics and glomerular permselectivity was investigated in the isolated perfused kidney of the rat.

RESULTS

In kidneys preconstricted by noradrenaline (NA 1.5 x 10(-7) mol/l) VEGF/VPF (155 pmol/l) caused an almost complete return of renal perfusion flow rate to pre-NA values (before NA 113 +/- 4%, after NA 100%, 15 min with VEGF/VPF 111 +/- 4%). Shortly after VEGF/VPF administration VEGF/VPF-induced relaxation commenced, and became significant after 2 min (15 min with VEGF/VPF vs without VEGF/VPF 111 +/- 4% vs 103 +/- 2%; P<0.05). In the presence of the NO-synthase inhibitor N(W)-nitro-L-arginine (L-NNA; 5 x 10(-5) mol/l) VEGF/VPF caused only small, transient relaxations (before NNA 109 +/- 5%, after NNA 100%, 15 min with VEGF 95 +/- 2%). The cyclooxygenase inhibitor diclofenac failed to inhibit the relaxing activity of VEGF/VPF (before NA 119 +/- 4%, after NA + diclofenac 100%, 15 min with VEGF/VPF 123 +/- 5%). VEGF demonstrated no significant increase in renal protein excretion rate (after NA pretreatment (= 100%): 12.5 min with VEGF/VPF vs without VEGF/VPF: 119 +/- 10% vs 132 +/- 11%, n.s.) (after NNA pretreatment (= 100%) 12.5 min with VEGF/VPF vs without VEGF/VPF 94 +/- 5% vs 96 +/- 4%; n.s.) or clearance quotient of albumin. Glomerular filtration rate was not influenced by VEGF/VPF in kidneys pretreated with NA (before NA 105 +/- 5%, after NA 100%, 12.5 min with VEGF/VPF 94 +/- 2%) or with NNA (before NNA 107 +/- 6%, after NNA 100%, 12.5 min with VEGF/VPF 96 +/- 2%). Fractional glucose and fractional sodium excretion showed flow-dependent changes.

CONCLUSION

VEGF/VPF can contribute to the relaxing capacity of the renal vasculature. This relaxation is partly mediated by the NO/endothelium-derived relaxing factor (EDRF) pathway. In the isolated perfused rat kidney the glomerular permeability for albumin is not affected by VEGF/VPF.

Enhanced renal allograft rejection by inhibitors of nitric oxide synthase: a nonimmunologic influence on alloreactivity

Clinical and experimental studies indicate that nonimmunologic factors may modulate the alloreactivity of a renal transplant. Nitric oxide (NO) is an essential modulator of endothelial function. It was postulated that, in renal allografts, inhibition of constitutive NO synthase may lead to an aggravation of immunologic damage to endothelia and therefore may enhance dysfunction of the graft. Male Lewis (RT1l) rats received syngeneic or allogeneic Brown Norway (RT1n) renal grafts and were treated with cyclosporin A (CyA) or with CyA and an NO synthase blocker (NOS-B): N omega-nitro-L-arginine (L-NNA) or NG-monomethyl-L-arginine (L-NMMA). CyA was given at a dose of 3.5 mg/kg body weight for 14 days and the NOS-B at a dose of 66 mg/L drinking water for up to 28 days postoperatively. Animals (N = 6/group) were studied at 4 to 7, 14, and 28 days posttransplantation. Four to 5 days posttransplantation, renal blood flow and glomerular filtration rate of allogeneic grafts did not differ between animals treated only with CyA and those treated with CyA and NOS-B. Mean arterial pressure was significantly elevated by NOS-B (CyA+L-NNA: 115 +/- 13 versus CyA: 78 +/- 16 mm Hg). Combined NOS-B and CyA administration led to a pronounced increase in vascular and tubulointerstitial damage. The number of mononuclear cells in vessels, glomeruli, and tubulointerstitium increased significantly in allografts upon treatment with NOS-B. During NOS-B administration, adhesion molecules (intracellular adhesion molecule-1; leukocyte-function-associated molecules-1 alpha and-beta) were strongly expressed in endothelial and leukocytic cells of the allograft. A pronounced positivity for mRNA and protein of cytokines tumor necrosis factor-alpha and transforming growth factor-beta could be demonstrated in the inflammatory infiltrate. With L-NNA treatment, the total vascular injury index was 10-fold higher (14 days posttransplantation, CyA+L-NNA: 59.8 +/- 11.7 versus CyA: 6.0 +/- 1.8; p < 0.05). The tubulointerstitial damage score rose more than 2.5-fold after CyA and L-NNA therapy (28 days posttransplantation: CyA+L-NNA: 83 +/- 1 versus CyA:29 +/- 1). L-NNA was more potent than L-NMMA at the dosages used. Thus, pronounced vascular leukostasis, vasculitis, and T-cell and monocyte infiltration of the tubulointerstitium led to a severe damage of the allograft under therapy with CyA and NOS-B. Inhibition of NO synthesis may aggravate alloreactive immunemediated injury in kidney transplants acting primarily by a disturbance of endothelial function.

Importance of NO/EDRF for glomerular and tubular function: studies in the isolated perfused rat kidney

The effect of the addition of N omega-nitro-L-arginine (L-NNA, 10 and 100 microM) to isolated rat kidneys perfused with a complex medium containing 21 amino acids has been studied. A cyclooxygenase inhibitor was added throughout to block prostaglandin synthesis. L-NNA caused significant reductions in renal perfusion flow rate (PFR, 9.8 +/- 1.4 vs. 15.9 +/- 1.1 ml.min-1.g kidney wt-1, P less than 0.0001), glomerular filtration rate (GFR, 566 +/- 57 vs. 705 +/- 47 microliters.min-1.g kidney wt-1, P less than 0.05) and an increase in the relative filtration fraction (%FF, 7.0 +/- 0.6 vs. 5.2 +/- 0.4%, P less than 0.05) compared to control kidneys. L-NNA perfused kidneys had a lower absolute sodium (72 +/- 9 vs. 88 +/- 4 mumol.min-1.g kidney wt-1, P less than 0.05) and glucose reabsorption (3.5 +/- 0.5 vs. 5.4 +/- 0.4 mumol.min-1.g kidney wt-1, P less than 0.05), corresponding mainly to a lower sodium and glucose filtration. However, the relative reabsorption of sodium and glucose in the presence of L-NNA was attenuated, too (82.8 +/- 2.0 vs. 87.0 +/- 3.3% P less than 0.05 and 91.3 +/- 1.1 vs. 94.1 +/- 0.5%, P less than 0.05). Potassium handling and protein excretion were not changed significantly; fractional protein excretion increased slightly with the addition of L-arginine (47 +/- 5 vs. 55 +/- 7 ng.microliters-1, P less than 0.05). The differences between control and L-NNA treated kidneys (with the exception of differences in FRGluc) could be fully (L-NNA, 10 microM) or partially (L-NNA 100 microns) reversed by adding L-arginine (1 mM) to the perfusion medium. The observed results could be obtained in two different rat strains (Sprague-Dawley and Wistar). Only L-NNA and L-arginine caused the observed changes, while D-NNA and D-arginine were without effect. It is concluded that NO/EDRF is basally released from the isolated perfused rat kidney, and is of importance not only in the regulation of renal hemodynamics but also in the regulation of renal tubular function.

Effect of arginine depletion on glomerular and tubular kidney function: studies in isolated perfused rat kidneys

The effect of L-Arg depletion on glomerular hemodynamics and tubular function of isolated rat kidneys perfused with a medium containing 21 amino acids has been studied. A cyclooxygenase inhibitor was added throughout for blockade of prostaglandin synthesis. Arg depletion caused significant (approximately 30%) reductions in renal perfusion flow rate (PFR, 13.9 +/- 1.2 vs. 19.8 +/- 0.6 ml.min-1.g (kidney wt-1), glomerular filtration rate (GFR, 598 +/- 79 vs. 924 +/- 42 microliters.min-1.g kidney wt-1), and urine flow rate (139 +/- 38 vs. 192 +/- 13 microliters.min-1.g kidney wt-1) compared with control kidneys, which were perfused with a physiological concentration of Arg (200 microM). Filtration fraction (FF) increased with Arg depletion (5.1 +/- 0.4 vs. 4.4 +/- 0.4%). Arg-depleted kidneys had a lower absolute sodium (TNa, 75.7 +/- 8.8 vs. 107.9 +/- 6.0 mumol.min-1.g kidney wt-1) and glucose reabsorption (T glucose, 3.7 +/- 0.6 vs. 5.6 +/- 0.5 mumol.min-1.g kidney wt-1), corresponding to a lower sodium and glucose filtration. Potassium handling and reabsorption of free water were not changed. Oxygen consumption (QO2) was lower in Arg-depleted kidneys (4.6 +/- 0.3 vs. 5.5 +/- 0.5 mumol.min-1.g kidney wt-1). The effects of Arg depletion were completely reversed by the addition of Arg (1 mM) at 120 min and partly reversed by the addition of citrulline (1 mM). Ornithine depletion or addition had no effect on PFR, GFR, FF, TNa, T glucose, and QO2. N omega-methyl-L-arginine, a specific inhibitor of nitric oxide endothelium-derived relaxing factor, produced the same effect as Arg depletion.(ABSTRACT TRUNCATED AT 250 WORDS)