Atrial natriuretic peptide protects against acute ischemic renal failure in the rat.

Because of its ability to increase glomerular filtration, antagonize the actions of vasoconstrictors, and produce vasodilation, alpha human atrial natriuretic peptide (alpha-hANP) was evaluated for its potentially beneficial effects in experimental ischemic renal failure induced by 45-60 min of renal artery occlusion in bilaterally or unilaterally renally intact Sprague-Dawley rats. After ischemia, a 4-h intrarenal infusion of alpha-hANP restored 14C-inulin clearances in bilaterally and unilaterally intact animals from 0.05 +/- 0.006 and 0.05 +/- 0.01 ml/min per 100 g to 0.314 +/- 0.04 and 0.25 +/- 0.01 ml/min per 100 g, respectively (P less than 0.001, n = 8), compared with normal values of 0.49 +/- 0.023 ml/min per 100 g. Histologically, there was a progressive decrease in medullary hyperemia and prevention of intratubular cell shedding and granulocyte margination as a result of the 4-h alpha-hANP infusion such that after 24 and 48 h the histological appearance of the tissue was essentially normal. The results show that a 4-h intrarenal infusion of alpha-hANP after renal ischemia can preserve glomerular filtration rate and reduce renal tissue damage.     

Oxygen free radicals and lungs

Some of the metabolites resulting from the monovalent reduction of O₂, superoxide anion and hydroxyl radical, are O₂ radicals, whereas H₂O₂, which is not a radical since having no unpaired electron, is also an active O₂ intermediate. These O₂ metabolites are formed intracellularly as a result of normal metabolism. Their production can increase following exposure to high O₂ concentration, radiations or certain drugs. An increased amount of extracellular O₂ metabolites occurs after activation of certain inflammatory cells or during the course of the hypoxanthine-xanthine oxidase reaction. To counteract this oxidative stress, antioxidant defenses exist, whether enzymatic (superoxide dismutase, glutathione peroxidase, catalase, etc.) or nonenzymatic (GSH, vitamin E and C, etc.). Oxidative injury can result from an imbalance between oxidative stress and the defense mechanisms. The main targets are protein, DNA and lipids. The cellular response of the lung is stereotyped and involves cell injury (especially endothelial c cells and type I pneumocytes), inflammatory reaction and repair processes.     

Oxygen free radicals and lungs

Some of the metabolites resulting from the monovalent reduction of O₂, superoxide anion and hydroxyl radical, are O₂ radicals, whereas H₂O₂, which is not a radical since having no unpaired electron, is also an active O₂ intermediate. These O₂ metabolites are formed intracellularly as a result of normal metabolism. Their production can increase following exposure to high O₂ concentration, radiations or certain drugs. An increased amount of extracellular O₂ metabolites occurs after activation of certain inflammatory cells or during the course of the hypoxanthine-xanthine oxidase reaction. To counteract this oxidative stress, antioxidant defenses exist, whether enzymatic (superoxide dismutase, glutathione peroxidase, catalase, etc.) or nonenzymatic (GSH, vitamin E and C, etc.). Oxidative injury can result from an imbalance between oxidative stress and the defense mechanisms. The main targets are protein, DNA and lipids. The cellular response of the lung is stereotyped and involves cell injury (especially endothelial c cells and type I pneumocytes), inflammatory reaction and repair processes.     

Glomerular hemodynamics in established glycerol-induced acute renal failure in the rat.

The glomerular dynamic correlates of failed filtration were studied in volume replete rats with established glycerol-induced acute renal failure (ARF). Over one-half of all nephrons formed virtually no filtrate, while the single nephron glomerular filtration rate (SNGFR) of fluid-filled nephrons, measured at the glomerulotubular junction to preclude the possibility of covert tubular leakage, averaged one-sixth of control (P less than 0.001). Even that low mean value was elevated by a few nephrons with a near normal SNGFR. Renal failure thus reflected both total filtration failure in the majority of nephrons and massively reduced filtration in most of the remainder. Glomerular capillary pressure (Pg) averaged some 14 mmHg below control (P less than 0.001), whereas the arterial colloid osmotic and Bowman's space pressures were not significantly altered. Renocortical and whole kidney blood flow were also unchanged. Marked internephron functional heterogeneity precluded estimates of the ultrafiltration coefficient. However, the fall in SNGFR correlated well with the markedly depressed Pg and afferent net filtration pressure (delta PnetA, P less than 0.001), which in turn were caused by increased preglomerular resistance and a reciprocal fall in efferent arteriolar resistance. This complex change in intrarenal resistances was largely, if not entirely, responsible for failed filtration in this ARF model.     

Progressive renal insufficiency induces increasing protection against ischemic acute renal failure

The purpose of this study was to determine whether progressive renal insufficiency alters the resistance of residual nephrons to ischemic acute renal failure. Normal rats were subjected to either sham nephrectomy (2K rats; n = 7); right nephrectomy (1K rats; n = 7); or right nephrectomy plus variable degrees of ablation (one third to three fourths) of the left kidney (less than 1K rats; n = 10). Nine additional 1K rats received varying doses of nephrotoxic antiserum (NTX rats). One week later, glomerular filtration rate was determined and then ischemic acute renal failure was induced in all remaining renal tissues (25-minute renal artery occlusion). After ischemia, glomerular filtration rate was measured for 160 minutes, renal blood flow was determined, and the kidneys were fixed by in vivo perfusion. The 2K and non-NTX 1K rats had comparable percent recoveries of glomerular filtration rate (22% +/- 5%; 23% +/- 5%) despite a 64% higher renal blood flow for the 1K group. The less than 1K rats had a significantly higher percent recovery of glomerular filtration rate (53% +/- 11%; p less than 0.01), their absolute postischemic glomerular filtration rates were comparable to those of the 2K rats, and they showed significantly less morphologic evidence of ischemic renal injury (p less than 0.01). Both NTX and non-NTX rats with renal ablation showed a strong inverse correlation between baseline glomerular filtration rate and log percent filtration rate recovery (r = -0.75, p less than 0.02; r = -0.83, p less than 0.001, respectively). The less than 1K rats (n = 6) subjected to ischemia 1 day (rather than 1 week) after renal ablation were not protected against acute renal failure (18 +/- 5%) filtration rate recovery) despite renal blood flow comparable with that in other less than 1K rats. In conclusion, progressive renal insufficiency can confer increasing protection on residual nephrons against ischemic acute renal failure once a threshold reduction in functioning renal mass is achieved (greater than 1K). The present data suggest that this protection is not a result of compensatory renal hypertrophy, increased blood flow, or increased solute excretion per nephron, but probably arises as a delayed consequence of renal insufficiency-induced alterations of the internal milieu.     

Inner medullary collecting duct function in ischemic acute renal failure

Inner medullary collecting duct function in ischemic acute renal failure: The purpose of this study was to determine the role of the medullary collecting duct in the increased urine sodium concentration, decreased urine osmolality, and altered potassium excretion with hyperkalemia which are characteristic of ischemic acute renal failure. Microcatheterization of the inner medullary collecting duct (0.1 to 5 mm from papillary tip) was carried out in rats 24 h after bilateral renal artery clamping for 45 min (n = 8) or sham-operated (n = 8). In ischemic acute renal failure (ARF), tubular fluid osmolality did not increase significantly along the inner medullary collecting duct (IMCD). Tubular fluid sodium concentration was similar to controls at the beginning of the IMCD but was significantly higher at the papillary tip. Tubular fluid to plasma potassium concentration ratio (TF/PK) increased to a greater extent along the IMCD in ischemic ARF than in controls. During acute KCl loading in two additional groups, tubular fluid potassium concentration and TF/PK were much lower at the beginning of the IMCD in ischemic ARF than in controls but increased similarly along the IMCD. In ischemic ARF, with or without KCl loading, renal tissue electrolytes showed reduced potassium concentration in the outer medullary region. The results indicate that impaired IMCD function contributes significantly to the increase in urine sodium concentration and the decrease in urine osmolality which are characteristic of ischemic acute renal failure. In ischemic ARF with mild hyperkalemia, an adaptive increase in K secretion occurred in the IMCD. Severe hyperkalemia and decreased potassium excretion during acute potassium loading in ischemic ARF were determined in more proximal nephron segments and were associated with decreased outer medullary tissue potassium, presumably due to tubular necrosis. Decreased outer medullary tissue potassium could contribute to hyperkalemia by diminishing K secretion in the pars rectae and descending limbs or in the cortical and outer medullary collecting ducts.     

HgCl2-induced acute renal failure in the Goldblatt rat

These experiments were designed to test the hypothesis that renal renin is an important determinant of the severity of acute renal failure in rats. Two-kidney "Goldblatt rats" were prepared by constricting the left renal arteries with silver clips and leaving the contralateral arteries untouched. After 2 to 5 weeks, the clips were removed, and HgCl2 was injected in 13 rats (1 ml/kg body weight of 4.7 mg of HgCl2 per milliliter of 140 mM NaCl). These rats exhibited the characteristic features of acute renal failure 24 hr later. As compared with a group of seven similarly treated rats injected with 140 mM NaCl without HgCl2, GFR, V, and UNaV were reduced, and %FE H2O and %FE Na were increased. As assessed by these parameters, severity of functional impairment was equal in both kidneys. However, cortical renin was 28 times higher in the left kidney than in the right. These results are inconsistent with the hypothesis.     

二甲氧乙二酰甘氨酸对缺血性急性肾衰竭小鼠的保护作用

目的 观察二甲氧乙二酰甘氨酸(DMOG)对小鼠缺血性急性肾衰竭的影响及其与低氧诱导因子1α(HIF-1α)活化之间的关系.方法 雄性C57/BL小鼠25只,随机分为5组:正常对照组(Control组),DMOG组(20 mg/kg,ip),假手术组(Sham组)及肾缺血-再灌注组(I/R组)和DMOG预处理组(DMOG+I/R组).采用夹闭双侧肾蒂30 min的方法建立小鼠缺血性急性.肾衰竭模型,DMOG注射6 h或缺血-再灌注24 h后采血并处死小鼠,全自动生化分析仪检测小鼠的肾功能,通过HE染色对肾组织病理学进行评分,免疫组织化学染色检测肾组织中波形蛋白的表达,TUNEL法检测细胞凋亡,Western blot方法检测肾HIF-1α活化情况.结果 DMOG组小鼠肾组织中HIF-1α的表达明显高于正常对照组(P＜0.01);DMOG+I/R组小鼠.肾功能病理学评分明显低于I/R未处理组[BUN,(26.3±6.5) vs (65.8±2.6);Scr,(27.0±14.1) vs (229.5±11.2),P＜0.01],DMOG+I/R组细胞凋亡程度和小管波形蛋白的表达较I/R组明显减少[(5.7±1.5) vs (23.3±2.1),P＜0.05;(12.9±5.7) vs (69.6±22.7),P＜0.01].结论 DMOG可通过诱导HIF-1α活化对缺血性急性肾衰竭小鼠发挥保护作用.     

Response to growth hormone therapy in experimental ischemic acute renal failure

In acute renal failure (ARF), the gene and peptide expression of insulin-like growth factor-I (IGF-I) falls. Because IGF-I is regulated by growth hormone (GH) and because kidney GH receptor expression is also attenuated in ARF, the impaired IGF-I expression may partly reflect local GH resistance. Because IGF-I treatment accelerates recovery from ARF, we determined whether high-dose GH therapy could overcome this putative GH resistance, stimulate IGF-I production, and enhance recovery. Rats with ARF were given 2.5 mg GH or vehicle (V) over 2 days, beginning 24 hours before the onset of ARF. GH prevented weight loss but did not modify the course of ARF. Next we determined whether the failure of GH to modify kidney recovery could reflect a failure to stimulate renal IGF-I gene expression. Rats were treated with GH or V over an 18-hour period beginning 1 day after the induction of ARF. Hepatic IGF-I mRNA and serum IGF-I peptide levels rose significantly with GH treatment, but the low kidney IGF-I mRNA levels did not respond. We conclude that the failure of GH to enhance recovery from ARF is caused by impaired GH-stimulated renal IGF-I production, while the maintenance of body weight likely reflects the systemic effects of the increase in hepatic IGF-I production.     

Protective effect of heme oxygenase induction in ischemic acute renal failure

OBJECTIVE: To examine the role of heme oxygenase-1 (HO-1) induction in the recovery of renal function in rats with ischemic acute renal failure. DESIGN: Randomized, masked, controlled animal study. SETTING: University-based animal research facility. SUBJECTS: Sprague-Dawley male rats, weighing 200-250 g. INTERVENTIONS: Anesthetized rats were subjected to bilateral flank incisions, and the right kidney was removed. Renal ischemia was performed by left renal microvascular clamping, followed by reflow of the blood. MEASUREMENTS AND MAIN RESULTS: Ischemia of the kidney in the uninephrectomized rat significantly induced HO-1 messenger RNA, protein, and enzyme activity, reaching a maximum at 6 hrs, which was mediated in part through an increase in microsomal heme concentration. Heat shock protein 70 was induced extremely rapidly, reaching a maximum at 1 hr, suggesting that HO-1 and heat shock protein 70 gene expression are regulated separately. Inhibition of HO activity by tin mesoporphyrin, which resulted in an increase in microsomal heme concentration, significantly exacerbated renal function, as judged by the sustained increase in serum creatinine concentration and extensive tubular epithelial cell injuries. In contrast, animals that did not receive tin mesoporphyrin showed normal creatinine concentration and microsomal heme concentration 24 hrs after reperfusion, as well as restoration of abnormal renal histology. CONCLUSION: These findings indicate that the expression of HO-1 in the ischemic kidney may be critical in the recovery of renal cell function in this animal model. These findings also suggest that H0-1 induction may play an important role in conferring protection on renal cells from oxidative damage caused by heme.     

Osteogenic protein-1 (bone morphogenetic protein-7) reduces severity of injury after ischemic acute renal failure in rat.

We have shown that osteogenic protein-1 (OP-1) (bone morphogenetic protein-7) is responsible for the induction of nephrogenic mesenchyme during embryonic kidney development. Gene knock-out studies showed that OP-1 null mutant mice die of renal failure within the first day of postnatal life. In the present study, we evaluated the effect of recombinant human OP-1 for the treatment of acute renal failure after 60 min bilateral renal artery occlusion in rats. Bioavailability studies in normal rats indicate that approximately 1.4 microg OP-1/ml is available in the circulation 1 min after intravenous administration of 250 microg/kg, which then declines steadily with a half life of 30 min. About 0.5% of the administered OP-1 dose/g tissue is targeted for OP-1 receptors in the kidney. We show that OP-1 preserves kidney function, as determined by reduced blood urea nitrogen and serum creatinine, and increased survival rate when administered 10 min before or 1 or 16 h after ischemia, and then at 24-h intervals up to 72 h after reperfusion. Histochemical and molecular analyses demonstrate that OP-1: (a) minimizes infarction and cell necrosis, and decreases the number of plugged tubules; (b) suppresses inflammation by downregulating the expression of intercellular adhesive molecule, and prevents the accumulation and activity of neutrophils; (c) maintains the expression of the vascular smooth muscle cell phenotype in pericellular capillaries; and (d) reduces programmed cell death during the recovery. Collectively, these data suggest that OP-1 prevents the loss of kidney function associated with ischemic injury and may provide a basis for the treatment of acute renal failure.     

Peritoneal dialysis in acute renal failure.

Given the discussion so far, it might be apparent that factors beyond efficacy have dictated the decline in the use of PD for ARF. The importance of these factors should not be underestimated. They might be related to the perceived "labor intensive" aspect of PD, fear of a malfunctioning catheter (which in some instances may be real), insufficient exposure to PD during nephrology training, and, last, the comfort offered by the technology used for HD. Such psychological barriers are difficult to overcome, much more so than technical barriers (which can be and have been overcome). Only a concentrated effort by the PD community in educating the general nephrologist concerning the feasibility of PD in ARF, better clinical trials that harness the full potential of PD, and careful patient selection for the use of PD will bring PD back to the mainstream in the treatment of ARF.     

Free radical scavengers in mercuric chloride-induced acute renal failure in the rat

Oxygen free radicals have recently been found to mediate cell injury after ischemia in the kidney. We sought to determine whether oxygen free radicals mediate damage in mercuric chloride (HgCl2)-induced acute renal failure, a toxic model of acute renal failure. Neither superoxide dismutase nor allopurinol, which scavenges or inhibits production of superoxide radical, respectively, provided protection against renal dysfunction after HgCl2. Similarly, the hydroxyl radical scavengers tryptophan, N-acetyl-tryptophan, and ascorbic acid were unable to protect against HgCl2. However, dimethylthiourea and dimethyl sulfoxide, both hydroxyl radical scavengers, were beneficial. Dimethylthiourea completely prevented the rise in plasma creatinine concentration after HgCL2. In control rats plasma creatinine concentration rose from 0.4 mg/dl to 3.2 +/- 0.8, 5.1 +/- 1.0, and 6.1 +/- 1.6 mg/dl at 24, 48, and 72 hours after HgCl2. Dimethylthiourea-treated rats had plasma creatinine concentration less than 0.5 mg/dl at all times. Furthermore, a mixture of HgCl2 and equimolar amounts of dimethylthiourea was less toxic than HgCl2 alone. Dimethyl sulfoxide attenuated the HgCl2-induced rise in creatinine concentration: 1.3 +/- 0.2, 3.2 +/- 0.3, and 3.1 +/- 0.2 mg/dl at 24, 48, and 72 hours after HgCl2. Measurement of kidney malondialdehyde content after HgCl2 provided no evidence for oxygen free radical-mediated lipid peroxidation. We conclude that there is no convincing role for oxygen free radicals in the pathogenesis of HgCl2-induced acute renal failure. The ability of dimethylthiourea and dimethyl sulfoxide to protect against HgCl2-induced renal dysfunction may be related to their ability to form complexes with Hg2+.     

Properties of glomerular angiotensin receptors in acute renal failure in the rat

Angiotensin (AII) binds to specific glomerular receptors to modulate glomerular filtration rate (GFR) in the normal kidney. To test the hypothesis that altered AII binding to the glomerulus may contribute to the decreased GFR in acute renal failure (ARF) we studied the properties of glomerular AII receptors in models of ARF. ARF was induced in rats by either mercuric chloride (2.0 or 4.5 mg/kg) or 60 min renal ischemia. Outer cortical glomeruli isolated by sieving techniques were studied by equilibrium binding analysis. Scatchard analysis revealed one class of high-affinity receptors over a wide range of concentrations (10(-11)M to 10(-8)M). Angiotensin binding to specific glomerular receptors was studied at 2 and 24 hr after high-dose mercuric chloride. Glomerular AII receptor density was unchanged after mercuric chloride ARF [2 hr: 783 +/- 96 (N = 6), 24 hr: 765 +/- 69 (N = 4); normal control: 718 +/- 64 (N = 9)]. Likewise, the equilibrium affinity constant was unaltered after HgCl2 [2 hr: 1.85 +/- 0.28 X 10(8)M-1 (N = 6); 24 hr: 1.80 +/- 0.25 X 10(8)M-1 (N = 4); normal control: 2.02 +/- 0.21 X 10(8)M-1 N = 9)]. Plasma angiotensin II levels were elevated 2 hr after HgCl2 (normal 16.2 +/- 2.3 pg/ml; 2 hr 47.6 +/- 4.8) and returned to normal by 24 hr (17.2 +/- 2.4 pg/ml). Additional experiments performed 2 weeks after low-dose HgCl2-induced ARF and at 24 hr after unilateral renal artery clamp also demonstrated normal AII receptor affinity and density. These studies demonstrated that glomerular AII receptor binding is unaltered during the initiation, maintenance, and recovery phases of ARF. Changes in the binding characteristics of glomerular AII receptors do not play a role in the pathogenesis of ARF.