Acute lung injury and acute kidney injury are established by four hours in experimental sepsis and are improved with pre, but not post, sepsis administration of TNF-α antibodies.

INTRODUCTION: Acute kidney injury (AKI) and acute lung injury (ALI) are serious complications of sepsis. AKI is often viewed as a late complication of sepsis. Notably, the onset of AKI relative to ALI is unclear as routine measures of kidney function (BUN and creatinine) are insensitive and increase late. In this study, we hypothesized that AKI and ALI would occur simultaneously due to a shared pathophysiology (i.e., TNF-α mediated systemic inflammatory response syndrome [SIRS]), but that sensitive markers of kidney function would be required to identify AKI. METHODS: Sepsis was induced in adult male C57B/6 mice with 5 different one time doses of intraperitoneal (IP) endotoxin (LPS) (0.00001, 0.0001, 0.001, 0.01, or 0.25 mg) or cecal ligation and puncture (CLP). SIRS was assessed by serum proinflammatory cytokines (TNF-α, IL-1ß, CXCL1, IL-6), ALI was assessed by lung inflammation (lung myeloperoxidase [MPO] activity), and AKI was assessed by serum creatinine, BUN, and glomerular filtration rate (GFR) (by FITC-labeled inulin clearance) at 4 hours. 20 µgs of TNF-α antibody (Ab) or vehicle were injected IP 2 hours before or 2 hours after IP LPS. RESULTS: Serum cytokines increased with all 5 doses of LPS; AKI and ALI were detected within 4 hours of IP LPS or CLP, using sensitive markers of GFR and lung inflammation, respectively. Notably, creatinine did not increase with any dose; BUN increased with 0.01 and 0.25 mg. Remarkably, GFR was reduced 50% in the 0.001 mg LPS dose, demonstrating that dramatic loss of kidney function can occur in sepsis without a change in BUN or creatinine. Prophylactic TNF-α Ab reduced serum cytokines, lung MPO activity, and BUN; however, post-sepsis administration had no effect. CONCLUSIONS: ALI and AKI occur together early in the course of sepsis and TNF-α plays a role in the early pathogenesis of both.

Interaction between vasopressin and angiotensin II in vivo and in vitro: effect on aquaporins and urine concentration.

The study was undertaken to examine the potential cross talk between vasopressin and angiotensin II (ANG II) intracellular signaling pathways. We investigated in vivo and in vitro whether vasopressin-induced water reabsorption could be attenuated by ANG II AT1 receptor blockade (losartan). On a low-sodium diet (0.5 meq/day) dDAVP-treated animals with or without losartan exhibited comparable renal function [creatinine clearance 1.2 +/- 0.1 in dDAVP+losartan (LSDL) vs. 1.1 +/- 0.1 ml.100 g(-1).day(-1) in dDAVP alone (LSD), P > 0.05] and renal blood flow (6.3 +/- 0.5 in LSDL vs. 6.8 +/- 0.5 ml/min in LSD, P > 0.05). The urine output, however, was significantly increased in LSDL (2.5 +/- 0.2 vs. 1.8 +/- 0.2 ml.100 g(-1).day(-1), P < 0.05) in association with decreased urine osmolality (2,600 +/- 83 vs. 3,256 +/- 110 mosmol/kgH(2)O, P < 0.001) compared with rats in LSD. Immunoblotting revealed significantly decreased expression of medullary AQP2 (146 +/- 6 vs. 176 +/- 10% in LSD, P < 0.01), p-AQP2 (177 +/- 13 vs. 214 +/- 12% in LSD, P < 0.05), and AQP3 (134 +/- 14 vs. 177 +/- 11% in LSD, P < 0.05) in LSDL compared with LSD. The expressions of AQP1, the alpha(1)- and gamma-subunits of Na-K-ATPase, and the Na-K-2Cl cotransporter were not different among groups. In vitro studies showed that ANG II or dDAVP treatment was associated with increased AQP2 expression and cAMP levels, which were potentiated by cotreatment with ANG II and dDAVP and were inhibited by AT1 blockade. In conclusion, ANG II AT1 receptor blockade in dDAVP-treated rats on a low-salt diet was associated with decreased urine concentration and decreased inner medullary AQP2, p-AQP2, and AQP3 expression, suggesting that AT1 receptor activation plays a significant role in regulating aquaporin expression and modulating urine concentration in vivo. Studies in collecting duct cells were confirmatory.

Combination therapy with albumin and pentoxifylline protects against acute kidney injury during endotoxemic shock in mice.

Endotoxemic shock is associated with approximately 50% incidence of acute kidney injury (AKI) and 70% mortality. Experimental studies indicate that endotoxemia-related AKI is associated with both hemodynamic and proinflammatory perturbations. We hypothesize that combined administration of albumin with pentoxifylline may protect against the development of AKI during endotoxemic shock in mice by maintaining the integrity of arterial circulation and exerting anti-inflammatory properties. We tested this hypothesis using an endotoxemic shock model produced by administering a high dose of lipopolysaccharide (LPS) (15 mg/kg intraperitoneal). LPS-treated mice developed hypotension compared to control mice (mean arterial pressure [MAP] 65.6 +/- 2.2 vs. 85.7 +/- 0.8 mm Hg, p < 0.05). Normal saline did not attenuate LPS-related hypotension (62.7 +/- 2.2 vs. 65.6 +/- 2.2 mm Hg, NS). Pentoxifylline, a phosphodiesterase inhibitor, worsened the LPS-related hypotension (50.7 +/- 6.9 vs. 65.6 +/- 2.2 mm Hg, p = 0.15) in a non-significant manner. Albumin alone caused a significant increase in MAP (79.3 +/- 4.7 vs. 62.7 +/- 2.2 mm Hg, p = 0.02), but had a non-significant modest effect on glomerular filtration rate (GFR; 60.8 +/- 24.7 vs. 38.2 +/- 18.2 microl/min, NS) compared to normal saline. However, the combination of albumin and pentoxifylline profoundly protected GFR (148.6 +/- 28.7 microl/min, vs. 38.2 +/- 18.2 microl/min, p < 0.01) as compared to normal saline. The combined administration of albumin and pentoxifylline significantly attenuated the renal iNOS protein expression and increased cardiac output. In summary, neither normal saline nor albumin nor pentoxifylline alone protected against endotoxemic shock-related AKI. However, the combination of albumin and pentoxifylline was effective in preventing AKI during endotoxemic shock. Thus, in endotoxemic shock, a multifactorial approach involving hemodynamic and anti-inflammatory effect may be necessary to decrease AKI.

Ghrelin protects mice against endotoxemia-induced acute kidney injury.

Acute kidney injury (AKI) in septic patients drastically increases the mortality to 50-80%. Sepsis is characterized by hemodynamic perturbations as well as overwhelming induction of proinflammatory cytokines. Since ghrelin has been shown to have anti-inflammatory properties, we hypothesized that ghrelin may afford renal protection during endotoxemia-induced AKI. Studies were conducted in a normotensive endotoxemia-induced AKI model in mice by intraperitoneal injection of 3.5 mg/kg LPS. Serum ghrelin levels were increased during endotoxemia accompanied by increased ghrelin receptor (GHSR-1a) protein expression in the kidney. Ghrelin administration (1.0 mg/kg sc 6 h and 30 min before and 14 h after LPS) significantly decreased serum cytokine levels (TNF-alpha, IL-1beta, and IL-6) and serum endothelin-1 levels which had been induced by LPS. The elevated serum nitric oxide (NO) levels and renal inducible NO synthase expression were also decreased by ghrelin. Renal TNF-alpha levels were also increased significantly in response to LPS and ghrelin significantly attenuated this increase. When administrated before LPS, ghrelin protected against the fall in glomerular filtration rate at 16 h (172.9 +/- 14.7 vs. 90.6 +/- 15.2 microl/min, P < 0.001) and 24 h (147.2 +/- 20.3 vs. 59.4 +/- 20.7 microl/min, P < 0.05) as well as renal blood flow at 16 h (1.65 +/- 0.07 vs. 1.47 +/- 0.04 ml/min, P < 0.01) and 24 h (1.56 +/- 0.08 vs. 1.22 +/- 0.03 ml/min, P < 0.05) after LPS administration without affecting mean arterial pressure. Ghrelin remained renal protective even when it was given after LPS. In summary, ghrelin offered significant protection against endotoxemia-induced AKI. The renal protective effect of ghrelin was associated with an inhibition of the proinflammatory cytokines. Of particular importance was the suppression of TNF-alpha both in the circulation and kidney tissues. Thus, ghrelin may be a promising peptide in managing endotoxemia-induced AKI.

Downregulation of UT-A1/UT-A3 is associated with urinary concentrating defect in glucocorticoid-excess state.

Excessive glucocorticoid hormone, as occurs with Cushing syndrome, is known to be associated with altered body water homeostasis, but the molecular mechanisms are unknown. In this study, rats treated with daily dexamethasone (Dex) for 14 d provided a model of Cushing syndrome. Compared with control rats, Dex-treated rats demonstrated increased mean arterial pressure, urine flow rate, and urinary excretion of both sodium and urea. Dex-treated rats had increased abundance of aquaporin 1 (AQP1), AQP3, and Na-K-2Cl co-transporter proteins and a marked reduction of the urea transporters UT-A1 and UT-A3. In response to an acute water load, Dex-treated rats increased water excretion more than control rats, but both groups exhibited similar AQP2 expression. In response to fluid deprivation, Dex-treated rats demonstrated an impaired urinary concentrating capacity: Urine flow rate was higher and urine osmolality was lower than control rats despite an increase in AQP1, AQP3, and Na-K-2Cl co-transporter expression. AQP2 expression was similar between the two groups, but UT-A1 and UT-A3 were decreased and urinary urea excretion was increased in Dex-treated rats. Because Dex-treated rats ingested less food and water compared with controls, paired food and water studies were performed; these substantiated the previous results. In summary, the alterations in body water observed with glucocorticoid excess may be a result, in part, of impaired urinary concentrating capacity; downregulation of UT-A1 and UT-A3 and increased urea excretion may contribute to this impairment.

Role of AQP1 in endotoxemia-induced acute kidney injury.

The effect of endotoxemia (lipopolysaccharide, 2.5 mg/kg ip) was investigated in aquaporin (AQP) 1 knockout (KO) compared with wild-type (WT) mice. At baseline, KO mice exhibited higher water intake (WI) and urine output (UO). After endotoxemia, WI and UO remained higher in the KO than WT mice, and urine osmolality was lower. The higher serum osmolality in AQP1-KO mice during endotoxemia was associated with higher AQP2 (133 +/- 8 vs. 100 +/- 3%, P < 0.01), AQP3 (140 +/- 8 vs. 100 +/- 4%, P < 0.001) and Na(+)-K(+)-2Cl(-) cotransporter type 2 (NKCC2; 152 +/- 14 vs. 100 +/- 15%, P < 0.05) expression than that in WT mice. These responses during endotoxemia in the AQP1-KO mice compared with WT were associated with lower glomerular filtration rate (GFR) (69 +/- 8 vs. 96 +/- 8 ml/min, P < 0.05) and renal blood flow (0.77 +/- 0.1 vs. 1.01 +/- 0.1 ml/min, P < 0.01). Urinary sodium excretion and fractional sodium excretion were higher in KO compared with WT mice in endotoxemia and were accompanied by more severe tubular injury. With water repletion and comparable serum osmolalities, GFR was still lower in KO (57 +/- 13 vs. 120 +/- 6 ml/min, P < 0.01) compared with WT during endotoxemia. The abundance of AQP2 and AQP3 protein in KO mice was not different from WT mice; however, NKCC2, Na(+)/H(+) exchanger type 3, and fractional sodium excretion remained higher in KO compared with WT. Thus the polyuria in AQP1-KO mice does not protect against endotoxemia-induced acute kidney injury but rather absence of AQP1 predisposed to enhanced endotoximic renal injury.

Endotoxemia-related acute kidney injury in transgenic mice with endothelial overexpression of GTP cyclohydrolase-1.

Endotoxin-related acute kidney injury has been shown to profoundly induce nitric oxide (NO), which activates sympathetic and renin-angiotensin system, resulting in renal vasoconstriction. While vascular muscle cells are known to upregulate inducible NO synthase (iNOS), less is known about the endothelium as a source of NO during endotoxemia. Studies were, therefore, undertaken both in vitro in mouse microvascular endothelial cells and in vivo in transgenic mice with overexpression of endothelial GTP cyclohydrolase, the rate-limiting enzyme for tetrahydrobiopterin, a cofactor for NO synthase. LPS significantly induced endothelial cell iNOS expression and NO concentration in the culture media, with no change in endothelial NO synthase expression. GTP cyclohydrolase-1 transgenic (Tg) mice demonstrated a significant increase in baseline urine NO-to-creatinine ratio and a more significant increase in renal iNOS expression and serum NO levels with LPS treatment compared with the wild-type (WT) mice. Glomerular filtration rate and renal blood flow decreased significantly in Tg mice with 1.0 mg/kg LPS, while no changes were observed in WT with the same dose of LPS. Serum IL-6 levels were significantly higher in Tg compared with WT mice during endotoxemia. The antioxidant tempol improved the glomerular filtration rate in the Tg mice. Thus endothelium can be an important source of iNOS and serum NO concentration during endotoxemia, thereby increasing the sensitivity to AKI. Reactive oxygen species appear to be involved in this acute renal injury in Tg mice during endotoxemia.

Molecular mechanisms of antidiuretic effect of oxytocin.

Oxytocin is known to have an antidiuretic effect, but the mechanisms underlying this effect are not completely understood. We infused oxytocin by osmotic minipump into vasopressin-deficient Brattleboro rats for five days and observed marked antidiuresis, increased urine osmolality, and increased solute-free water reabsorption. Administration of oxytocin also significantly increased the protein levels of aquaporin-2 (AQP2), phosphorylated AQP2 (p-AQP2), and AQP3 in the inner medulla and in the outer medulla plus cortex. Immunohistochemistry demonstrated increased AQP2 and p-AQP2 expression and trafficking to the apical plasma membrane of principal cells in the collecting duct, and increased AQP3 expression in the basolateral membrane. These oxytocin-induced effects were blocked by treatment with the vasopressin V2 receptor antagonist SR121463B, but not by treatment with the oxytocin receptor antagonist GW796679X. We conclude that vasopressin V2 receptors mediate the antidiuretic effects of oxytocin, including increased expression and apical trafficking of AQP2, p-AQP2, and increased AQP3 protein expression.

Prostacyclin in endotoxemia-induced acute kidney injury: cyclooxygenase inhibition and renal prostacyclin synthase transgenic mice.

Sepsis-related acute kidney injury (AKI) is the leading cause of AKI in intensive care units. Endotoxin is a primary initiator of inflammatory and hemodynamic consequences of sepsis and is associated with experimental AKI. The present study was undertaken to further examine the role of the endothelium, specifically prostacyclin (PGI(2)), in the pathogenesis of endotoxemia-related AKI. A low dose of endotoxin (LPS, 1 mg/kg) in wild-type (WT) mice was associated with stable glomerular filtration rate (GFR) (164.0 +/- 16.7 vs. 173.3 +/- 6.7 microl/min, P = not significant) as urinary excretion of 6-keto-PGF(1alpha), the major metabolite of PGI(2), increased. When cyclooxygenase inhibition with indomethacin abolished this rise in 6-keto-PGF(1alpha), the same low dose of LPS significantly decreased GFR (110.7 +/- 12.1 vs. 173.3 +/- 6.7 microl/min, P < 0.05). The same dose of indomethacin did not alter GFR in WT mice. To further study the role of PGI(2) in endotoxemia, renal-specific PGI synthase (PGIs) transgenic (Tg) mice were developed that had increased PGIs expression only in the kidney and increased urinary 6-keto-PGF(1alpha). These Tg mice, however, demonstrated endotoxemia-related AKI with low-dose LPS (1 mg/kg) (GFR: 12.6 +/- 3.9 vs. 196.5 +/- 21.0 microl/min P < 0.01), which did not alter GFR in WT mice (164.0 +/- 16.7 vs. 173.3 +/- 6.7 microl/min, P = not significant). An elevation in renal cAMP, however, suggested an activation of the PGI(2)-cAMP-renin system in these Tg mice. Moreover, angiotensin-converting enzyme inhibition afforded protection against endotoxin-related AKI in these Tg mice. Thus endothelial PGIs-mediated PGI(2), as previously shown with endothelial nitric oxide synthase-mediated nitric oxide, contributes to renal protection against endotoxemia-related AKI. This effect may be overridden by excessive activation of the renin-angiotensin system in renal-specific PGIs Tg mice.

Effect of statin and angiotensin-converting enzyme inhibition on structural and hemodynamic alterations in autosomal dominant polycystic kidney disease model.

Autosomal dominant polycystic kidney disease (ADPKD) is the most common life-threatening hereditary disease and is the fourth most common cause of end-stage kidney disease. Preclinical studies to identify effective interventions to prevent or slow progression of PKD nephropathy are therefore direly needed. Heterozygous Han:SPRD rats are an autosomal dominant PKD model with many of the characteristics of ADPKD in humans. In the present study, parameters known to antedate the decrease in renal function, namely, renal structure, renal blood flow (RBF), and mean arterial pressure (MAP), were evaluated with three different interventions, namely, HMG-CoA reductase inhibition with lovastatin, angiotensin-converting enzyme (ACE) inhibition with enalapril, and a combination of these two treatments. The statin therapy demonstrated structural and functional benefits, including increased RBF and decreased BUN, independently of a change in MAP, while the ACE inhibition therapy demonstrated structural benefit in association with a decrease in MAP. An enhancement of these protective interventions in this autosomal dominant PKD model was not demonstrated with the combined treatment.

Erythropoietin ameliorates renal dysfunction during endotoxaemia.

BACKGROUND: Sepsis has a high mortality (50-80%) when associated with acute renal failure (ARF). Oxidant injury and proinflammatory cytokines and chemokines have been shown to increase with endotoxaemia-related ARF. Since erythropoietin (EPO) has been demonstrated to possess anti-oxidant and anti-inflammatory properties, EPO may have therapeutic efficacy for treating ARF associated with endotoxaemia. METHODS: Wild-type mice were given 2.5 mg/kg of intraperitoneal (i.p.) endotoxin, lipopolysaccharide (LPS), and studied 16 h later. Thirty minutes prior to LPS, the mice were given either EPO or vehicle. RESULTS: During endotoxaemia, EPO was found to significantly attenuate the renal dysfunction, as assessed by glomerular filtration rate (48.1 +/- 12.4 microl/min vs 136.7 +/- 30.2, P < 0.05). Renal blood flow and mean arterial pressure were not significantly different between the two groups. The renal dysfunction during endotoxaemia was associated with a decrease in renal superoxide dismutase (SOD). The EPO-related renal protection was associated with reversal of the effects of endotoxin on renal SOD. CONCLUSION: This is the first demonstration of a renal protective effect of EPO on endotoxin-related renal dysfunction.

Systemic inhibition of the angiotensin-converting enzyme limits lipopolysaccharide-induced lung neutrophil recruitment through both bradykinin and angiotensin II-regulated pathways.

Recruitment of neutrophils to the lung is a sentinel event in acute lung inflammation. Identifying mechanisms that regulate neutrophil recruitment to the lung may result in strategies to limit lung damage and improve clinical outcomes. Recently, the renin angiotensin system (RAS) has been shown to regulate neutrophil influx in acute inflammatory models of cardiac, neurologic, and gastrointestinal disease. As a role for the RAS in LPS-induced acute lung inflammation has not been described, we undertook this study to examine the possibility that the RAS regulates neutrophil recruitment to the lung after LPS exposure. Pretreatment of mice with the angiotensin-converting enzyme (ACE) inhibitor enalapril, but not the anti-hypertensive hydralazine, decreased pulmonary neutrophil recruitment after exposure to LPS. We hypothesize that inhibition of LPS-induced neutrophil accumulation to the lung with enalapril occurred through both an increase in bradykinin, and a decrease in angiotensin II (ATII), mediated signaling. Bradykinin receptor blockade reversed the inhibitory effect of enalapril on neutrophil recruitment. Similarly, pretreatment with bradykinin receptor agonists inhibited IL-8-induced neutrophil chemotaxis and LPS-induced neutrophil recruitment to the lung. Inhibition of ATII-mediated signaling, with the ATII receptor 1a inhibitor losartan, decreased LPS-induced pulmonary neutrophil recruitment, and this was suggested to occur through decreased PAI-1 levels. LPS-induced PAI-1 levels were diminished in animals pretreated with losartan and in those deficient for the ATII receptor 1a. Taken together, these results suggest that ACE regulates LPS-induced pulmonary neutrophil recruitment via modulation of both bradykinin- and ATII-mediated pathways, each regulating neutrophil recruitment by separate, but distinct, mechanisms.

Pentoxifylline protects against endotoxin-induced acute renal failure in mice.

Acute renal failure (ARF) in septic patients drastically increases the mortality to 50-80%. Sepsis induces several proinflammatory cytokines including tumor necrosis factor-alpha (TNF-alpha), a major pathogenetic factor in septic ARF. Pentoxifylline has several functions including downregulation of TNF-alpha and endothelia-dependent vascular relaxation. We hypothesized that pentoxifylline may afford renal protection during endotoxemia either by downregulating TNF-alpha and/or by improving endothelial function. In wild-type mice, pentoxifylline protected against the fall in glomerular filtration rate (GFR; 105.2 +/- 6.6 vs. 50.2 +/- 6.6 microl/min, P < 0.01) at 16 h of LPS administration (2.5 mg/kg ip). This renal protective effect of pentoxifylline was associated with an inhibition of the rise in serum TNF-alpha (1.00 +/- 0.55 vs. 7.02 +/- 2.40 pg/ml, P < 0.05) and serum IL-1beta (31.3 +/- 3.6 vs. 53.3 +/- 5.9 pg/ml, P < 0.01) induced by LPS. Pentoxifylline also reversed the LPS-related increase in renal iNOS and ICAM-1 and rise in serum nitric oxide (NO). Enhanced red blood cell deformability by pentoxifylline may have increased shear rate and upregulated eNOS. Studies were therefore performed in eNOS knockout mice. The renal protection against endotoxemia with pentoxifylline was again observed as assessed by GFR (119.8 +/- 18.0 vs. 44.5 +/- 16.2 microl/min, P < 0.05) and renal blood flow (0.86 +/- 0.08 vs. 0.59 +/- 0.05 ml/min, P < 0.05). Renal vascular resistance significantly decreased with the pentoxifylline (91.0 +/- 5.8 vs. 178.0 +/- 7.6 mmHg.ml(-1).min(-1), P < 0.01). Thus pentoxifylline, an FDA-approved drug, protects against endotoxemia-related ARF and involves a decrease in serum TNF-alpha, IL-1beta, and NO as well as a decrease in renal iNOS and ICAM-1.

Hyperosmolality in vivo upregulates aquaporin 2 water channel and Na-K-2Cl co-transporter in Brattleboro rats.

There are considerable experimental results that indicate that arginine vasopressin (AVP)-independent factors are involved in urinary concentration. This study examined the role of hyperosmolality in vivo to modulate aquaporin 2 (AQP2) and Na-K-2Cl co-transporter (NKCC2), pivotal factors in urinary concentration, in AVP-deficient Brattleboro (BB) rats. Hyperglycemia with associated hyperosmolality occurred in diabetic BB rats (BBDM). Protein abundance of AQP2 increased and was reversed by insulin in the inner medulla (IM; control 100+/-5%; BBDM 146+/-8%; BBDM+Ins 122+/-9%; P<0.001) and inner stripe of outer medulla (ISOM; control 100+/-4%; BBDM 123+/-8%; BBDM+Ins 93+/-6%; P<0.05). These results were confirmed by immunohistochemistry studies. NKCC2 rose in the ISOM but was not reversed with insulin treatment. For investigation of the role of hyperosmolality in the absence of hyperglycemia on the regulation of the expression of renal AQP and NKCC2, studies were performed with hyperosmolality that was induced by 0.5% NaCl in drinking water in BB rats. Hyperosmolality that was induced by NaCl increased significantly the protein abundance of IM AQP2 (121+/-2 versus 100+/-5%; P<0.01), ISOM AQP2 (135+/-6 versus 100+/-5%; P<0.001), cortex plus outer stripe of outer medulla AQP2 (121+/-4 versus 100+/-1%; P<0.001), ISOM NKCC2 (133+/-1 versus 100+/-4%; P<0.05), and cortex plus outer stripe of outer medulla NKCC2 (142+/-16 versus 100+/-9%; P<0.05). In conclusion, hyperosmolality, secondary to either glucose or NaCl, upregulated renal AQP2 and NKCC2 in vivo in BB rats.

Ischemic acute renal failure following nephrectomy impairs long-term renal function.

Uninephrectomy is associated with increased glomerular filtration rate in both the donated and the remaining contralateral kidney. The long-term effects of ischemic acute renal failure (ARF) following uninephrectomy are unknown. This study examined renal function, histology and proteinuria 52 weeks after an episode of reversible ischemic ARF. Ischemic ARF was induced in uninephrectomised mice by renal pedicle clamping. At 52 weeks inulin clearance (muL/min/g) was 7.2+/-0.2 in sham, 5.0+/-0.1 in uninephrectomy (P<0.01 vs. sham) and 3.9+/-0.1 in uninephrectomy + ischemia (P<0.01 vs. sham, P<0.05 vs. uninephrectomy). Thus, mice subjected to uninephrectomy alone demonstrated compensatory hyperfiltration following reduction in renal mass. This response was prevented by ischemic ARF. At 52 weeks there was no difference in urine protein/creatinine, mean arterial pressure or scores of glomerulosclerosis or interstitial fibrosis. In conclusion, ischemic ARF following uninephrectomy in mice impairs long-term renal function.

Molecular analysis of impaired urinary diluting capacity in glucocorticoid deficiency.

Urinary diluting ability and protein abundance of renal aquaporins (AQPs) and ion transporters in glucocorticoid-deficient (GD) rats were examined at baseline and in response to oral water loading. Rats underwent bilateral adrenalectomy followed by aldosterone (GD) or aldosterone + dexamethasone (CTL) replacement. Before oral water loading, urinary output was significantly decreased and urinary osmolality (U(osm)) was increased in GD compared with CTL rats. Protein abundance of inner medullary AQP2 (148 +/- 18%), phosphorylated AQP2 (pAQP2, 156 +/- 13%), and AQP3 (145 +/- 8%) was significantly upregulated in GD compared with CTL rats (all P < 0.05). GD rats also demonstrated a marked reduction in urinary Na(+) excretion compared with pair-fed CTL rats. Na(+)-K(+)-2Cl(-) cotransporter, Na(+)/H(+) exchanger type 3, and cortical beta- and gamma-subunits of the epithelial Na(+) channel were significantly upregulated in GD rats. At 1 h after an acute water load (40 ml/kg by oral gavage), GD rats demonstrated a decrease in percent water excretion (5 +/- 1 vs. 33 +/- 9%, P < 0.01) and urinary output (33 +/- 12 vs. 250 +/- 65 microl x kg(-1) x min(-1), P < 0.05) and an increase in U(osm) (1,894 +/- 292 vs. 316 +/- 92 mosmol/kgH(2)O, P < 0.001) compared with CTL rats. Plasma AVP was increased (1.6 +/- 0.2 vs. 0.9 +/- 0.2 pg/ml, P < 0.05), as was protein expression of inner medullary AQP2 (149 +/- 5%) and pAQP2 (177 +/- 9%, P < 0.01), in GD compared with CTL rats; apical expression of AQP2 was maintained in GD rats. The vasopressin V(2) receptor antagonist OPC-31260 increased percent water excretion and urinary output and reduced U(osm) compared with vehicle-treated GD rats. OPC-31260 also reversed the increased abundance and apical trafficking of inner medullary AQP2 and pAQP2 protein in GD rats. In conclusion, enhanced protein abundance of Na(+) transporters and Na(+) channels with Na(+) retention occurred with GD. OPC-31260 reversed upregulation and apical trafficking of AQP2 and pAQP2 in association with improved urinary diluting capacity and increased water excretion after oral water loading.

Molecular mechanisms of impaired urinary concentrating ability in glucocorticoid-deficient rats.

The purpose of this study was to examine urinary concentrating ability and protein expression of renal aquaporins and ion transporters in glucocorticoid-deficient (GD) rats in response to water deprivation as compared with control rats. Rats underwent bilateral adrenalectomies, followed only by aldosterone replacement (GD) or both aldosterone and dexamethasone replacement (control). As compared with control rats, the GD rats demonstrated a decrease in cardiac output and mean arterial pressure. In response to 36-h water deprivation, GD rats demonstrated significantly greater urine flow rate and decreased urine osmolality as compared with control rats at comparable serum osmolality and plasma vasopressin concentrations. The initiator of the countercurrent concentrating mechanism, the sodium-potassium-2 chloride co-transporter, was significantly decreased, as was the medullary osmolality in the GD rats versus control rats. There was also a decrease in inner medulla aquaporin-2 (AQP2) and urea transporter A1 (UT-A1) in GD rats as compared with control rats. There was a decrease in outer medulla Gsalpha protein, an important factor in vasopressin-mediated regulation of AQP2. Immunohistochemistry studies confirmed the decreased expression of AQP2 and UT-A1 in kidneys of GD rats as compared with control. In summary, impairment in the urinary concentrating mechanism was documented in GD rats in association with impaired countercurrent multiplication, diminished osmotic equilibration via AQP2, and diminished urea equilibration via UT-A1. These events occurred primarily in the relatively oxygen-deficient medulla and may have been initiated, at least in part, by the decrease in mean arterial pressure and thus renal perfusion pressure in this area of the kidney.

Role of heme oxygenase-1 in endotoxemic acute renal failure.

The pathogenesis of septic acute renal failure (ARF) involves systemic vasodilation with compensatory upregulation of vasoconstrictors. This can lead to renal vasoconstriction and ARF. Heme oxygenase (HO) is the rate-limiting step in heme metabolism and produces carbon monoxide (CO) and biliverdin. HO-1 is an inducible form of the enzyme and is expressed in response to cell injury. It was hypothesized in endotoxemia, induction of HO-1 would lead to increased production of the vasodilator CO, lower blood pressure, and decrease renal function. The role of HO-1 was therefore examined in a mouse model of endotoxemia. One group of mice received LPS alone and were compared with mice that received LPS in addition to an inhibitor of HO-1, zinc protoporphyrin (ZnPP). Treatment of mice with LPS resulted in significant increases in the protein expression of HO-1 compared with controls treated with vehicle. Immunohistochemical analysis localized this upregulation to both the proximal and distal tubules as well as the vasculature. Hemodynamic studies were performed during endotoxemia and the mean arterial pressure (MAP) was found to be significantly higher in the HO-1 inhibitor-treated compared with vehicle-treated mice (78 +/- 3 vs. 64 +/- 2 mmHg, P < 0.01). It was found that the inhibitor group had higher renal blood flows (RBF) also during endotoxemia (1.8 +/- 0.2 vs. 0.68 +/- 0.1 ml/min, P < 0.01). Furthermore, when renal vascular resistance (RVR) was calculated, there was a significant decrease in RVR in the inhibitor group (43.5 +/- 3.4 vs. 95.9 +/- 11.3 mmHg.ml(-1).min(-1), P < 0.01). In concert with the hemodynamic data, glomerular filtration rate (GFR), as measured by inulin clearance, was higher in the HO inhibitor compared with the vehicle controls during endotoxemia (111.5 +/- 19.5 vs. 66.0 +/- 3.5 microl/min, P < 0.05). In summary, during endotoxemia ARF, inhibiting HO-1 with ZnPP resulted in the protection of renal function. The renal protection was associated with significantly improved systemic hemodynamics, less renal vasoconstriction, and a higher GFR.

Caspase inhibition reduces tubular apoptosis and proliferation and slows disease progression in polycystic kidney disease.

We have previously demonstrated an increase in proapoptotic caspase-3 in the kidney of Han:SPRD rats with polycystic kidney disease (PKD). The aim of the present study was to determine the effect of caspase inhibition on tubular cell apoptosis and proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 weeks of age and then treated with the caspase inhibitor IDN-8050 (10 mg/kg per day) by means of an Alzet (Palo Alto, CA) minipump or vehicle [polyethylene glycol (PEG 300)] for 5 weeks. The two-kidney/total body weight ratio more than doubled in Cy/+ rats compared with +/+ rats. IDN-8050 significantly reduced the kidney enlargement by 44% and the cyst volume density by 29% in Cy/+ rats. Cy/+ rats with PKD have kidney failure as indicated by a significant increase in blood urea nitrogen. IDN-8050 significantly reduced the increase in blood urea nitrogen in the Cy/+ rats. The number of proliferating cell nuclear antigen-positive tubular cells and apoptotic tubular cells in non-cystic and cystic tubules was significantly reduced in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. On immunoblot, the active form of caspase-3 (20 kDa) was significantly decreased in IDN-8050-treated Cy/+ rats compared with vehicle-treated Cy/+ rats. In summary, in a rat model of PKD, caspase inhibition with IDN-8050 (i) decreases apoptosis and proliferation in cystic and noncystic tubules; (ii) inhibits renal enlargement and cystogenesis, and (iii) attenuates the loss of kidney function.

Nonosmotic release of vasopressin and renal aquaporins in impaired urinary dilution in hypothyroidism.

The purpose of this study was to examine protein expression of renal aquaporins (AQP) and ion transporters in hypothyroid (HT) rats in response to an oral water load compared with controls (CTL) and HT rats replaced with l-thyroxine (HT+T). Hypothyroidism was induced by aminotriazole administration for 10 wk. Body weight, water intake, urine output, solute and urea excretion, and serum and urine osmolality were comparable among the three groups at the conclusion of the 10-wk treatment period. One hour after oral gavage of water (50 ml/kg body wt), HT rats demonstrated significantly less water excretion, higher minimal urinary osmolality, and decreased serum osmolality compared with CTL and HT+T rats. Despite the hyposmolality, plasma vasopressin concentration was elevated in HT rats. These findings in HT rats were associated with an increase in protein abundance of renal cortex AQP1 and inner medulla AQP2. AQP3, AQP4, and the Na-K-2Cl cotransporter were also increased. Moreover, 1 h following the oral water load, HT rats demonstrated a significant increase in the membrane-to-vesicle fraction of AQP2 by Western blot analysis. The defect in urinary dilution in HT rats was reversed by the V(2) vasopressin antagonist OPC-31260. In conclusion, impaired urinary dilution in HT rats is primarily compatible with the nonosmotic release of vasopressin and increased protein expression of renal AQP2. The impairment of maximal solute-free water excretion in HT rats, however, appears also to involve diminished distal fluid delivery.