Rosiglitazone treatment restores renal responsiveness to atrial natriuretic peptide in rats with congestive heart failure.

The thiazolidinedione (TZD) class of Peroxisome proliferator-activated receptor gamma agonists has restricted clinical use for diabetes mellitus due to fluid retention and potential cardiovascular risks. These side effects are attributed in part to direct salt-retaining effect of TZDs at the renal collecting duct. A recent study from our group revealed that prolonged rosiglitazone (RGZ) treatment caused no Na+/H2 O retention or up-regulation of Na+ transport-linked channels/transporters in experimental congestive heart failure (CHF) induced by surgical aorto-caval fistula (ACF). The present study examines the effects of RGZ on renal and cardiac responses to atrial natriuretic peptide (ANP), Acetylcholine (Ach) and S-Nitroso-N-acetylpenicillamine (SNAP-NO donor). Furthermore, we assessed the impact of RGZ on gene expression related to the ANP signalling pathway in animals with ACF. Rats subjected to ACF (or sham) were treated with either RGZ (30 mg/kg/day) or vehicle for 4 weeks. Cardiac chambers pressures and volumes were assessed invasively via Miller catheter. Kidney excretory and renal hemodynamic in response to ANP, Ach and SNAP were examined. Renal clearance along with cyclic guanosine monophosphate (cGMP), gene expression of renal CHF-related genes and ANP signalling in the kidney were determined. RGZ-treated CHF rats exhibited significant improvement in the natriuretic responses to ANP infusion. This 'sensitization' to ANP was not associated with increases in neither urinary cGMP nor in vitro cGMP production. However, RGZ caused down-regulation of several genes in the renal cortex (Ace, Nos3 and Npr1) and up-regulation of ACE2, Agtrla, Mme and Cftr along down-regulation of Avpr2, Npr1,2, Nos3 and Pde3 in the medulla. In conclusion, CHF+RGZ rats exhibited significant enhancement in the natriuretic responses to ANP infusion, which are known to be blunted in CHF. This 'sensitization' to ANP is independent of cGMP signalling, yet may involve post-cGMP signalling target genes such as ACE2, CFTR and V2 receptor. The possibility that TZD treatment in uncomplicated CHF may be less detrimental than thought before deserves additional investigations.

Does Thiazolidinedione therapy exacerbate fluid retention in congestive heart failure?

The ever-growing global burden of congestive heart failure (CHF) and type 2 diabetes mellitus (T2DM) as well as their co-existence necessitate that anti-diabetic pharmacotherapy will modulate the cardiovascular risk inherent to T2DM while complying with the accompanying restrictions imposed by CHF. The thiazolidinedione (TZD) family of peroxisome proliferator-activated receptor γ (PPARγ) agonists initially provided a promising therapeutic option in T2DM owing to anti-diabetic efficacy combined with pleiotropic beneficial cardiovascular effects. However, the utility of TZDs in T2DM has declined in the past decade, largely due to concomitant adverse effects of fluid retention and edema formation attributed to salt-retaining effects of PPARγ activation on the nephron. Presumably, the latter effects are potentially deleterious in the context of pre-existing fluid retention in CHF. However, despite a considerable body of evidence on mechanisms responsible for TZD-induced fluid retention suggesting that this class of drugs is rightfully prohibited from use in CHF patients, there is a paucity of experimental and clinical studies that investigate the effects of TZDs on salt and water homeostasis in the CHF setting. In an attempt to elucidate whether TZDs actually exacerbate the pre-existing fluid retention in CHF, our review summarizes the pathophysiology of fluid retention in CHF. Moreover, we thoroughly review the available data on TZD-induced fluid retention and proposed mechanisms in animals and patients. Finally, we will present recent studies challenging the common notion that TZDs worsen renal salt and water retention in CHF.

Potential early predictors for outcomes of experimental hemorrhagic shock induced by uncontrolled internal bleeding in rats.

Uncontrolled hemorrhage, resulting from traumatic injuries, continues to be the leading cause of death in civilian and military environments. Hemorrhagic deaths usually occur within the first 6 hours of admission to hospital; therefore, early prehospital identification of patients who are at risk for developing shock may improve survival. The aims of the current study were: 1. To establish and characterize a unique model of uncontrolled internal hemorrhage induced by massive renal injury (MRI), of different degrees (20-35% unilateral nephrectomy) in rats, 2. To identify early biomarkers those best predict the outcome of severe internal hemorrhage. For this purpose, male Sprague Dawley rats were anesthetized and cannulas were inserted into the trachea and carotid artery. After abdominal laparotomy, the lower pole of the kidney was excised. During 120 minutes, hematocrit, pO2, pCO2, base excess, potassium, lactate and glucose were measured from blood samples, and mean arterial pressure (MAP) was measured through arterial tracing. After 120 minutes, blood loss was determined. Statistical prediction models of mortality and amount of blood loss were performed. In this model, the lowest blood loss and mortality rate were observed in the group with 20% nephrectomy. Escalation of the extent of nephrectomy to 25% and 30% significantly increased blood loss and mortality rate. Two phases of hemodynamic and biochemical response to MRI were noticed: the primary phase, occurring during the first 15 minutes after injury, and the secondary phase, beginning 30 minutes after the induction of bleeding. A Significant correlation between early blood loss and mean arterial pressure (MAP) decrements and survival were noted. Our data also indicate that prediction of outcome was attainable in the very early stages of blood loss, over the first 15 minutes after the injury, and that blood loss and MAP were the strongest predictors of mortality.

Restoration of renal responsiveness to atrial natriuretic peptide in experimental nephrotic syndrome by albumin infusion.

BACKGROUND: The natriuretic/diuretic response to atrial natriuretic peptide (ANP), an important regulator of water and Na(+) balance, is markedly attenuated in nephrotic syndrome (NS). It has been suggested that the diminished renal responsiveness to ANP may contribute to the pathogenesis of salt retention and edema formation in NS. However, the mechanisms underlying the renal hyporesponsiveness to ANP remain largely unknown. METHODS: The acute effects of exogenous infusion of ANP (5 µg/kg + 10 µg/kg/h) were studied by clearance methodology in control rats, hypoalbuminemic rats with Adriamycin (ADR)-induced NS and in ADR-treated rats infused with hyperoncotic albumin sufficient to restore plasma albumin to normal levels. RESULTS: Administration of ANP to control rats resulted in a significant increase in urinary flow rate, absolute rate of sodium excretion (+456%) and glomerular filtration rate (GFR). Mean arterial blood pressure decreased following infusion of the peptide. In the nephrotic rats, baseline GFR and Na(+) excretion were significantly lower than in the control animals, and the renal effects of ANP were markedly blunt compared to the control animals. In contrast, the hypotensive effect of ANP in the ADR-treated rats was largely preserved. Infusion of hyperoncotic albumin prior to ANP administration reversed the decrease in baseline GFR and Na(+) excretion and completely restored the renal effects of ANP in the nephrotic rats. CONCLUSION: These findings indicate that renal hyporesponsiveness to ANP in rats with ADR-induced NS is a reversible phenomenon that appears to be of functional origin rather than reflecting permanent cellular damage.

Renal effects of a novel endogenous natriuretic agent xanthurenic acid 8-o-ß-d-glucoside in rats.

Xanthurenic acid 8-o-ß-d-glucoside is an endogenous derivative of tryptophan metabolism, isolated from urine of patients with chronic renal disease. This compound was suggested previously to act as a natriuretic hormone based on its ability to block short circuit currents in a frog skin assay and to induce a sustained natriuresis when injected into rats (C. D. Cain et al., Proc. Natl. Acad. Sci. USA 2007: 17873-17878). The present communication describes the effects of the compound on renal clearance and hemodynamic parameters in male Sprague-Dawley rats maintained on a normal salt (0.4-0.5%) diet. Intravenous administration of synthetic xanthurenic acid 8-o-ß-d-glucoside in two consecutive incremental doses (6.3 and 31.5 nmol) resulted in a significant increase (P < 0.05), in urine flow (43.91 ± 6.31 µL/min vs. 10.54 ± 2.21 µL/min), absolute rate of sodium excretion (3.99 ± 0.95 µEq/min vs. 1.15 ± µEq/min), and percentage sodium excretion (1.63 ± 0.46% vs. 0.37 ± 0.12%, peak response vs. baseline, respectively). The natriuretic/diuretic effect was associated also with a significant increase in potassium excretion. These effects were not related to changes in renal hemodynamics or in arterial blood pressure. Pretreatment with the sodium channel blocker, amiloride, completely abolished the natriuretic and kaluretic actions of the compound. Administration of the xanthurenic acid derivative caused a dose-related increase in urinary nitrite/nitrate excretion. Moreover, under chronic nitric oxide blockade by l-NG-Nitro-Arginine-Methyl-Esther (l-NAME) sodium excretion was similar in rats treated or untreated with the compound. Our data demonstrate that xanthurenic acid 8-o-ß-d-glucoside has significant diuretic/natriuretic and kaluretic properties. An intact amiloride-sensitive sodium channel is required for the renal effects of the compound. The data further suggest that the natriuretic effect is mediated in part by a nitric oxide-dependent mechanism.

Involvement of the endothelin and nitric oxide systems in the pathogenesis of renal ischemic damage in an experimental diabetic model.

AIMS: Ischemic acute kidney injury (iAKI) in experimental diabetes mellitus (DM) is associated with a rapid kidney dysfunction more than in non-diabetic rats. We hypothesize that this vulnerability is due to excessive endothelin-1 (ET-1) expression along with dysregulation of nitric oxide synthase (NOS) isoforms. The aim of the present study was to assess the impact of ischemia on renal function in diabetic rats as compared with non-diabetic rats, and to investigate the involvement of ET-1 and NO systems in the susceptibility of diabetic kidney to ischemic damage. MAIN METHODS: DM was induced by Streptozotocin. iAKI was induced by clamping of left renal artery for 30 min. Right intact kidney served as control. 48 h following ischemia, clearance protocols were applied to assess glomerular filtration rate (GFR), urinary flow (V) and sodium excretion (U(Na)V) in both kidneys. The renal effects of ABT-627, ET(A) antagonist; A192621.1, ET(B) antagonist; L-NAME, NOS non-selective inhibitor; 1400 W, inducible NOS (iNOS) inhibitor; and NPLA, neuronal NOS (nNOS) inhibitor, were assessed following ischemic renal injury in diabetic rats. KEY FINDINGS: Induction of iAKI in diabetic and non-diabetic rats caused significant reductions in GFR, V, and U(Na)V, which were greater in diabetic than non-diabetic rats. While, treatment with ABT-627 decreased V and U(Na)V, and increased GFR, A192621.1 decreased all these parameters. L-NAME, 1400 W, and NPLA improved GFR in the ischemic diabetic kidney. SIGNIFICANCE: Excessive vasoconstrictive effects of ET-1 via ET(A) and upregulation of iNOS, are partly responsible for the impaired recovery of renal function following ischemia in diabetic rats.

Renal and systemic effects of endothelin-1 in diabetic-hypertensive rats.

The Cohen-Rosenthal Diabetic Hypertensive rat (CRDH) is a unique animal model in which genetic hypertension and diabetes developed after crossbreeding of Cohen diabetic rats sensitive substrain (CDR) and spontaneously hypertensive rats (SHR). The present study examined: 1) The acute effects of ET-1 on the systemic and renal hemodynamics in CRDH rats, CDR, and SHR; 2) The expression of ET-1 and its receptors in the renal tissue of CRDH rats. Intravenous injection of ET-1 (1.0 nmol/kg) into anesthetized SHR rats resulted in a significant immediate depressor response (mean arterial pressure (MAP) decreased from 165 ± 3 to 124 ± 12 mmHg, p < 0.0001) followed by a minor hypertensive phase (MAP increased to 170 ± 2 mmHg). Simultaneously, the administration of ET-1 caused a significant decrease in renal blood flow (RBF) from 5.8 ± 0.9 ml/min to 3.2 ± 0.5 ml/min (p = 0.026). These responses were blunted in CRDH rats and CDR. Analysis of intra-renal blood flow by laser-Doppler in CRDH rats revealed that ET-1 injection caused a decrease in cortical blood flow (Δ = -12 ± 2.9%). However, in contrast to its well-known renal medullary vasodilatory effect, ET-1 produced a significant decline in the medulla blood flow (Δ = -17.5 ± 3.4%) (p = 0.0125). These findings suggest that CDR and CRDH rats have reduced sensitivity to vascular and renal action of ET-1. Furthermore, in the CRDH rats, the expected ET-1-induced medullary vasodilatation was abolished and even reversed into prolonged vasoconstriction.

Effects of chronic rosiglitazone treatment on renal handling of salt and water in rats with volume-overload congestive heart failure.

BACKGROUND: The side effects of fluid retention and edema of the thiazolidinedione (TZD) class of peroxisome proliferator-activated receptor-γ agonists limit their use in patients with congestive heart failure (CHF). The present study aims to explore whether chronic treatment with the TZD compound rosiglitazone (RGZ) is associated with worsening of salt and water retention in male Sprague-Dawley rats with aorto-caval fistula, an experimental model of volume-overload CHF. METHODS AND RESULTS: The effects of oral RGZ (30 mg/kg per day for 4 weeks) in CHF rats on plasma volume, cumulative sodium excretion, renal expression of Na(+) channels and transporters, and selected biomarkers of CHF were compared with those in CHF rats and sham-operated control rats treated with vehicle only (n=7 to 10). Additionally, the response to acute saline loading (3.5% of body weight) was evaluated after 2 weeks of treatment by renal clearance methodology. Chronic RGZ treatment caused no further increase in plasma volume compared with vehicle-treated CHF rats. Moreover, no increase in renal expression of Na(+) transport-linked channels/transporters was observed in response to RGZ. Cumulative sodium excretion was enhanced in CHF rats after RGZ and by another TZD compound, pioglitazone. In response to saline loading, RGZ-treated animals displayed a higher natriuretic/diuretic response than did vehicle-treated rats. Chronic RGZ treatment was not associated with any deterioration in selected biomarkers of CHF, whereas indices of cardiac hypertrophy and blood pressure were improved. CONCLUSIONS: Chronic RGZ treatment was not associated with worsening of fluid retention or cardiac status in rats with experimental volume-overload CHF. Rather, RGZ appeared to improve renal handling of salt and water in rats with CHF.

Aortocaval fistula in rat: a unique model of volume-overload congestive heart failure and cardiac hypertrophy.

Despite continuous progress in our understanding of the pathogenesis of congestive heart failure (CHF) and its management, mortality remains high. Therefore, development of reliable experimental models of CHF and cardiac hypertrophy is essential to better understand disease progression and allow new therapy development. The aortocaval fistula (ACF) model, first described in dogs almost a century ago, has been adopted in rodents by several groups including ours. Although considered to be a model of high-output heart failure, its long-term renal and cardiac manifestations are similar to those seen in patients with low-output CHF. These include Na+-retention, cardiac hypertrophy and increased activity of both vasoconstrictor/antinatriureticneurohormonal systems and compensatory vasodilating/natriuretic systems. Previous data from our group and others suggest that progression of cardiorenal pathophysiology in this model is largely determined by balance between opposing hormonal forces, as reflected in states of CHF decompensation that are characterized by overactivation of vasoconstrictive/Na+-retaining systems. Thus, ACF serves as a simple, cheap, and reproducible platform to investigate the pathogenesis of CHF and to examine efficacy of new therapeutic approaches. Hereby, we will focus on the neurohormonal, renal, and cardiac manifestations of the ACF model in rats, with special emphasis on our own experience.

Pharmacogenomic, physiological, and biochemical investigations on safety and efficacy biomarkers associated with the peroxisome proliferator-activated receptor-gamma activator rosiglitazone in rodents: a translational medicine investigation.

Peroxisome proliferator-activated receptor (PPAR)-gamma modulators, a class of antidiabetic drugs, have been associated with cardiovascular risks in type 2 diabetes in humans. The objective of this study was to explore possible cardiovascular risk biomarkers associated with PPAR-gamma in rodents that could provide an alert for risk to humans. Normal, myocardial infarction-induced heart failure (HF) or Zucker diabetic fatty (ZDF) rats were used. Rats (n = 5-6) were treated with either vehicle or rosiglitazone (RGZ; 3 or 45 mg/kg/day p.o.) for 4 weeks. Biomarkers for potential cardiovascular risks were assessed, including 1) ultrasound for cardiac structure and function; 2) neuroendocrine and hormonal plasma biomarkers of cardiovascular risk; 3) pharmacogenomic profiling of cardiac and renal tissue by targeted tissue low-density gene array representing ion channels and transporters, and components of the renin-angiotensin-aldosterone system; and 4) immunohistochemistry for cardiac fibrosis, hypertrophy, and inflammation (macrophages and tumor necrosis factor-alpha). HF was confirmed by increase in cardiac brain natriuretic peptide expression (p < 0.01) and echocardiography. Adequate exposure of RGZ was confirmed by pharmacokinetics (plasma drug levels) and the pharmacodynamic biomarker adiponectin. In normal or HF rats, RGZ had no negative effects on any of the biomarkers investigated. Similarly, RGZ had no significant effects on gene expression except for the increase in interleukin-6 mRNA expression in the heart and decrease in epithelial sodium channel beta in the kidney. In contrast, echocardiography showed improved cardiac structure and function after RGZ in ZDF rats. Taken together, this study suggests a limited predictive power of these preclinical models in respect to observed clinical adverse effects associated with RGZ.

Peroxisome proliferator-activated receptor alpha and alpha/gamma agonists do not cause impairment in renal function in the rat.

BACKGROUND/AIMS: Patients treated with peroxisome proliferator-activated receptor analogs (PPAR) alpha or alpha/gamma may develop a transient and reversible increase in serum creatinine, the mechanism of which remains obscure. This study evaluates whether treatment with either PPAR-alpha or -alpha/gamma analogs, fenofibrate or tesaglitazar, may cause deterioration in renal hemodynamics or exert direct tubular or glomerular nephrotoxic effects in rats. METHODS: Male Sprague-Dawley rats (300-320 g) were treated per os with fenofibrate (300 mg/kg/day), tesaglitazar (1.2 mg/kg/day) or vehicle, for 14 days. Glomerular filtration rate (GFR) and renal blood flow (RBF) were measured by inulin clearance and ultrasonic flowmetry, and cumulative excretion of sodium and creatinine were assessed. Biomarkers of glomerular and tubular injury were measured, including urinary albumin excretion and renal mRNA levels of kidney injury molecule 1 (Kim-1), lipocalin 2 (Lcn2), and osteopontin (Spp1). RESULTS: Fenofibrate and tesaglitazar improved the lipid profile, but caused no detectable decrease in GFR or RBF compared with vehicle-treated rats. Furthermore, the cumulative excretions of sodium and creatinine were not altered by the drugs. Finally, there was no significant difference between drug- and vehicle-treated groups in urinary albumin excretion or in the expression of renal injury biomarkers. CONCLUSIONS: In the rat, no direct nephrotoxic effect or deterioration in renal hemodynamics and function were observed following treatment with fenofibrate or tesaglitazar.

Nitric oxide synthase inhibition aggravates the adverse renal effects of high but not low intraabdominal pressure.

BACKGROUND: Previously, the authors demonstrated that an intraabdominal pressure (IAP) of 14 mmHg in normal rats reduced kidney function/hemodynamics. These adverse effects are related to interference with the nitric oxide (NO) system. This study was designed to compare the effects of NO synthase (NOS) inhibition on kidney function/hemodynamics during increases in IAP from 0 mmHg to 7, 10, and 14 mmHg. METHODS: The rats were divided into six groups. After an IAP of 0 (baseline), the first three groups were subjected to increasing IAPs as follows: 7 mmHg (group 1), 10 mmHg (group 2), and 14 mmHg (group 3). Each pressure was applied for 1 h, followed by a deflation period of 60 min (recovery). An additional three groups were pretreated with nitro-L: -arginine methyl ester (L: -NAME), an NOS inhibitor, before pressures of 7 mmHg (group 4), 10 mmHg (group 5) and 14 mmHg (group 6) were applied for 1 h. Urine flow rate (V), Na(+) excretion (U(Na)V), glomerular filtration rate (GFR), and renal plasma flow (RPF), were determined throughout the experiments. RESULTS: There were no significant changes in V, U(Na)V, GFR, or RPF during 7-mmHg insufflation. However, significant reductions in these parameters were observed during 10 and 14 mmHg, with V decreasing from 9.95 + or - 1.34 microl/min to 6.8 + or - 1.1 and 6.1 + or - 0.5 microl/min (p < 0.05) and U(Na)V decreasing from 1.29 + or - 0.28 to 0.43 + or - 0.32 muEq/min (p < 0.05), and 0.39 + or - 0.09 muEq/min (p < 0.05). These alterations in excretory functions were associated with considerable declines in GFR, from 1.98 + or - 0.2 to 1.05 + or - 0.18 ml/min (p < 0.05) and 0.95 + or - 0.06 ml/min (p < 0.05) and RPF from 8.66 + or - 0.62 to 3.94 + or - 0.88 ml/min (p < 0.05) and 3.08 + or - 0.71 ml/min (p < 0.05), respectively. When the animals were pretreated with L: -NAME, the adverse renal effects of an IAP of 14 mmHg, but not 10 mmHg, were substantially aggravated. CONCLUSION: Decreased renal function/perfusion is induced by IAP pressures of 10 and 14 mmHg but not 7 mmHg. Inhibition of NOS aggravates the adverse renal effects of high (14 mmHg) but not low (7 or 10 mmHg) IAP, indicating that NO deficiency may contribute to the renal dysfunction during high IAP.

Urinary excretion of endothelin receptors ET A and ET B in hypertensive patients and normotensive subjects.

BACKGROUND/AIMS: Endothelin (ET)-1 is produced by most renal cell types. Renal tubular and vascular cells express both the ET receptors ET(A) and ET(B). Since significant amounts of ET-1 of renal origin were detected in human urine, urinary ET-1 has been used as an index for the capacity of renal ET-1 production. Here, we determine the existence of additional components of the intrarenal ET system, namely the ET(A) and ET(B) receptor subtypes, in the urine of normal and hypertensive subjects. METHODS: ET(A) and ET(B) receptors were detected in urine samples that were concentrated by TCA precipitation, Speedvac or ProteoSpin. RESULTS: Analysis of the human urine extracts revealed the existence of approximately 50 and 55 kDa of immunoreactive proteins, corresponding to ET(B) and ET(A), respectively, indicating that intact ET(A) and ET(B) are excreted in the urine of healthy subjects and hypertensive patients. Normotensive and hypertensive subjects had statistically comparable ET(B) excretion normalized to creatinine (0.58 +/- 0.16 vs. 0.83 +/- 0.17 microg/mg creatinine, respectively; p = 0.304). In contrast, ET(A) excretion was higher among hypertensive subjects (0.05 +/- 0.01 vs. 0.11 +/- 0.02 microg/mg creatinine; p = 0.0451). Immunostaining of ET(A) and ET(B) in the human urinary system revealed expression of both receptors, principally in tubular cells (mainly in medullary collecting ducts) and in the bladder urothelium, and ET(A) expression in the peritubular capillaries and arterioles. Urinary ET receptors closely and inversely correlated with indices of urine concentration, suggesting that their shedding is principally affected by urine flow. CONCLUSION: ET receptors are present in human urine, conceivably originating within the urinary system. Their excretion is principally affected by urinary concentration. It remains to be determined whether urinary ET(A)/ET(B) is of physiological/pathophysiological relevance.

The biochemical pharmacology of renin inhibitors: implications for translational medicine in hypertension, diabetic nephropathy and heart failure: expectations and reality.

The renin-angiotensin-aldosterone system (RAAS) plays a dominant role in the pathophysiology of hypertension, Diabetes mellitus (DM), chronic kidney disease (CKD) and chronic heart failure (CHF). Therefore, drugs that block key components of the RAAS such as ACE inhibitors (ACEi) and angiotensin receptor blockers (ARBs) have gained wide clinical use for these indications. Despite progress, the morbidity and mortality of patients treated with ACEi or ARBs remain high. Small molecules that directly inhibit renin (DRI) and are orally active have also been developed and one such drug, aliskiren, was introduced into clinical use for treatment of hypertension in 2007. Further clinical trials aimed to expand the therapeutic use of aliskiren are in progress for CKD-DM and CHF. In this review we analyze and review the translational medicine prospects of aliskiren in respect to the biochemical pharmacology of the RAAS, the marketed RAAS modulators and the new emerging science regarding the role of prorenin, renin and renin receptors in cardiovascular biology and disease. The information already gained with aliskiren, raises questions regarding the advantages of DRIs as monotherapy compared to marketed ACEis and ARBs, their potential added value in combination with other RAAS modulators and other unproven benefits in relation to prorenin and renin receptor biology. This review will also indicate basic and clinical research needs that are critical to determine whether DRIs can provide meaningful added medical benefits over contemporary medicines that regulate the RAAS, and the need to identify patients that are more likely to benefit from DRIs and any possible long term adverse effects.

Hyperbaric oxygen treatment improves GFR in rats with ischaemia/reperfusion renal injury: a possible role for the antioxidant/oxidant balance in the ischaemic kidney.

BACKGROUND: Ischaemic kidney injury continues to play a dominant role in the pathogenesis of acute renal failure (ARF) in many surgical and medical settings. A major event in the induction of renal injury is related to the generation of oxygen-free radicals. Hyperbaric oxygen therapy (HBO) is indicated for treatment of many ischaemic events but not for ARF. Therefore, the present study examined the effects of HBO on kidney function and renal haemodynamics in rats with ischaemic ARF. METHODS: Renal ischaemia was induced by unilateral renal artery clamping (45 min) in rats. Within 24 h following ischaemia, rats were treated twice with HBO of 100% O(2) at 2.5 absolute atmospheres for 90 min each (+HBO). Untreated rats (-HBO) served as a control. Forty-eight hours later, GFR, RBF and endothelial-dependent vasorelaxation were measured. In addition, the immunoreactive staining of 4-hydroxy-2-noneal (4-HNE), a major product of endogenous lipid peroxidation, and superoxide dismutase (SOD) were assessed. RESULTS: In the -HBO group, GFR was reduced by 94% compared with the untouched normal kidney (ischaemic: 0.06 +/- 0.03 ml/min, normal: 1.02 +/- 0.13 ml). In contrast, in the +HBO group, GFR of the ischaemic kidney (0.36 +/- 0.07 ml/min) was reduced only by 68% compared with the contralateral normal kidney (1.12 +/- 0.12 ml/min). In line with these findings, HBO improved the vasodilatory response to ACh as expressed in enhancement of both total and regional renal blood flow. In addition, HBO reduced the formation of 4-HNE by 33% and 76% and increased SOD by 30% and 70% in the cortex and outer stripe region of the medulla of the ischaemic kidney, respectively. CONCLUSION: HBO attenuates the decline in GFR following renal ischaemia, and improves endothelial-dependent vasorelaxation, suggesting that treatment with HBO may be beneficial in the setting of ischaemic ARF.

Effects of novel vasopressin receptor antagonists on renal function and cardiac hypertrophy in rats with experimental congestive heart failure.

Arginine vasopressin (AVP) plays an important role in renal hemodynamic alterations, water retention, and cardiac remodeling in congestive heart failure (CHF). The present study evaluated the acute and chronic effects of vasopressin V(1a) receptor subtype (V(1a)) and vasopressin V(2) receptor subtype (V(2)) antagonists on renal function and cardiac hypertrophy in rats with CHF. The effects of acute administration of SR 49059 [(2S)1-[(2R,3S)-5-chloro-3-(2-chlorophenyl)-1-(3,4-dimethoxybenzene-sulfonyl)-3-hydroxy-2,3-dihydro-1H-indole-2-carbonyl]-pyrrolidine-2-carboxamide)] (0.1 mg/kg) and SR 121463B (1-[4-(N-tert-butylcarbamoyl)-2-methoxybenzenesulfonyl]-5-ethoxy-3-spiro-[4-(2-morpholinoethoxy)cyclohexane]indol-2-one, fumarate; equatorial isomer) (0.3 mg/kg), V(1a) and V(2) antagonists, respectively, on renal function, and of chronic treatment (3.0 mg/kg/day for 7 or 28 days, via osmotic minipumps or p.o.), on water excretion and cardiac hypertrophy were studied in rats with aortocaval fistula and control rats. CHF induction increased plasma AVP (12.8 +/- 2.5 versus 32.2 +/- 8.3 pg/ml, p < 0.05). Intravenous bolus injection of SR 121463B to controls produced dramatic diuretic response (from 5.5 +/- 0.8 to 86.3 +/- 21.9 microl/min; p < 0.01). In contrast, administration of SR 49059 did not affect urine flow. Likewise, administration of SR 121463B, but not SR 49059, to rats with CHF significantly increased urinary flow rate from 20.8 +/- 6.4 to 91.6 +/- 26.5 microl/min (p < 0.01). The diuretic effects of SR 121463B were associated with a significant decline in urinary osmolality and insignificant change of Na+ excretion. In line with its acute effects, chronic administration of SR 121463B to CHF rats increased daily urinary volume 2 to 5-fold throughout the treatment period. Both SR 121463B and SR 49059 significantly reduced heart weight in CHF rats when administered for 4 weeks, but not 1 week. These results suggest that V(2) and V(1a) antagonists improve water balance and cardiac hypertrophy in CHF and might be beneficial for the treatment of water retention and cardiac remodeling in CHF.

Adverse effects of pneumoperitoneum on renal function: involvement of the endothelin and nitric oxide systems.

Increased intra-abdominal pressure (IAP) during laparoscopy adversely affects kidney function. The mechanism underlying this phenomenon is largely unknown. This study was designed to investigate the involvement of endothelin (ET)-1 and nitric oxide (NO) systems in IAP-induced renal dysfunction. Rats were subjected to IAP of 14 mmHg for 1 h, followed by a deflation for 60 min (recovery). Four additional groups were pretreated with 1) ABT-627, an ET(A) antagonist; 2) A-192621, an ET(B) antagonist; 3) nitroglycerine; and 4) N(G)-nitro-L-arginine methyl ester, a NO synthase inhibitor, before IAP. Urine flow rate (V), absolute Na+ excretion (U(Na)V), glomerular filtration rate (GFR), and renal plasma flow (RPF) were determined. Significant reductions in kidney function and hemodynamics were observed when IAP was applied. V decreased from 8.1 +/- 1.0 to 5.8 +/- 0.5 microl/min, U(Na)V from 1.08 +/- 0.31 to 0.43 +/- 0.10 microeq/min, GFR from 1.84 +/- 0.12 to 1.05 +/- 0.06 ml/min (-46.9 +/- 2.7% from baseline), and RPF from 8.62 +/- 0.87 to 3.82 +/- 0.16 ml/min (-54 +/- 3.5% from baseline). When the animals were pretreated with either ABT-627 or A-192621, given alone or combined, the adverse effects of IAP on GFR, RPF, V, and U(Na)V were significantly augmented. When the animals were pretreated with nitroglycerine, the adverse effects of pneumoperitoneum on GFR and RPF were substantially improved. In contrast, pretreatment with N(G)-nitro-L-arginine methyl ester remarkably aggravated pneumoperitoneum-induced renal dysfunction. In conclusion, decreased renal excretory function and hypofiltration are induced by increased IAP. These effects are related to impairment of renal hemodynamics and could be partially ameliorated by pretreatment with nitroglycerine and aggravated by NO and ET blockade.

Renal and cardiac neuropeptide Y and NPY receptors in a rat model of congestive heart failure.

Neuropeptide Y (NPY) is coreleased with norepinephrine and stimulates vasoconstriction, vascular and cardiomyocyte hypertrophy via Y1 receptors (R) and angiogenesis via Y2R. Although circulating NPY is elevated in heart failure, NPY's role remains unclear. Activation of the NPY system was determined in Wistar rats with the aortocaval (A-V) fistula model of high-output heart failure. Plasma NPY levels were elevated in A-V fistula animals (115.7 +/- 15.3 vs. 63.1 +/- 17.4 pM in sham, P < 0.04). Animals either compensated [urinary Na(+) excretion returning to normal with moderate disease (COMP)] or remained decompensated with severe cardiac and renal failure (urinary Na(+) excretion <0.5 meq/day), increased heart weight, decreased mean arterial pressure and renal blood flow (RBF), and death within 5-7 days (DECOMP). Cardiac and renal tissue NPY decreased with heart failure, proportionate to the severity of renal complications. Cardiac and renal Y1R mRNA expression also decreased (1.5-fold, P < 0.005) in rats with heart failure. In contrast, Y2R expression increased up to 72-fold in the heart and 5.7-fold in the kidney (P < 0.001) proportionate to severity of heart failure and cardiac hypertrophy. Changes in receptor expression were confirmed since the Y1R agonist, [Leu31, Pro34]-NPY, had no effect on RBF, whereas the Y2R agonist (13-36)-NPY increased RBF to compensate for disease. Thus, in this model of heart failure, cardiac and renal NPY Y1 receptors decrease and Y2 receptors increase, suggesting an increased effect of NPY on the receptors involved in cardiac remodeling and angiogenesis, and highlighting an important regulatory role of NPY in congestive heart failure.

Delayed recovery of renal regional blood flow in diabetic mice subjected to acute ischemic kidney injury.

Ischemic acute kidney injury in experimental diabetes mellitus (DM) is associated with a more severe deterioration in renal function than shown in nondiabetic animals. We evaluated whether the early recovery phase from acute kidney injury is associated with a more prolonged and sustained decrease in renal perfusion in diabetic mice, which could contribute to the impaired recovery of renal function. Perfusion to the renal cortex and medulla was evaluated by laser-Doppler flowmetry in 10- to 12-wk-old anesthetized mice with type 2 DM (db/db), heterozygous mice (db/m), and nondiabetic (control) mice (C57BL/6J). After baseline measurements were obtained, the right renal artery was clampedfor 20 min followed by reperfusion for 60 min. The data demonstrated that, in all three groups studied, the reperfusion phase was characterized by a significant increase in the medullary-to-cortical blood flow ratio. Moreover, during recovery from ischemia, there was a marked prolongation in the time (in min) required to reach peak reperfusion in the cortex (db/db: 20.7 +/- 4.0, db/m: 12.92 +/- 1.9, C57BL/6J: 9.3 +/- 1.3) and the medulla (db/db: 20.8 +/- 3.2, db/m: 12.88 +/- 1.89, C57BL/6J: 11.2 +/- 1.2). Additionally, the slope of the recovery phase was lower in db/db mice (cortex: 61.9 +/- 23.1%/min, medulla: 16.3 +/- 3.6%/min) than in C57BL/6J mice (cortex: 202.2 +/- 41.6%/min, medulla: 42.1 +/- 7.2%/min). Our findings indicate that renal ischemia is associated with a redistribution of blood flow from cortex to medulla, not related to DM. Furthermore, renal ischemia in db/db mice results in a marked impairment in reperfusion of the renal cortex and medulla during the early postischemic period.

Alveolar fluid reabsorption is increased in rats with compensated heart failure.

Alveolar fluid reabsorption (AFR) is important in keeping the air spaces free of edema. This process is accomplished via active transport of Na(+) across the alveolo-capillary barrier mostly by apical Na(+) channels and basolateral Na(+)-K(+)-ATPases. Recently, we have reported that acute elevation of left atrial pressures is associated with decreased AFR in isolated rat lungs. However, the effect of chronic elevation of pulmonary capillary pressure, such as seen in patients with congestive heart failure (CHF), on AFR is unknown. CHF was induced by creating an aorto-caval fistula (ACF) in Sprague-Dawley male rats. Seven days after the placement of the fistula, AFR was studied in the isolated perfused rat lung model. AFR in control rats was 0.49 +/- 0.02 ml/h (all values are means +/- SE) and increased by approximately 40% (0.69 +/- 0.03 ml/h) in rats with chronic CHF (P < 0.001). The albumin flux from the pulmonary circulation into the air spaces did not increase in the experimental groups, indicating that lung permeability for large solutes was not increased. Na(+)-K(+)-ATPase activity and protein abundance at the plasma membrane of distal alveolar epithelial tissue were significantly increased in CHF rats compared with controls. These changes were associated with increased plasma norepinephrine levels in CHF rats compared with controls. We provide evidence that in a rat model of chronic compensated CHF, AFR is increased, possibly due to increased endogenous norepinephrine upregulating active sodium transport and protecting against alveolar flooding.