Downregulation of neuronal nitric oxide synthase in the rat remnant kidney

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Effects of Losartan, Tempol, and Their Combination On Renal Nitric Oxide Synthases in the Animal Model of Chronic Kidney Disease

Down-regulation of nitric oxide synthase (NOS) and NO deficiency in the kidneys have been implicated in the pathogenesis of chronic kidney disease (CKD). In this study we examined the effects of losartan, tempol, and combined treatment on three NOS isoforms expressions, kidney NO content and NOS correlation with renal function and structure in the early stage of adriamycin (ADR)-induced CKD in spontaneously hypertensive rats (SHR). Rats were divided into control group, and four other groups which were treated with ADR and received vehicle, losartan (L, angiotensin II type 1 receptor blocker), tempol (T, redox-cycling nitroxide) or T+L treatment (by gavage) in a six-week study. Reduction of all NOS isoforms expressions were significantly improved by losartan or tempol, and correlated with proteinuria amelioration. Combined treatment induced down-regulation of constitutive NOS isoforms, whilst inducible NOS was up-regulated and followed by increased nitrite content and a significant decline in the glomerular filtration rate. Losartan or tempol prevented ADR-induced neoexpression of vimentin in the glomeruli and tubulointerstital areas, whereas de novo vimentin expression was still observed in the atrophic tubules and in the interstitial fibroblasts and myofibroblasts in combined treatment. It can be concluded that single treatments, contrary to combined, were effective in improving NO bioavailability and slowing down the progression of CKD.

Deletion of cyclooxygenase-2 in the mouse increases arterial blood pressure with no impairment in renal NO production in response to chronic high salt intake

Experiments were designed to test the hypothesis that cyclooxygenase-2 (COX-2) activity attenuates the blood pressure increase during high NaCl intake by stimulation of endothelial nitric oxide synthase (eNOS)-mediated NO synthesis in the kidney medulla. COX-2(-/-) (C57BL6) an COX-2(+/+) mice were fed a diet with 0.004% (low salt, LS) or 4% (high salt, HS) NaCl for 18 days. Arterial blood pressure was recorded continuously using indwelling catheters. Food and water intake and diuresis were measured in metabolic cages. Urine osmolality and excretion of electrolytes, cGMP, cAMP, and NOx were determined, as well as plasma NOx and cGMP. There was a significant dependence of blood pressure on salt intake and genotype: COX-2(-/-) exhibited higher blood pressure than COX-2(+/+) both on HS and LS intake. COX-2(+/+) littermates displayed an increase in blood pressure on HS versus LS (102.3 ± 1.1 mmHg vs. 91.9 ± 0.9 mmHg) day and night. The mice exhibited significant blood pressure increases during the awake phase (night) that were larger in COX-2(-/-) on HS diet compared with COX-2(+/+). Water intake, diuresis, Na(+), and osmolyte excretions and NOx and cGMP excretions were significantly and similarly elevated with HS in COX-2(-/-) and COX-2(+/+). In summary, C57BL6 mice exhibit a salt intake-dependent increase in arterial blood pressure with increased renal NO production. COX-2 activity has a general lowering effect on arterial blood pressure. COX-2 dampens NaCl-induced increases in arterial blood pressure in the awake phase. In conclusion, COX-2 activity attenuates the changes in nocturnal blood pressure during high salt intake, and COX-2 activity is not necessary for increased renal nitric oxide formation during elevated NaCl intake.

Reduced NO production rapidly aggravates renal function through the NF-κB/ET-1/ETA receptor pathway in DOCA-salt-induced hypertensive rats

AIMS

It has been reported that endothelin-1 (ET-1) overproduction and reduced nitric oxide (NO) production are closely related to the progression of renal diseases. In the present study, we examined the interrelation between ET-1 and NO system using rats treated with the combination of deoxycorticosterone acetate (DOCA)-salt and a non selective NO synthase inhibitor N(ω)-nitro-L-arginine (NOARG).

MAIN METHODS

Rats were treated with DOCA-salt (15 mg/kg, plus drinking water containing 1% NaCl) for two weeks, and then additional treatment of NOARG (0.6 mg/ml in the drinking water) was performed for three days.

KEY FINDINGS

Combined treatment of DOCA-salt and NOARG drastically developed the severe renal dysfunction and tissue injury. This treatment additionally enhanced renal ET-1 production compared to the rats treated with DOCA-salt alone, whereas a selective ET(A) receptor antagonist ABT-627 completely prevented renal dysfunction and tissue injury. On the other hand, combined treatment of DOCA-salt and NOARG induced the phosphorylation of inhibitory protein kappa B (IκB), followed by the activation of nuclear factor-kappa B (NF-κB) in the kidney. In addition, pyrrolidine-dithiocarbamate completely suppressed not only NF-κB activation but also renal dysfunction and ET-1 overproduction.

SIGNIFICANCE

These results suggest that NF-κB/ET-1/ET(A) receptor-mediated actions are responsible for the increased susceptibility to DOCA-salt induced renal injuries in the case of reduced NO production.

eNOS gene delivery prevents hypertension and reduces renal failure and injury in rats with reduced renal mass

BACKGROUND

Impaired nitric oxide (NO) release in chronic renal failure has been implicated in the pathogenesis of hypertension and the progression of renal insufficiency. We investigated whether gene delivery of the endothelial NO synthase (eNOS) improves NO release and reduces blood pressure and renal failure and injury in rats with reduced renal mass.

METHODS

Renal failure was induced by renal artery branches ligation. Two weeks later, rats with renal failure were divided into three groups and received an intravenous injection of the vehicle or the adenovirus that expresses eNOS or β-galactosidase (β-gal). Systolic blood pressure, renal parameters and histopathology were assessed at Week 4 after gene delivery.

RESULTS

At the end of the study, systolic blood pressures, serum creatinine, proteinuria, urinary endothelin-1 (ET-1) excretion and renal cortex ET-1 levels were increased, whereas plasma and urine NO(2)/NO(3) were reduced in renal failure rats as compared to normal controls. Renal injury comprised blood vessel media hypertrophy, focal and segmental glomerular sclerosis, tubular atrophy and interstitial fibrosis. Gene delivery of eNOS, but not β-gal, prevented an increase in systolic blood pressure and proteinuria, and a reduction in plasma and urine NO(2)/NO(3). eNOS gene delivery also reduced a rise in serum creatinine, urinary ET-1 excretion and renal cortex ET-1 levels, and the renal vascular, glomerular and tubular injury.

CONCLUSION

This study indicates that eNOS gene delivery in rats with renal failure improves NO release, which likely prevents the aggravation of hypertension and slows down the progression of renal failure and injury.

Regulation of oxygen utilization by angiotensin II in chronic kidney disease

Angiotensin II blockade delays progression of chronic kidney disease by modifying intrarenal hemodynamics, but the effects on metabolic adaptations are unknown. Using the remnant kidney model of chronic kidney disease in rats, we measured the effects of combined angiotensin II blockade with captopril and losartan on renal oxygen consumption (QO(2)) and factors influencing QO(2). Remnant kidneys had proteinuria and reductions in the glomerular filtration rate (GFR), renal blood flow (RBF) and nitric oxide synthase-1 protein expression while QO(2), factored by sodium reabsorption (QO(2)/TNa), was markedly increased. Combined blockade treatment normalized these parameters while increasing sodium reabsorption but, since QO(2) was unchanged, QO(2)/TNa also normalized. Triple antihypertensive therapy, to control blood pressure, and treatment with lysine, to increase GFR and RBF, did not normalize QO(2)/TNa, suggesting a specific effect of angiotensin II in elevating QO(2)/TNa. Inhibition of nitric oxide synthase increased QO(2) in the kidney of sham-operated rats but not in the remnant kidney of untreated rats. Our study shows that combined captopril and losartan treatment normalized QO(2)/TNa and functional nitric oxide activity in the remnant kidney independent of blood pressure and GFR effects, suggesting that other mechanisms in addition to hemodynamics underlie the benefits of angiotensin II blockade.

L-arginine-induced glomerular hyperfiltration response: the roles of insulin and ANG II

Infusion of L-arginine produces an increase in glomerular filtration via kidney vasodilation, correlating with increased kidney excretion of nitric oxide (NO) metabolites, but the specific underlying mechanisms are unknown. We utilized clearance and micropuncture techniques to examine the whole kidney glomerular filtration rate (GFR) and single nephron GFR (SNGFR) responses to 1) L-arginine (ARG), 2) ARG+octreotide (OCT) to block insulin release, 3) ARG+OCT+insulin (INS) infusion to duplicate ARG-induced insulin levels, and 4) losartan (LOS), an angiotensin AT-1 receptor blocker, +ARG+OCT. ARG infusion increased GFR, while increasing insulin levels. OCT coinfusion prevented this increase in GFR, but with insulin infusion to duplicate ARG induced rise in insulin, the GFR response was restored. Identical insulin levels in the absence of ARG had no effect on GFR. In contrast to ARG infusion alone, coinfusion of OCT with ARG reduced proximal tubular fractional and absolute reabsorption potentially activating tubuloglomerular feedback. Losartan infusion, in addition to ARG and OCT (LOS+ARG+OCT), restored the increase in both SNGFR and proximal tubular reabsorption, without increasing insulin levels. In conclusion, 1) hyperfiltration responses to ARG require the concurrent, modest, permissive increase in insulin; 2) inhibition of insulin release after ARG reduces proximal reabsorption and prevents the hyperfiltration response; and 3) inhibition of ANG II activity restores the hyperfiltration response, maintains parallel increases in proximal reabsorption, and overrides the arginine/octreotide actions.

Oral sorbent AST-120 increases renal NO synthesis in uremic rats

OBJECTIVE

The urine level of nitric oxide (NO) metabolites, i.e., nitrates/nitrites (NOx), in chronic renal failure (CRF) is decreased because of reduced renal synthesis of NO. We determined whether the administration of an oral sorbent, AST-120, increases the urine level of NOx and the renal expression of nitric oxide synthase (NOS) isoforms in CRF rats.

METHODS

Chronic renal failure rats were produced by 4/5 nephrectomy. Rats were randomized into two groups: CRF control rats, and AST-120-treated CRF rats. The AST-120 was administered to the rats at a dose of 4 g/kg with powder chow for 16 weeks, whereas powder chow alone was administered to control rats. The urine levels of NOx were measured by using a NOx colorimetric assay kit. The expression of endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS) in the kidney was determined by immunohistochemistry. Serum and urine levels of indoxyl sulfate were determined by high-performance liquid chromatography.

RESULTS

Urine levels of NOx and the expression of glomerular eNOS and tubulointerstitial nNOS were significantly decreased in CRF rats compared with normal rats. The administration of AST-120 to CRF rats significantly increased urine levels of NOx and the expression of glomerular eNOS and tubulointerstitial nNOS. The administration of AST-120 to CRF rats significantly decreased urine and serum levels of indoxyl sulfate.

CONCLUSIONS

The oral sorbent AST-120 increases NO synthesis in the kidneys of uremic rats by increasing the renal expression of eNOS and nNOS, through alleviation of indoxyl sulfate overload on the kidney.

Can rodent models of diabetic kidney disease clarify the significance of early hyperfiltration?: recognizing clinical and experimental uncertainties

In the past, hyperfiltration and increased glomerular capillary pressure have been identified as important determinants of the development of DN (diabetic nephropathy). Recently, some basic research and clinical reviews on DN have omitted identifying hyperfiltration as an important risk factor. At the same time, different rodent models of DN have been described without and with documented hyperfiltration. In the present review, the importance of hyperfiltration is reassessed, reviewing key clinical and research studies, including the first single nephron studies in a mouse model of DN. From clinical studies of Type 1 and Type 2 diabetes mellitus, it is clear that many patients do not have early hyperfiltration and, even when present, its contribution to subsequent DN remains uncertain. Key mechanisms underlying hyperfiltration in rodent models are reviewed. Findings on intrarenal NO metabolism and the control of single-nephron GFR (glomerular filtration rate) in rodent models of DN are also presented. Characterization of valid experimental models of DN should include a careful delineation of the absence or presence of early hyperfiltration, with special efforts made to establish the specific role hyperfiltration may play in the emergence of DN.

Endothelin(A) (ET(A)) and ET(B) receptor-mediated regulation of nitric oxide synthase 1 (NOS1) and NOS3 isoforms in the renal inner medulla

AIM

Our laboratory and others have shown that endothelin (ET)-1 directly stimulates nitric oxide (NO) production in inner medullary collecting duct (IMCD) cells. The goal of this study was to determine which NO synthase (NOS) isoforms in IMCD are sensitive to ET-1, and the role of ET(A) and ET(B) receptor activation in vivo and in vitro.

METHODS

NOS enzymatic activity and NOS isoform protein expression were examined in cultured IMCD-3 cells and isolated renal inner medulla. ET(B) receptor-deficient homozygous rats (sl/sl) have elevated levels of circulating ET-1 and lack a functional ET(B) signalling pathway in kidneys, and furthermore provides a unique model to study ET(A) receptor signalling in the renal inner medulla in vivo.

RESULTS

Incubation of IMCD-3 cells with exogenous ET-1 (50 nm) resulted in ET(A)-dependent increased NOS1 protein expression in IMCD-3 cells with no effect on NOS2 or NOS3 expression. ET(B) receptor antagonism has no effect on NOS expression in IMCD-3 cells. Consistent with in vitro results, cytosolic NOS1 protein expression was significantly greater in the renal inner medulla of sl/sl rats compared with heterozygous (sl/+) controls, with no alteration in NOS3 expression. In contrast to protein expression data, NOS1- and NOS3-specific enzymatic activities decreased in the cytosolic fraction from the renal inner medulla of sl/sl compared with sl/+.

CONCLUSION

These results provide evidence that both ET(A) and ET(B) receptors regulate NOS isoform activity in the renal inner medulla and specifically support the hypothesis that ET(A) receptor activation increases NOS1 expression.

Influence of salt on subcellular localization of nitric oxide synthase activity and expression in the renal inner medulla

1. The aims of this study were: (i) to characterize the subcellular localization of nitric oxide synthase (NOS) 1 and NOS3 activity and expression within the cytosolic, plasma membrane and intracellular membrane subcellular fractions of the renal inner medulla of rats; and (ii) to determine whether NOS1 and NOS3 activity and expression in subcellular fractions of the renal inner medulla are regulated by dietary salt intake. Although the NOS system is important in maintaining Na(+) and water homeostasis, the identity of the NOS isoform that is sensitive to dietary Na(+) remains unclear. In addition, subcellular localization of both NOS1 and NOS3 has been shown to regulate enzymatic activity and influence the ability of NOS to produce nitric oxide (NO). 2. Renal inner medullae were dissected from male Sprague-Dawley rats and separated into cytosolic, plasma membrane and intracellular membrane fractions for measurement of NOS activity and western blot analysis. 3. On a normal-salt diet, NOS activity and NOS1 and NOS3 protein expression were present in all three subcellular fractions, although total NOS activity was enriched in the intracellular membrane fraction. In response to a high-salt diet, urinary nitrate/nitrite (NO(x)) increased. Despite an increase in NO(x) excretion, total NOS activity in the renal inner medullary homogenate was decreased. There were no detectable differences in NOS activity in the subcellular fractions. Expression of NOS1 protein was decreased in the cytoplasmic and plasma membrane fractions, although maintained in the intracellular membrane fraction, in response to high salt. Expression of NOS3 protein was unaffected by high salt. 4. In conclusion, we hypothesize that NOS1 localization in the intracellular membrane is important in increasing NO production to aid Na(+) and water homeostasis.

DOCA/NaCl-induced chronic kidney disease: a comparison of renal nitric oxide production in resistant and susceptible rat strains

Recent studies show nitric oxide (NO) deficiency is both a cause and consequence of chronic kidney disease (CKD). Reduced renal neuronal NO synthase (nNOS) abundance and activity parallel development of CKD with different models in the Sprague-Dawley (SD) rats, whereas Wistar Furth (WF) rats are protected against CKD and show preserved renal NO production. In this study, we compared renal NO in response to DOCA/salt-induced injury between the WF and SD. Studies were conducted on sham WF (n = 6) and SD (n = 6) and uninephrectized (UNX)+75 mg DOCA+1% NaCl (WF n = 9; SD n = 10) rats followed for 5 wk. Kidneys were harvested for Western blot, NOS activity, and histology. Other measurements included creatinine clearance and 24-h total NO production and urinary protein excretion. Absolute values of kidney weight were lower in WF than SD rats that showed similar percent increases with UNX+DOCA/NaCl. Proteinuria and decreased creatinine clearance were present in the SD but not the WF rats following UNX+DOCA/NaCl. Glomerular injury was mild in the WF compared with SD rats that showed many globally damaged glomeruli. Although renal nNOS abundance was decreased in both strains (higher baseline in WF), soluble NOS activity was maintained in the WF but significantly reduced in the SD rats. Renal endothelial NOS abundance and membrane NOS activity were unaffected by treatment. In summary, WF rats showed resistance to UNX+DOCA/NaCl-induced CKD with maintained renal NO production despite mild reduction in nNOS abundance. Further studies are needed to evaluate how WF rats maintain renal NO production despite similar changes in abundance as the vulnerable SD strain.

NO-independent activation of soluble guanylate cyclase prevents disease progression in rats with 5/6 nephrectomy

1. Chronic renal disease is associated with oxidative stress, reduced nitric oxide (NO) availability and soluble guanylate cyclase (sGC) dysfunction. Recently, we discovered BAY 58-2667, a compound activating heme-deficient or oxidized sGC in a NO-independent manner. 2. We assessed potential of BAY 58-2667 in preventing cardiac and renal target organ damage in rats with 5/6 nephrectomy. 3. Male Wistar rats were allocated to three groups: 5/6 nephrectomy, 5/6 nephrectomy treated with BAY 58-2667 and sham operation. Study period was 18 weeks: blood pressure and creatinine clearance were assessed repeatedly. At study end blood samples were taken and hearts and kidneys harvested for histological studies. 4. BAY 58-2667 markedly lowered blood pressure in animals with 5/6 nephrectomy (untreated versus treated animals: 189+/-14 versus 146+/-11 mmHg, P<0.001). Left ventricular weight, cardiac myocyte diameter as well as cardiac arterial wall thickness significantly decreased in comparison to untreated animals with 5/6 nephrectomy. Natriuretic peptide plasma levels were also improved by BAY 58-2667. Kidney function and morphology as assessed by creatinine clearance, glomerulosclerosis, interstitial and perivascular fibrosis of intrarenal arteries were likewise significantly improved by BAY 58-2667. 5. This is the first study showing that BAY 58-2667 effectively lowers blood pressure, reduces left ventricular hypertrophy and slows renal disease progression in rats with 5/6 nephrectomy by targeting mainly oxidized sGC. Therefore, BAY 58-2667 represents a novel pharmacological principle with potential clinical value in treatment of chronic renal disease.

Expression of nitric oxide synthase isoforms in the mouse kidney: cellular localization and influence by lipopolysaccharide and Toll-like receptor 4

We determined the cellular mRNA expression of all intrarenal nitric oxide (NO)-producing NO synthase (NOS) isoforms, endothelial NOS (eNOS) and neuronal NOS (nNOS) and inducible NOS (iNOS) in kidneys from wild-type mice (WT) and immune deficient Toll-like receptor 4 (TLR4) mutant mice, during normal physiological conditions and during a short-term (6-16 h) endotoxic condition caused by systemically administered lipopolysaccaride (LPS). Investigations were performed by means of in situ hybridization and polymerase chain reaction amplification techniques. In WT, LPS altered the expression rate of all intrarenal NOS isoforms in a differentiated but NOS-isoform coupled expression pattern, with iNOS induction, and up- and down-regulation of the otherwise constitutively expressed NOS isoforms, e.g. eNOS and nNOS and an iNOS isotype. In TLR4 mutants, LPS caused none or a lowered iNOS induction, but altered the expression rate of the constitutive NOS isoforms. It is concluded that the intrarenal spatial relation of individual NOS-isoforms and their alteration in expression provide the basis for versatile NO-mediated renal actions that may include local interactions between NOS isoforms and their individual NO-target sites, and that the NOS-isoform dependent events are regulated by TLR4 during endotoxic processes. These regulatory mechanisms are likely to participate in different pathophysiological conditions affecting NO-mediated renal functions.

Resistance to renal damage by chronic nitric oxide synthase inhibition in the Wistar-Furth rat

Chronic nitric oxide synthase inhibition (NOSI) causes chronic kidney disease (CKD) in the Sprague Dawley (SD) rat. We previously showed that the Wistar-Furth (WF) rats are resistant to several models of CKD and maintain renal nitric oxide (NO) production compared with SD rats, whereas low-dose NOSI caused progression of CKD in WF rats. Here, we evaluate the impact of high-dose chronic NOSI in WF and SD rats, as well as intrarenal responses to an acute pressor dose of NOSI in the normal WF. Rats were given N(G)-nitro-l-arginine methyl ester (l-NAME) (150 and 300 mg/l for 6-10 wk) in the drinking water after an initial bolus tail vein injection. Both strains showed significant reductions in total NO production with chronic l-NAME. SD given 150 mg/l l-NAME for 6 wk developed proteinuria and renal injury, whereas WF rats receiving 150 mg/l l-NAME for 6-10 wk or 300 mg/l for 6 wk developed no proteinuria and minimal renal injury. Blood pressure was significantly elevated with chronic NOSI in both strains but was higher in the SD rat. There was little impact on renal nitric oxide synthase expression with l-NAME, except that cortical endothelial nitric oxide synthase abundance increased in WF after 6 wk (150 mg/l). Micropuncture experiments with acute pressor NOSI resulted in similar increases in systemic blood pressure in SD and WF rats, whereas WF rats showed a much smaller increment in glomerular blood pressure compared with SD rats. In conclusion, WF rats do not develop renal injury after chronic NOSI at, or above, a dose that causes significant injury in the SD rat. This protection may be associated with protection from glomerular hypertension.

Early treatment with cGMP phosphodiesterase inhibitor ameliorates progression of renal damage

BACKGROUND

Chronic renal disease is associated with oxidative stress and reduced nitric oxide availability which, in turn, promotes hypertension and further progression of renal damage. Most actions of nitric oxide are mediated by cyclic 3',5' guanosine monophosphate (cGMP) which is rapidly degraded by phosphodiesterases (PDE). Therefore, we investigated if inhibition of PDE-5 would retard the progression of chronic renal failure.

METHODS

We studied rats with 5/6 nephrectomy treated with sildenafil (2.5 mg/kg(-1)/day(-1)) in two experimental protocols. In the first protocol, we started sildenafil therapy immediately after renal ablation and continued treatment for 8 weeks. Control groups consisted of rats with renal ablation treated with drug-free vehicle and sham-operated rats with and without sildenafil treatment.

RESULTS

In these studies, sildenafil treatment prevented hypertension and deterioration of renal function, reduced histologic damage, inflammation and apoptosis, delayed the onset of proteinuria, and preserved renal capillary integrity. In the second protocol we compared sildenafil with losartan (7.5 mg/kg(-1)/day(-1)) and the combination of both drugs in established renal disease, starting these drugs 4 weeks after 5/6 nephrectomy. Delayed sildenafil treatment failed to improve proteinuria and glomerulosclerosis but ameliorated hypertension and azotemia.

CONCLUSION

These observations suggest that currently available PDE-5 inhibitors have potential clinical value in the treatment of chronic renal disease.

Protection of wistar furth rats from chronic renal disease is associated with maintained renal nitric oxide synthase

Wistar Furth (WF) rats do not develop renal injury after severe reduction of renal mass. Because clinical and animal studies suggested that nitric oxide (NO) deficiency occurs and may contribute to chronic renal disease (CRD), the status of the NO system in WF versus Sprague Dawley (SD) rats was examined with the 5/6 renal ablation/infarction (A/I) model of CRD. Eleven weeks after A/I, SD rats developed proteinuria, severe kidney damage, decreased renal function, and marked decreases in total and renal NO synthase (NOS), specifically neuronal NOS. In contrast, WF rats exhibited elevated baseline and maintained post-A/I total NO production, with no decrease in renal cortex NOS activity despite a decrease in remnant neuronal NOS abundance. When low-dose chronic Nomega-nitro-L-arginine methyl ester treatment was added for WF A/I-treated rats, rapid progression of CRD was observed. In conclusion, elevated NO production in WF rats was associated with protection from the progression of CRD after renal mass reduction. The protection might be attributable to greater total and renal NO-generating capacity and increased nephron number, compared with SD rats. NOS inhibition rendered WF rats susceptible to progression, suggesting a possible critical threshold for NO production, below which renal injury occurs.

Protection against puromycin aminonucleoside-induced chronic renal disease in the Wistar-Furth rat

The Wistar-Furth (WF) rat is protected against chronic renal disease (CRD) following 5/6th ablation/infarction vs. the Sprague-Dawley (SD) rat, and protection was associated with preserved renal nitric oxide (NO) production. This study examined CRD induced with repeated administration of puromycin aminonucleoside (PAN). SD PAN developed nephrotic range proteinuria (>1 g/24 h), and at 15 wk severe renal injury developed and the glomerular filtration rate (GFR) was reduced to approximately 10% of sham. Total NO production, renal NO synthase (NOS) activity, and renal neuronal (n) and medullary endothelial (e)NOS abundance were reduced in the SD PAN. WF PAN exhibited less severe initial proteinuria (>400 mg/24 h), which abated within weeks, whereas GFR was normal and injury was minimal at 15 wk. Total NO production and renal NOS activity and abundance were significantly elevated compared with SD PAN. NOS mRNA (nNOS, eNOS, and inducible NOS) was not altered in WF, whereas SD showed significant increases in NOS gene expression with PAN. In conclusion, WF showed resistance to a second model of CRD with maintained renal NOS activity compared with SD.

Renal neuronal nitric oxide synthase protein expression as a marker of renal injury

BACKGROUND

Animal studies suggest that nitric oxide deficiency occurs in the remnant after 5/6 removal of renal mass. The present studies investigated the time course in relation to progression of renal disease, as well as the impact on individual renal nitric oxide synthase (NOS) isoforms.

METHODS

Rats were studied from 2 to 11 weeks after 5/6 ablation/infarction (A/I) of renal mass, with acceleration of progression by high protein and salt intake, in some groups. Measurements were made before sacrifice of 24-hour protein and creatinine excretion, blood was taken for creatinine and blood urea nitrogen (BUN) determination and the kidneys were investigated histologically for structural damage, abundance of endothelial NOS (eNOS) and neuronal NOS (nNOS), and in some groups for in vitro NOS activity.

RESULTS

A time-dependent fall in glomerular filtration rate (GFR) and rise in proteinuria and glomerular sclerosis developed after 5/6 A/I. The nNOS abundance in cortex and medulla was decreased relative to shams, in all but the mildest injury and there was a strong, steep correlation between level of glomerular sclerosis and the degree of reduction in renal nNOS. Where measured, cortical NOS activity correlated with the nNOS abundance. In contrast, the eNOS abundance was either increased or unchanged in rats post A/I.

CONCLUSION

Renal nNOS abundance was reduced in the 5/6 A/I model of renal disease when plasma creatinine> approximately 1 mg/dL and when> approximately 20% of remaining glomeruli were sclerosed.

Overexpression of angiotensin type 2 receptor ameliorates glomerular injury in a mouse remnant kidney model

Angiotensin II mediates the progression of renal disease through the type 1 receptor (AT(1)R). Recent studies have suggested that type 2 receptor (AT(2)R)-mediated signaling inhibits cell proliferation by counteracting the actions of AT(1)R. The aim of the present study was to determine the effect of AT(2)R overexpression on glomerular injury induced by (5/6) nephrectomy ((5/6)Nx). AT(2)R transgenic mice (AT(2)-Tg), overexpressing AT(2)R under the control of alpha-smooth muscle actin (alpha-SMA) promoter, and control wild-type mice (Wild) were subjected to (5/6)Nx. In AT(2)-Tg mice, the glomerular expression of AT(2)R was upregulated after (5/6)Nx. Urinary albumin excretion at 12 wk after (5/6)Nx was decreased by 33.7% in AT(2)-Tg compared with Wild mice. Glomerular size in AT(2)-Tg mice was significantly smaller than in Wild mice after (5/6)Nx (93.1 +/- 3.0 vs. 103.3 +/- 1.8 microm; P < 0.05). Immunohistochemistry revealed significant decreases in glomerular expression of platelet-derived growth factor-BB chain (PDGF-BB) and transforming growth factor-beta(1) (TGF-beta(1)) in AT(2)-Tg with (5/6)Nx compared with Wild mice. Urinary excretion of nitric oxide metabolites was increased 2.5-fold in AT(2)-Tg compared with Wild mice. EMSA showed that activation of early growth response gene-1, which induces the transcription of PDGF-BB and TGF-beta(1), was decreased in AT(2)-Tg mice. These changes in AT(2)-Tg mice at 12 wk after (5/6)Nx were blocked by the AT(2)R antagonist PD-123319. Taken together, our findings suggest that AT(2)R-mediated signaling may protect from glomerular injuries induced by (5/6)Nx and that overexpression of AT(2)R may serve as a potential therapeutic strategy for glomerular disorders.

Pregnant rats with 5/6 nephrectomy have normal volume expansion despite lower renin and kallikrein

To test the hypothesis that normal volume expansion during pregnancy is impaired during chronic renal failure, we evaluated the effects of 5/6 nephrectomy (Nx) in Sprague-Dawley rats. Partial Nx was produced by ligation of 2/3 renal arteries and contralateral Nx. Control rats had a sham operation. Four weeks later, rats were assigned to nonpregnant (n=6/each) or pregnant groups (n=11 to 12/each). At day 21, blood pressure, plasma volume, renal function, hormonal levels, and reproductive outcome were determined. Statistical analysis was performed by ANOVA, and values were expressed as mean+/-SEM. Rats with 5/6 Nx had proteinuria and lower creatinine clearance; pregnancy did not affect these parameters. Blood pressure increased in 5/6 Nx rats and was reduced by pregnancy. Both pregnant groups had lower hematocrit and higher plasma volume values (nonpregnant control, 13.4+/-0.2; nonpregnant 5/6 Nx, 14.4+/-0.2; pregnant control, 19.1+/-0.7, pregnant 5/6 Nx, 19+/-0.9 mL, P<0.001). Pregnancy increased plasma renin activity only in control rats (nonpregnant control, 2.0+/-0.7; nonpregnant 5/6 Nx, 1.6+/-1.1; pregnant control, 36.1+/-7.9, pregnant 5/6 Nx, 6.1+/-1.8 ng AI/mL per hour, P<0.001). Serum aldosterone levels were unaffected by 5/6 Nx and were higher in pregnant than in nonpregnant rats. Urinary kallikrein activity was reduced by 5/6 Nx and not changed by pregnancy (nonpregnant control, 1499+/-237; nonpregnant 5/6 Nx, 346+/-90; pregnant control, 1595+/-180, pregnant 5/6 Nx, 374+/-95 nmol/16 hours, P<0.001). No significant differences in fetal and placental weights were observed between control and 5/6 Nx rats. Present data indicate that 5/6 Nx pregnant rats were able to normally expand plasma volume despite lower renin and kallikrein levels.

Paracrine factors in tubuloglomerular feedback: adenosine, ATP, and nitric oxide

The tubuloglomerular feedback response, the change in afferent arteriolar tone caused by a change in NaCl concentration at the macula densa, is likely initiated by the generation of a vasoactive mediator within the confines of the juxtaglomerular apparatus. Substantial progress has been made in identifying the nature of this mediator and the factors that modulate its effect on vascular tone. In support of earlier studies using P1 purinergic antagonists, the application of the knockout technique has shown that adenosine 1 receptors are absolutely required for eliciting TGF responses. The background level of angiotensin II appears to be an important cofactor determining the efficiency of A1AR-induced vasoconstriction, probably through a synergistic interaction at the level of the G protein-dependent transduction mechanism. The source of the adenosine is still unclear, but it is conceivable that adenosine is generated extracellularly from released ATP through a cascade of ecto-nucleotidases. There is also evidence that ATP may activate P2 receptors in preglomerular vessels, which may contribute to autoregulation of renal vascular resistance. Nitric oxide (NO), generated by the neuronal isoform of nitric oxide synthase in macula densa cells, reduces the constrictor effect of adenosine, but the regulation of NO release and its exact role in states of TGF-induced hyperfiltration are still unclear.

Endothelin-1 in chronic renal failure and hypertension

Investigation into the role of endothelin-1 (ET-1) in renal function has revealed two major direct actions leading to the control of extracellular volume and blood pressure. These are the regulation of renal hemodynamics and glomerular filtration rate and the modulation of sodium and water excretion. In the rat remnant kidney model of chronic renal failure, ET-1 production is increased in blood vessels and renal tissues. These changes are related to an increase in preproET-1 expression and correlate with the rise in blood pressure, the development of cardiovascular hypertrophy, and the degree of renal insufficiency and injury. Selective ETA receptor blockade prevents the progression of hypertension and the vascular and renal damage, supporting a role for ET-1 in chronic renal failure progression. The increase in ET-1 production can be associated with other local mediators, including angiotensin II, transforming growth factor-beta1 and nitric oxide, the local production of which is also altered in chronic renal failure. In human patients with essential hypertension, atherosclerosis, and nephrosclerosis, plasma ET-1 levels are increased compared with patients with uncomplicated essential hypertension. Similarly, plasma ET-1 concentrations are markedly increased in patients with end-stage renal disease undergoing dialysis, and this correlates with blood pressure, suggesting that ET-1 may contribute to hypertension in these patients. The treatment of anemia in patients with renal failure with human recombinant erythropoietin increases blood pressure by accentuating the underlying endothelial dysfunction and the elevated vascular ET-1 production. Overall, these results support a role for ET-1 in hypertension and the end-organ damage associated with chronic renal failure. ETA receptor blockade may then represent a potential target for the management of hypertension and cardiovascular and renal protection.

Sexual dimorphism in the aging kidney: Effects on injury and nitric oxide system

BACKGROUND

Male gender confers enhanced susceptibility to development of age-dependent kidney damage. In other models of progressive renal disease, development of injury is linked to declines in renal nitric oxide synthase (NOS) capacity.

METHODS

We investigated the in vitro characteristics of the renal NOS system in young (3 to 5 months), middle-aged (11 to 13 months) and old (18 to 22 months) male and female Sprague-Dawley rats.

RESULTS

NOS activity (pmol [3H]-arginine converted to [3H]-citrulline/mg protein/minute) is reduced in the soluble fraction of renal cortex from old versus young males but not females. In contrast, NOS activity in the soluble fraction of cerebellum is not altered by age or gender. The abundance of endothelial NOS (eNOS) and neuronal (nNOS) is reduced in renal cortex of old versus young males but is unchanged in female cortex. In renal medulla, eNOS protein is reduced with age in both males and females. We found no difference in abundance of either eNOS or nNOS protein in the cortex of young male and female rats. The incidence and severity of glomerular damage increases markedly with age in the male and only slightly in the female.

CONCLUSION

These findings indicate that a relative reduction occurs in renal NOS in the male kidney with advancing age, whereas NOS protein and activity is maintained during aging in females. This, together with the marked age-dependent kidney damage seen in the male, suggests that the renal NO deficiency in the aging male rat may contribute to the age-dependent kidney damage.

Blunted tubuloglomerular feedback by absence of angiotensin type 1A receptor involves neuronal NOS

To define the role of angiotensin type 1A (AT1A) receptor in modulating tubuloglomerular feedback signals and to determine its relationship to neuronal NO synthase (nNOS), the diameter of the afferent arterioles of wild-type and AT1A receptor-deficient mice was measured by the blood-perfused juxtamedullary nephron technique. The afferent arteriolar diameter of wild-type and AT1A receptor-deficient mice averaged 16.7+/-0.6 (n=9) and 16.8+/-0.7 micro m (n=9), respectively. In the wild-type mice, addition of 10 micro mol/L acetazolamide to the blood perfusate exerted a biphasic afferent arteriolar constriction, with the initial response and sustained response averaging 47.2+/-3.8% and 33.9+/-3.3%, respectively. In AT1A receptor-deficient mice, the initial response and sustained response averaged 51.6+/-3.6% and 9.5+/-1.3%, respectively, and the sustained response was significantly attenuated compared with that of wild-type mice. Inhibition of nNOS with 10 micro mol/L S-methyl-L-thiocitrulline significantly decreased the afferent arteriolar diameter of AT1A receptor-deficient mice, from 15.1+/-1.2 to 5.0+/-0.3 micro m (n=7), and the decrease was significantly greater than that observed in wild-type mice (from 15.9+/-1.2 to 10.6+/-1.3 micro m; n=8). During nNOS inhibition, the initial and sustained afferent arteriolar constrictor responses to acetazolamide in wild-type mice averaged 54.4+/-6.4% and 44.8+/-11.3%; respectively, and were similar to those in AT1A receptor-deficient mice (53.2+/-6.4% and 59.5+/-4.4%, respectively). These results suggest that AT1A receptors enhance tubuloglomerular feedback-mediated afferent arteriolar constriction, at least in part, through reducing the counteracting modulation by nNOS.

Reduced nitric oxide synthase activity in rats with chronic renal disease due to glomerulonephritis

BACKGROUND

Animal studies with systemic nitric oxide synthase (NOS) inhibition and renal ablation, suggest that NO deficiency is both a cause and a consequence of chronic renal disease (CRD).

METHODS

This study examined a glomerulonephritis (GN) model of CRD to determine if NO is deficient. In addition to measuring indices of renal function (proteinuria, creatinine clearance, structural damage), indices of total and renal nitric oxide production also were assessed (total NO(X) excretion, renal NOS activity, renal NOS protein abundance, plasma levels of NOS substrate and endogenous inhibitor).

RESULTS

Rats developed increasing proteinuria 12 to 20 weeks after induction of GN (with anti-glomerular basement membrane, GBM, antibody) and at 20 weeks exhibited reduced creatinine clearances and increased glomerulosclerosis relative to age-matched controls. Total NO(X) excretion was reduced and the renal cortical NOS activity and neuronal NOS (nNOS) abundance was decreased relative to controls. There was no impact on renal or aortic endothelial NOS expression or cerebellar nNOS. The plasma l-arginine (Arg) concentration was well maintained but plasma asymmetric dimethylarginine (ADMA) concentration increased in GN versus control animals.

CONCLUSIONS

Total and renal NOS activity is reduced in the GN model of CRD due to increased circulating endogenous NOS inhibitors and decreased renal nNOS abundance.

Effect of chronic renal failure on nitric oxide metabolism

Chronic renal failure (CRF) is associated with hypertension, endothelial dysfunction, and a strong propensity for arteriosclerotic cardiovascular disease. Nitric oxide (NO) is an endogenous modulator with diverse biological functions. Chronic inhibition of NO synthases (NOS) has been shown to cause hypertension and vasculopathy. In light of these considerations, numerous studies have explored the effect of CRF on NO metabolism with the assumption that NO deficiency may be involved in the pathogenesis of cardiovascular and other consequences of uremia. The purpose of this review is to provide a brief overview of the effect of CRF on (1) the bioavailability of NO substrate, L-arginine; (2) the expression of NOS isoforms in the relevant organs; (3) the interaction of NO with reactive oxygen species that are known to be increased in CRF, and (4) the accumulation of uremic inhibitors of NOS.

Role of angiotensin II and free radicals in blood pressure regulation in a rat model of renal hypertension

One-kidney, 1-clip rats (1K1C) or uninephrectomized controls were treated with either the superoxide dismutase mimetic tempol (0.5 mmol. kg(-1). d(-1)), angiotension type 1 receptor inhibitor losartan (50 mmol. L(-1). kg(-1). d(-1)), or both (n=6 per group) for 2 weeks. At the end of the study, systolic blood pressure (BP) decreased on average by 21% in tempol-treated and 29% in losartan-treated versus untreated 1K1C (217+/-4.4 mm Hg) and was normalized in the losartan plus tempol group. Mean BP also decreased from 159+/-3.7 mm Hg in 1K1C to 93+/-2.8 mm Hg in the losartan plus tempol group. Also, aortic wall area was reduced by 18% in losartan- or tempol-treated 1K1C and by 30% in losartan plus tempol rats compared with untreated 1K1C. Plasma renin activity was increased from 4.8+/-0.3 in untreated 1K1C to 15.9+/-0.9 ng. mL(-1). h(-1) in losartan-treated but not tempol-treated 1K1C. Superoxide generation by the isolated aortic rings assessed by lucigenin chemiluminescence was significantly decreased (by approximately 40%) in all losartan, tempol, and losartan plus tempol groups compared with untreated 1K1C. Nitrotyrosine ELISA in the kidney displayed a significant reduction, from 59+/-13 ng/mg of protein in 1K1C to 12.5+/-5 ng/mg of protein in the losartan plus tempol 1K1C. Western blotting for nNOS in kidney cortex and medulla showed a protein increase in both fractions of 1K1C versus controls and was normalized by losartan plus tempol treatment. Collectively, data show a synergistic effect of losartan and tempol on BP reduction in 1K1C rats. The mechanism may involve reduced superoxide production and nitrotyrosine formation in kidney and decreased kidney neuronal-type NO synthase expression in treated animals. This status in the oxidative balance seems to affect BP in the renal hypertensive rats.

Real-time profiling of kidney tubular fluid nitric oxide concentrations in vivo

To directly determine intratubular nitric oxide concentrations ([NO]) in vivo, we modified amperometric integrated electrodes (WPI P/N ISO-NOP007), which are highly sensitive to NO and not affected by ascorbic acid, nitrite, L-arginine, or dopamine. Although reactive lengths were as short as 5 microm long, the electrode still responded rapidly. With the use of kidney surface fluid as the "zero point," the electrode tip was inserted into tubular segments along the track of a perforation made by a beveled glass pipette. The surface fluid zero point was usually stable as distal, late proximal, and early proximal tubule [NO] levels were measured sequentially in the same nephron. In eight normal rats, distal, late proximal, and early proximal [NO] concentrations were each approximately 110 nM. In contrast, in nine 5/6 nephrectomized rats 2 wk postsurgery, although [NO] also did not differ among distal, late proximal, and early proximal segments, levels were approximately fourfold higher than those in normal rats and were significantly reduced after N(G)-monomethyl-L-arginine administration. These are the first quantitative in vivo tubular fluid [NO] measurements and show a significant increase in tubular fluid [NO] after renal ablation.

Immunohistochemical localisation of neuronal nitric oxide synthase in the rainbow trout kidney

The distribution of nitrergic nervous structures in the trout kidney was studied by peroxidase-linked ABC immunostaining procedures using a polyclonal antibody raised against the neuronal isoform of nitric oxide synthase. The nitrergic plexus reaches the kidney along the vasculature, mainly running with the postcardinal vein where nitrergic fibres, microganglia like cellular clusters and isolated neurones were detected. The atubular head-kidney only showed isolated nitrergic fibres close to the larger arteries. On the other hand, the collecting tubules, collecting ducts, large arteries and glomerular arterioles of the tubular middle and posterior trunks were innervated by nitrergic fibres even though immunoreactive neurones were also observed in close apposition to some tubular elements and large arteries. These results suggest that, according to morphofunctional differences between the fish and mammalian kidneys, nitrergic neural structures may be involved in the control of particular renal functions in the rainbow trout.

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

BACKGROUND

We documented recently that increased endothelin-1 (ET-1) production in blood vessels and glomeruli of uraemic rats plays a crucial role in the development of hypertension and the progression of chronic renal failure. Normally, biological effects and local production of ET-1 are attenuated by the immediate release of nitric oxide (NO). Increasing evidence suggest, however, that NO release is impaired in chronic renal failure. We investigated whether supplementation with L-arginine, the natural precursor of NO, improves NO synthesis in uraemic rats with reduced renal mass and modulates vascular and renal ET-1 production as well as blood pressure and renal failure progression.

METHODS

One week after surgical renal mass reduction, the uraemic and sham-operated animals received either no treatment or 0.1% L-arginine in drinking water for 5 weeks. In another series of experiments, uraemic rats received 1% L-arginine for 5 weeks. Immunoreactive-ET-1 (ir-ET-1) levels in plasma, urine, and vascular and renal tissue preparations was measured by radioimmunoassay after sample extraction and purification.

RESULTS

Before treatment, systolic blood pressure was significantly elevated in uraemic animals compared to sham-operated controls (156+/-7 vs 111+/-3 mmHg, respectively; P<0.01). Thereafter, systolic blood pressure increased further in uraemic-untreated rats (systolic blood pressure at week 5; 199+/-9 mmHg, P<0.01), whereas it remained similar in uraemic rats supplemented with 0.1% L-arginine (171+/-9 mmHg, NS). At the end of the study, serum creatinine and urea, proteinuria and ir-ET-1 excretion were significantly augmented, while creatinine clearance was reduced in uraemic animals compared to the controls. Ir-ET-1 level was also increased in glomeruli as well as in thoracic aorta, mesenteric arterial bed, and pre-glomerular arteries, and was associated with vascular hypertrophy as assessed by tissue weight. In contrast, ir-ET-1 level was diminished in the renal papilla of uraemic rats. Treatment with 0.1% L-arginine significantly reduced proteinuria and urinary ir-ET-1 excretion (P<0.05) as well as ir-ET-1 level in glomeruli (P<0.01) and in thoracic aorta (P<0.05). These changes were associated with increased plasma NO metabolites NO2/NO3 levels in L-arginine-treated animals (P<0.01) and reduced aortic hypertrophy (P<0.05). In contrast, supplementation with 1% L-arginine had no effect on systolic blood pressure in uraemic rats, but exacerbated proteinuria and urinary ir-ET-1 excretion and increased serum urea (P<0.05) were observed.

CONCLUSIONS

These results indicate that improvement of NO release with a low dose but not with a high dose of L-arginine significantly attenuates the development of hypertension and the progression of renal insufficiency in rats with reduced renal mass. These protective effects may be mediated in part by the reduction of vascular and renal ET-1 production.

Nitric oxide regulates renal cortical cyclooxygenase-2 expression

We have previously shown that cyclooxygenase-2 (COX-2) is localized to the cortical thick ascending limb of the loop of Henle (cTALH)/macula densa of the rat kidney, and expression increases in response to low-salt diet and/or angiotensin-converting enzyme (ACE) inhibition. Because of the localization of neuronal nitric oxide synthase (nNOS) to macula densa and surrounding cTALH, the present study investigated the role of nitric oxide (NO) in the regulation of COX-2 expression. For in vivo studies, rats were fed a normal diet, low-salt diet or low-salt diet combined with the ACE inhibitor captopril. In each group, one-half of them were treated with the nNOS inhibitors 7-nitroinidazole (7-NI) or S-methyl-thiocitrulline. Both of these NOS inhibitors inhibited increases in COX-2 mRNA and immunoreactive protein in response to low salt and low salt+captopril. For in vitro studies, COX-2 expression was studied in primary cultures of rabbit cTALH cells immunodisssected with Tamm-Horsfall antibody. Basal COX-2 immunoreactivity expression was stimulated by S-nitroso-N-acetyl-penicillamine (SNAP), an NO donor, and intracellular cGMP concentration. The cultured cells expressed immunoreactive nNOS, and 7-NI inhibited basal COX-2 immunoreactivity expression, which could be partially overcome by cGMP. In summary, these studies indicate that NO is a mediator of increased renal cortical COX-2 expression seen in volume depletion and suggest important interactions between the NO and COX-2 systems in the regulation of arteriolar tone and the renin-angiotensin system by the macula densa.

Ontogeny of neuronal nitric oxide synthase, NOS I, in the developing porcine kidney

To determine if the developing kidney differs from the adult in the expression of the neuronal nitric oxide synthase, NOS I, these experiments measured mRNA gene expression by RNase protection assay and protein content by Western blot of NOS I in piglets at ages newborn and 3, 7, 10, 14, and 21 days and adult pigs. Whole kidney NOS I mRNA was greatest at birth and decreased progressively during renal maturation to adult levels. NOS I protein content paralleled this developmental pattern. Cortical NOS I protein was equivalent in newborn and 14-day-old piglets and was greater at both ages than the adult. Medullary NOS I protein was relatively greater than cortical in both immature ages and decreased from a peak at birth to adult levels. We conclude the following. 1) During postnatal maturation, renal NOS I mRNA and protein content show a pattern that is developmentally regulated. 2) This developmental pattern of NOS I after birth may, in part, contribute to the enhanced functional role of NO during renal maturation.

Localization of protein inhibitor of neuronal nitric oxide synthase in rat kidney

We have recently demonstrated that in rats with 5/6 nephrectomy (5/6 Nx), renal cortical and inner medullary neuronal NOS (nNOS) expression is downregulated, associated with decreased urinary excretion of nitric oxide (NO) products. Recently, a novel 89-amino acid protein [protein inhibitor of nNOS (PIN)] was isolated from rat brain and shown to inhibit nNOS activity. The present studies localized PIN in the rat kidney and determined the effect of 5/6 Nx on PIN expression. By RT-PCR, PIN mRNA was detected in the kidney cortex and inner medulla. Immunohistochemistry revealed staining for PIN in glomerular and vasa rectae endothelial cells. PIN was also localized to the apical membranes of inner medullary collecting duct (IMCD) cells. Two weeks after 5/6 Nx, inner medullary PIN expression was significantly upregulated (sham, 0.18+/-0.07 vs. 5/6 Nx, 0.58+/-0.13 arbitrary units; n = 6, P<0.02), as determined by Western blotting. In summary, our data show that PIN, a specific inhibitor of nNOS activity, is expressed in the IMCD, a site of high nNOS expression in the kidney. PIN expression is upregulated in the inner medulla of 5/6 Nx rats. Inhibition of nNOS activity by PIN may have important implications for the regulation of NO synthesis in the IMCD of normal and remnant kidneys.