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The 5/6th nephrectomy or ablation/infarction (A/l) preparation has been used as a classic model of chronic kidney disease (CKD). We observed increased kidney oxygen consumption (Qo2) and altered renal hemodynamics in the A/I kidney that were normalized after combined angiotensin II (ANG II) blockade. Studies suggest hypoxia inducible factor as a protective influence in A/I. We induced hypoxia-inducible factor (HIF) and HIF target proteins by two different methods, cobalt chloride (CO[Cl.sub.2]) and dimethyloxalyglycine (DMOG), for the first week after creation of A/I and compared the metabolic and renal hemodynamic outcomes to combined ANG II blockade. We also examined the HIF target proteins expressed by using Western blots and real-time PCR. Treatment with DMOG, CO[Cl.sub.2], and ANG II blockade normalized kidney oxygen consumption factored by Na reabsorption and increased both renal blood flow and glomerular filtration rate. At 1 wk, CO[Cl.sub.2] and DMOG increased kidney expression of HIF by Western blot. In the untreated A/I kidney, VEGF, heme oxygenase-1, and GLUT1 were all modestly increased. Both ANG II blockade and CO[Cl.sub.2] therapy increased VEGF and GLUT1 but the cobalt markedly so. ANG II blockade decreased heme oxygenase-1 expression while CO[Cl.sub.2] increased it. By real-time PCR, erythropoietin and GLUT1 were only increased by CO[Cl.sub.2] therapy. Cell proliferation was modestly increased by ANG II blockade but markedly after cobalt therapy. Metabolic and hemodynamic abnormalities were corrected equally by ANG II blockade and HIF therapies. However, the molecular patterns differed significantly between ANG II blockade and cobalt therapy. HIF induction may prove to be protective in this model of CKD. vascular endothelial growth factor; subtotal nephrectomy; heme oxygenase-1; kidney oxygen consumption doi: 10.1152/ajprenal.00153.2010

Diabetic nephropathy is the commonest cause of end-stage renal disease. Inordinate kidney growth and glomerular hyperfiltration at the very early stages of diabetes are putative antecedents to this disease. The kidney is the only organ that grows larger with the onset of diabetes mellitus, yet there remains confusion about the mechanism and significance of this growth. Here we show that kidney proximal tubule cells in culture transition to senescence in response to oxidative stress. We further determine the temporal expression of [G.sub.1] phase cell cycle components in rat kidney cortex at days 4 and 10 of streptozotocin diabetes to evaluate changes in this growth response. In diabetic rats we observe increases in kidney weight-to-body weight ratios correlating with increases in expression of the growth-related proteins in the kidney at day 4 after induction of diabetes. However, at day 10 we find a decrease in this profile in diabetic animals coincident with increased cyclin-dependent kinase inhibitor expressions. We observe no change in caspase-3 expression in the diabetic kidneys at these early time points; however, diabetic animals demonstrate reduced kidney connexin 43 and increased plasminogen activator inhibitor-I expressions and increased senescence-associated 13-galactosidase activity in cortical tubules. In summary, diabetic kidneys exhibit an early temporal induction of growth phase components followed by their suppression concurrent with the induction of cyclin-dependent kinase inhibitors and markers of senescence. These data delineate a phenotypic change in cortical tubules early in the pathogenesis of diabetes that may contribute to further downstream complications of the disease. proximal tubule; hypertrophy; cyclin-dependent kinase inhibitor; connexin 43 doi: 10.1152/ajpcell.00096.2010.

After subtotal nephrectomy (STN), the remaining nephrons engage in hyperfiltration, which may be facilitated by a reduced sensitivity of the tubuloglomerular feedback (TGF) response to increased distal delivery. However, a muted TGF response would contradict the notion of remnant kidney as a prototype of angiotensin II (ANG II) excess, since ANG II normally sensitizes the TGF response and stimulates proximal reabsorption. We examined the role of ANG II as a modulator of TGF and proximal reabsorption in 7 days after STN in male rats. Single-nephron glomerular filtration rate (SNGFR) and proximal reabsorption ([J.sub.prox]) were measured in late proximal collections while perfusing Henle's loop for minimal and maximal TGF stimulation in rats treated with the angiotensin type 1 ([AT.sub.1]) receptor blocker losartan or placebo in drinking water for 7 days. Perfusion of Henle's loop yielded a robust TGF response in sham-operated rats. In STN, the feedback responses were highly variable and nil, on average. Paradoxical TGF responses to augmented late proximal flow were confirmed in SNGFR measurements from the early distal nephron. Chronic losartan treatment normalized the average TGF response without reducing the variability. [J.sub.prox] was subtly affected by chronic losartan in sham surgery or STN, after controlling for differences in SNGFR. However, when administered acutely into the early S1 segment, losartan potently suppressed [J.sub.prox] in STN and sham-operated rats alike. Chronic losartan stabilizes the TGF system in remnant kidneys. This cannot be explained by currently known actions of [AT.sub.1] receptors but is commensurate with a salutary effect of an intact TGF system on dynamic autoregulation of intraglomerular flow and pressure. proximal tubular reabsorption; glomerulotubular balance; hyperfiltration

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. nitric oxide; glomerular filtration rate; octreotide

Agmatine, decarboxylated arginine, is produced in the kidney and can increase nephron and kidney filtration rate via renal vasodilatation and increases in plasma flow. This increase in filtration rate after agmatine is prevented by administration of nitric oxide synthase (NOS) inhibitors. In endothelial cells, agmatine-stimulated nitrite production is accompanied by induction of cytosolic calcium. NOS activity requires calcium for activation; however, the source of this calcium remains unknown. Ryanodine receptor (RyR) calcium-activated calcium release channels are present in the kidney cortex, and we evaluated if RyR contributes to the agmatine response. Agmatine microperfused into Bowman's space reversibly increases nephron filtration rate (SNGFR) by [Tilde] 30%. cADP-ribose (cADPR) regulates RyR channel activity. Concurrent infusion of agmatine with the cADPR blocker 8-bromo-cADPR (2 [micro]M) prevents the increase in filtration rate. Furthermore, direct activation of the RyR channel with ryanodine at agonist concentrations (5 [micro]M) increases SNGFR, and, like agmatine, this increase is prevented by administration of [N.sup.G]-monomethyl-L-arginine, a nonselective NOS blocker. We demonstrate that agmatine does not elicit ADPR cyclase activity in vascular smooth muscle membranes and does not directly affect RyR calcium channel responses using sea urchin egg homogenates. These results imply interplay between endothelial cell cADPR/RyR/[Ca.sup.2+]/NO and the cADPR/RyR/[Ca.sup.2+] pathways in vascular smooth muscle cells in arterioles in the regulation of kidney filtration rate. In conclusion, we show that agmatine-induced effects require activation of cADPR and RyR calcium release channels for NO generation, vasodilation, and increased filtration rate. ryanodine; agmatine; glomerular filtration rate; nitric oxide

The tubuloglomerular feedback (TGF) system serves to establish an appropriate balance between tubular reabsorption and glomerular filtration rate (GFR). High salt at the macnia densa activates TGF to decrease GFR. Effector molecules for the TGF signal include ATP and adenosine. Over time, the GFR will adapt by increasing even if a high salt concentration persists. A potential modulator of this TGF adaptation is nitric oxide synthase-1-derived nitric oxide (NO). In isolated glomerular preparations, we developed a system for evaluating the effects of changing dietary salt on ecto-5'-nucleotidase (ecto-5'-NT) activity, the final enzyme in the conversion of ATP to adenosine. We found observable ecto-5'-NT activity in isolated glomeruli and that this activity can be regulated by dietary salt, with high salt increasing activity. Conversely, NO decreases ecto-5'-NT activity in glomerular preparations. Moreover, NO inhibition of ecto-5'-NT activity is suppressed in the presence of dithiothreitol, suggesting nitrosylation as a reversible, oxidative stress-sensitive mechanism. The salt-induced activation of ecto-5'-NT correlates with high salt resetting of TGF. NO inhibition of enzymatic activity could be part of the adaptive phase. adenosine; glomerular filtration rate

We have previously shown in rats that lipopolysaccharide (LPS) causes both decreased renal perfusion and kidney arginine production before nitric oxide (NO) synthesis, resulting in a >30% reduction in plasma arginine. To clarify the early phase effects of LPS, we asked the following two questions: 1) is the rapid change in renal arginine production after LPS simply the result of decreased substrate (i.e., citrulline) delivery to the kidney or due to impaired uptake and conversion and 2) is the systemic production of NO limited by plasma arginine availability after LPS? Arterial and renal vein plasma was sampled at 30-min intervals from anesthetized rats with or without citrulline or arginine (2 [micro]mol x [min.sup.-1] x [kg.sup.-1] iv) a dose with no effect on MAP, renal function, or NO production. Exogenous citrulline was quickly converted to arginine by the kidney, resulting in plasma levels similar to equimolar arginine infusion. Also, the increase in citrulline uptake resulted primarily from increased filtered load and reabsorption. In a separate series, citrulline was infused after LPS administration, verifying that citrulline uptake and conversion persists during impaired kidney function. Last, in rats given LPS, the elevation of plasma arginine had no discernable impact on mean arterial pressure, kidney function, or systemic NO production. This work demonstrates how arginine synthesis is normally 'substrate limited' and explains how impaired kidney perfusion quickly results in decreased plasma arginine. However, contrary to in vitro studies, the significant reduction in extracellular arginine during the early phase response to LPS in vivo is not functionally rate limiting for NO production. citrulline; arginase; argininosuccinate; high-performance liquid chromatography doi:10.1152/ajpregu.00873.2005

Oxygen consumed by the kidney (Q[o.sub.2]) is primarily obligated to sodium reabsorption ([T.sub.Na]). The relationship of Q[o.sub.2] to [T.sub.Na] (Q[o.sub.2]/[T.sub.Na]) may be altered by hormones and autacoids. To examine whether Q[o.sub.2]/[T.sub.Na] depends on the mechanism of sodium reabsorption, we first evaluated the effects on Q[o.sub.2] and Q[o.sub.2]/[T.sub.Na] of benzolamide (BNZ), a proximal diuretic that works by inhibiting membrane carbonic anhydrase. During BNZ infusion in anesthetized rats, Q[o.sub.2] increased by 50% despite a 25% decline in [T.sub.Na]. However, BNZ failed to increase Q[o.sub.2]/[T.sub.Na] when given along with the adenosine A1 receptor blocker, DPCPX, which inhibits basolateral Na-bicarbonate cotransport (NBC1), or EIPA, which inhibits sodium-hydrogen exchange (NHE). Incubating freshly harvested rat proximal tubules with BNZ also caused Q[o.sub.2] to increase by 62%, an effect that was prevented by blocking the apical NHE3 with S3226. Blocking NBC1 or NHE3 in the proximal tubule will have opposite effects on cell pH, but both maneuvers should reduce active chloride transport. In conclusion, inhibiting membrane carbonic anhydrase in the proximal tubule increases [Qo.sub.2] and reduces the energy efficiency of sodium reabsorption by the kidney. This is not purely due to shifting the burden of reabsorption to a more expensive site downstream from the proximal tubule. Instead, increased cost may be incurred within the proximal tubule as the result of increased active chloride transport. NaCl reabsorption; transport efficiency; proximal tubule; benzolamide; adenosine; sodium-hydrogen exchange

Lipopolysaccharide (LPS) is used experimentally to elicit the innate physiological responses observed in human sepsis. We have previously shown that LPS causes depletion of plasma arginine before inducible nitric oxide synthase (iNOS) activity, indicating that changes in arginine uptake and/or production rather than enhanced consumption are responsible. Because the kidney is the primary source of circulating arginine and renal failure is a hallmark of septicemia, we determined the time course of changes in arginine metabolism and kidney function relative to iNOS expression. LPS given intravenously to anesthetized rats caused a decrease in mean arterial blood pressure after 120 min that coincided with increased plasma nitric oxide end products (NOx) and iNOS expression in lung and liver. Interestingly, impairment of renal function preceded iNOS activity by 30-60 min and occurred in tandem with decreased renal arginine production. The baseline rate of renal arginine production was ~60 [micro]mol * [h.sup.-1] * [kg.sup.-1], corresponding to an apparent plasma half-life of ~20 min, and decreased by one-half within 60 min of LPS. Calculations based on the systemic production and clearance show that normally only 5% of kidney arginine output is destined to become nitric oxide and that inducible nitric oxide synthase; sepsis; lipopolysaccharide; ornithine

Protein intake regulates the vasodilatory function of the kidney and NMDA receptor expression. Am J Physiol Regul Integr Comp Physiol 287: R1184-R1189, 2004. First published July 8, 2004; doi: 10.1152/ajpregu.00169.2003.--Glycine infusion in normal rats causes an increase in renal plasma flow and glomerular filtration rate (GFR). Although the renal response to glycine infusion is well characterized, the mechanism initiating this vasodilation is unknown. We recently observed functionally active N-methyl-D-aspartate (NMDA) receptors in the kidney, located primarily in tubular structures. The mechanisms regulating activity of the NMDA receptor within the kidney are also unknown, as is its normal day-to-day functional role. Therefore, we hypothesize that dietary protein may impact the functional response to glycine infusion in both untreated rats and rats pretreated with angiotensin-converting enzyme (ACE) inhibitor and, furthermore, that renal NMDA receptors may be involved in the glycine response. Surprisingly, 2 wk of low-protein diet (8% protein vs. 21% protein in control diet) totally inhibited the glycine-induced vasodilation and GFR response. Associated with the absence of renal vasodilation, a significant reduction in proximal tubular reabsorption was observed during glycine infusion in low-protein-diet rats. In contrast to the disease models previously studied in our laboratory, administration of ACE inhibitors did not restore the glycine response in rats treated with low-protein diet. Western blots of normal- and low-protein-diet kidneys demonstrate that the newly described renal NMDA receptor is downregulated in rats fed a low-protein diet. Low-protein feeding results in loss of glycine-induced vasodilation and GFR responses associated with decreased renal NMDA receptor expression. Kidney NMDA receptor expression is conditioned by protein intake, and this receptor may play an important role in the kidney vasodilatory response to glycine infusion and protein feeding in rats. glycine; N-methyl-D-aspartate receptor; renal hemodynamics; dietary protein

Early diabetes as a model for testing the regulation of juxtaglomerular NOS I. Am J Physiol Renal Physiol 287: F732-F738, 2004. First published June 22, 2004; 10.1152/ajprenal.00340.2003.--Dysregulation of kidney nitric oxide synthase (NOS) I may alter renal hemodynamics in diabetes. Four types of studies were performed in anesthetized 1- to 2-wk-streptozotocin diabetic rats. 1) Glomerular filtration rate (GFR) was measured before and during NOS I blockade. Subsequent addition of nonspecific NOS blocker tested for residual NO from other isoforms. Acute systemic NOS I blockade reduced GFR only in diabetics. Nonspecific NOS blockade had no additional effect on NOS I-blocked diabetics. 2) Renal blood flow (RBF) was monitored for evidence that tubuloglomerular feedback (TGF) resets during 1 h of continuous activation with benzolamide. NOS I blockade was added to test for the role of NOS I in TGF resetting. During 1 h of TGF activation in controls, RBF initially declined and then returned to baseline. In diabetic and NOS I-blocked rats, RBF declined and remained low. 3) The ability of NOS I blockade to increase the homeostatic efficiency of TGF in diabetes was tested by micropuncture in free-flowing nephrons. The addition of NOS I blocker to the tubular fluid increased TGF efficiency in control and diabetic rats. 4) The influence of distal salt delivery on local NOS I activity was tested by micropuncture. Henle's loop was perfused at varying rates with NOS I blocker while single-nephron GFR (SNGFR) from the late proximal tubule was measured. In controls, NOS I blockade mainly reduced SNGFR when flow through Henle's loop was high. In diabetics, NOS I blockade reduced SNGFR independently of flow through Henle's loop. In conclusion, normally, salt delivered to the macula densa (MD) exerts immediate control over MD NOS I activity. In diabetes, there is ongoing overactivity of NOS I that is not regulated by MD salt. glomerular filtration; macula densa; micropuncture; nitric oxide; tubuloglomerular feedback

At the onset of diabetes mellitus, the glomerular filtration rate becomes supranormal. Discovery science has identified many abnormalities in the early diabetic kidney that apparently contribute to this phenotype. A serviceable understanding of the early diabetic kidney requires this information to fit together. It is the purpose of this article to present an archetype that explains multiple nuances of kidney function in early diabetes. We refer to this archetype as the 'tubular hypothesis of glomerular filtration.'' Its basic tenet is that strange effects of diabetes on glomerular filtration stem from primary effects on the proximal tubule or loop of Henle that impact glomerular filtration by feedback through the macula densa. This theory can explain diabetic hyperfiltration, a paradoxical effect of dietary salt on glomerular filtration rate in diabetes, and the renal response to dietary protein and amino acid infusion in diabetes. The discussion centers on the kidney as an integrated system of parts rather than on the specific cellular mechanisms that comprise those parts. tubuloglomerular feedback; glomerulotubular balance; juxtaglomerular apparatus

A study was conducted to determine the effects nitric oxide (NO) and the NO synthase-inducing cytokines, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), have on polyamine regulation. IFN-gamma and TNF-alpha induction of NO generation was found to have resulted in suppressed ornithine decarboxuylase (ODC) activity. This and other results suggest that the NO and inflammatory cytokines have the capacity to regulate both polyamine biosynthesis and transport.

Tubuloglomerular feedback activation and proximal reabsorption reduction are achieved through renal carbonic anhydrase inhibition. Tubuloglomerular feedback testing by micropuncture and videometric flow veocitometry shows resetting in free-flowing nephrons in euvolemic rats during carbionic anhydrase inhibitor benzolamide systemic infusion. Results show that decreased proximal reabsorption causes tubuloglomerular feedback rightward resetting.

The role of nitric oxide synthase (NOS) on the effects of exogenously administered agmantine on glomerular filtration rate was analyzed in isolated rat kidneys. Infusions of BHT-933 did not increase nephron filtration rate compared to the stimulatory effects of agmantine. Furthermore, agmantine exerted an opposite effect on the constitutive enzyme system involving endothelial NOS in the rat kidneys.

The effects of variations in afferent arteriolar resistance (RA) on tubuloglomerular feedback (TGF) effector response were analyzed by micropuncture experiments in free-flowing nephrons. Analysis of changes in TGF response by micropuncture and videometric flow velocitometry indicated the role of vascular elements in TGF function. Furthermore, changes in TGF response due to alterations in RA were mediated by pre- and post-glomerular elements.

The hypothesis that sustained changes in the late proximal flow of glomerular filtration can cause resetting of tubuloglomerular feedback (TGF) function was tested using Inactin-anesthetized euvolemic rats. Changes in the fractional compensation (C) of TGF were observed. Resetting of TGF function was confirmed when C recovered 70% of its original value following suppression. It was shown that a sustained increase in late proximal flow can induce TGF resetting.

The rates of glomerular filtration and proximal tubular reabsorption are decreased when the functions of endothelium-dependent nitric oxide (EDNO) are restrained by the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Injection of L-NMMA caused a reduction in the single-nephron glomerular filtration rate in control and sham surgery animals but not in rats that underwent ipsilateral surgical renal denervation (DNX). Similar observations are noticed for proximal reabsorption which is restricted by prior DNX. Therefore, the glomerular and tubular effects by nitric oxide synthase blockades require some part of renal adrenergic activity.

Experimental measurements of glomerular hemodynamics in erythrocyte-perfused and cell-free isolated rat kidneys to account for low filtration fraction (FF) in the kidney reveal that the low glomerular ultrafiltration coefficient and the transcapillary hydrostatic pressure gradient Delta-p do not cause low FF. High renal perfusion rate essential for regulating Delta-p and glomerular hydrostatic pressure cause the low FF. Erythrocyte injection revives the glomerular hemodynamics and enhances the glomerular arteriolar resistance.