Ischemic acute renal failure

A nectar-feeding mammal avoids body fluid disturbances by varying renal function

To maintain water and electrolyte balance, nectar-feeding vertebrates oscillate between two extremes: avoiding overhydration when feeding and preventing dehydration during fasts. Several studies have examined how birds resolve this osmoregulatory dilemma, but no data are available for nectar-feeding mammals. In this article, we 1) estimated the ability of Pallas's long-tongued bats (Glossophaga soricina; Phyllostomidae) to dilute and concentrate urine and 2) examined how water intake affected the processes that these bats use to maintain water balance. Total urine osmolality in water- and salt-loaded bats ranged between 31 +/- 37 mosmol/kgH(2)O (n = 6) and 578 +/- 56 mosmol/kgH(2)O (n = 2), respectively. Fractional water absorption in the gastrointestinal tract was not affected by water intake rate. As a result, water flux, body water turnover, and renal water load all increased with increasing water intake. Despite these relationships, glomerular filtration rate (GFR) was not responsive to water loading. To eliminate excess water, Pallas's long-tongued bats increased water excretion rate by reducing fractional renal water reabsorption. We also found that rates of total evaporative water loss increased with increasing water intake. During their natural daytime fast, mean GFR in Pallas's long-tongued bats was 0.37 ml/h (n = 10). This is approximately 90% lower than the GFR we measured in fed bats. Our findings 1) suggest that Pallas's long-tongued bats do not have an exceptional urine-diluting or -concentrating ability and 2) demonstrate that the bats eliminate excess ingested water by reducing renal water reabsorption and limit urinary water loss during fasting periods by reducing GFR.

Hummingbirds arrest their kidneys at night: diel variation in glomerular filtration rate in Selasphorus platycercus

Small nectarivorous vertebrates face a quandary. When feeding, they must eliminate prodigious quantities of water; however, when they are not feeding, they are susceptible to dehydration. We examined the role of the kidney in the resolution of this osmoregulatory dilemma. Broad-tailed hummingbirds (Selasphorus platycercus) displayed diurnal variation in glomerular filtration rate (GFR). During the morning, midday and evening, GFRs were 0.9+/-0.6, 1.8+/-0.4 and 2.3+/-0.5 ml h(-1), respectively. At midday, GFR increased linearly with increased water intake. During the evening, hummingbirds decreased renal fractional water reabsorption linearly with increased water intake. Broad-tailed hummingbirds appeared to cease GFR at night (-0.1+/-0.2 ml h(-1)) and decreased GFR in response to short-term ( approximately 1.5 h) water deprivation. GFR seems to be very responsive to water deprivation in hummingbirds. Although hummingbirds and other nectarivorous birds can consume astounding amounts of water, a phylogenetically explicit allometric analysis revealed that their diurnal GFRs are not different from the expectation based on body mass.

Effect of antisense oligodeoxynucleotides for ICAM-1 on renal ischaemia-reperfusion injury in the anaesthetised rat

An antisense oligodeoxynucleotide (As-ODN) to the 3' untranslated region of the mRNA sequence expressing the intracellular adhesion molecule-1 (ICAM-1) was employed to determine ICAM-1's role in renal ischaemia-reperfusion injury in the rat. Wistar-Kyoto rats receiving i.v. either lipofectin-As-ODN (As-ODN group), lipofectin-reverse ODN (Rv-ODN group) or lipofectin (ischaemia control group) 8 h prior to study were anaesthetized and subjected to 30 min of renal artery occlusion. Renal haemodynamic and excretory parameters were monitored before and after renal ischaemia. On termination of the study renal tissue was subjected to histological and Western blot analysis. Renal blood flow decreased in the 3 h post-ischaemia period in the ischaemia control and Rv-ODN groups, but was maintained in the As-ODN group. Glomerular filtration rate was depressed initially but gradually increased to 10% above basal levels in the ischaemia control and Rv-ODN groups, but was below basal levels (20%) in the As-ODN group. There was a three- to fourfold increase in sodium and water excretion following ischaemia in the ischaemia control and reverse-ODN groups but not in the As-ODN treated group. The As-ODN ameliorated the histological evidence of ischaemic damage and reduced ICAM-1 protein levels to a greater extent in the medulla than cortex. These observations suggested that in the post-ischaemic period afferent and efferent arteriolar tone was increased with a loss of reabsorptive capacity which was in part due to ICAM-1. The possibility arises that the action of ICAM-1 at vascular and tubular sites in the deeper regions of the kidney contributes to the ischaemia-reperfusion injury.

Clinical and laboratory diagnosis of acute renal failure

Acute renal failure (ARF) is defined in general terms as an abrupt decrease in renal function sufficient enough to result in retention of nitrogenous waste and disrupt fluid and electrolyte homeostasis. There is no consensus regarding a quantifiable definition of ARF. Prompt evaluation of ARF is vital because ARF can be the end result of diverse processes which can often be reversed or attenuated through therapy directed at the underlying condition. Evaluation begins with careful review of the patient's history, previous medical records, physical examination, urinalysis, and available laboratory data. Routine urine chemical indices, calculation of the fractional excretion of sodium, and examination of the urine sediment are valuable in characterizing the cause of ARF. When this evaluation fails to yield a diagnosis, further testing may be required to evaluate intravascular volume status or diagnose a systemic disorder or glomerular cause of ARF. Response to therapeutic trials may provide a diagnosis. When a diagnosis cannot be made with reasonable certainty through this evaluation renal biopsy should be considered.

Role of atrophic tubules in development of interstitial fibrosis in microembolism-induced renal failure in rat

We explored the origin and participation of atrophic tubules in the progression of interstitial fibrosis using a new microembolic rat model of chronic renal failure in which foci of atrophic tubules with cuff-like basement membrane thickening developed at 4 weeks. Atrophic tubules, immunoreactive for vimentin and platelet-derived growth factor, were surrounded by transformed interstitial cells expressing platelet-derived growth factor receptor beta and alpha-smooth muscle actin. Some tubules in the deep cortex and the outer stripe of the outer medulla had a mosaic appearance. Tall, intact proximal tubular cells with a brush border and positivity for Phaseolus vulgaris erythroagglutinin, adjoined typical atrophic tubule cells having no brush border and an immunostaining pattern characteristic for atrophic tubules. The transformed interstitial cells expressing alpha-smooth muscle actin were located near atrophic but not intact tubular epithelial cells. Type IV collagen accumulated between damaged tubular cells and transformed interstitial cells. Heat shock protein 47 showed immunoreactivity in damaged epithelial cells and in interstitial myofibroblasts. Staining with an anti-endothelial antibody suggested damage to peritubular capillaries near atrophic tubules. By disturbance of microcirculation following microsphere injection, proximal tubular cells expressed vimentin and platelet-derived growth factor; diffusion of the latter presumably stimulated transformation of interstitial cells to myofibroblasts. Injured tubular epithelial cells and interstitial myofibroblasts both were responsible for interstitial fibrosis.

Effect of anticoagulation on renal function and protein excretion in experimental acute ischemic renal failure

Female Sprague-Dawley rats underwent right nephrectomy and 40 min left renal artery occlusion (RAO). After 15 min of reflow, polyethylene glycol 1000 (PEG1000) was infused to induce osmotic diuresis and to enable glomerular filtration rate (GFR) measurements. Urine was collected during a 90 min period, and the concentrations of PEG1000, albumin, IgG, IgM and fibrin(ogen)/degradation products (FIB) were assessed both in plasma and urine by radial immuno diffusion technique Groups of rats were subjected to saline + RAO, warfarin + RAO or sham-operation. GFR as measured by PEG1000 clearance averaged 0.61, 0.036 and 0.094 mL/min/100g BW/kidney in sham-operated, saline + RAO and warfarin + RAO rats, respectively. Urinary excretion of albumin and IgG increased substantially in both ischemic groups. IgM was not detected in any of the urine samples. FIB excretion was lowest in the saline + RAO group, possibly due to retention of FIB-containing obstructions in the tubules. Rats subjected to warfarin + RAO had significantly higher excretion of FIB. This result suggests that warfarin does not prevent the glomerular sieving of macromolecules in the glomerular filter, but reduces tubular obstruction by preventing fibrin formation, which may explain its positive effect on GFR.

Tissue-specific pattern of stress kinase activation in ischemic/reperfused heart and kidney

In this report we investigate the molecular mechanisms that contribute to tissue damage following ischemia and ischemia coupled with reperfusion (ischemia/reperfusion) in the rat heart and kidney. We observe the activation of three stress-inducible mitogen-activated protein (MAP) kinases in these tissues: p38 MAP kinase and the 46- and 55-kDa isoforms of Jun N-terminal kinase (JNK46 and JNK55). The heart and kidney show distinct time courses in the activation of p38 MAP kinase during ischemia but no activation of either JNK46 or JNK55. These two tissues also respond differently to ischemia/reperfusion. In the heart we observe activation of JNK55 and p38 MAP kinase, whereas in the kidney all three kinases are active. We also examined the expression pattern of two stress-responsive genes, c-Jun and ATF3. Our results indicate that in the heart both genes are induced by ischemia and ischemia/reperfusion. However, in the kidney c-Jun and ATF3 expression is induced only by ischemia/reperfusion. To correlate these molecular events with tissue damage we examined DNA laddering, a common marker of apoptosis. A significant increase in DNA laddering was evident in both heart and kidney following ischemia/reperfusion and correlated with the pattern of kinase activation, supporting a link between stress kinase activation and apoptotic cell death in these tissues.

Susceptibility of human proximal tubular cells to hypoxia: effect of hypoxic preconditioning and comparison to glomerular cells

In animals models, exposure of the brain, heart, or kidneys to sublethal ischemia induces tolerance for subsequent ischemia. However, the ability of human renal cells to undergo hypoxic preconditioning has not been evaluated. In addition, it is unclear if renal ischemic preconditioning induces resistance at the cellular level, or if preconditioning is a result of altered postischemic hemodynamics or the azotemic environment. In this study, we tested the ability of cultured human proximal tubular epithelial cells (PTEC) to undergo hypoxic preconditioning at the cellular level. Hypoxia was induced by incubating cells in an anaerobic incubator in glucose-free buffer (combined oxygen-glucose deprivation; COGD). Cell injury was assessed by lactate dehydrogenase (LDH) efflux, release of arachidonic acid metabolites, and light microscopy. PTEC preconditioned with 12 h of COGD and a 24-h recovery period had less LDH efflux than control PTEC after subsequent exposure to 20 h of COGD (15.0 +/- 2.5% vs. 44.0 +/- 3.4%, p < 0.05). Preconditioned PTEC also retained relatively normal morphology and had less release of arachidonic acid metabolites than control PTEC. Because renal ischemia is characterized predominately by tubular injury with relative sparing of the glomerulus, we determined if PTEC are more susceptible to hypoxic injury than glomerular cells. For further comparison, we also assessed the susceptibility to hypoxia of the porcine tubular epithelial cell line LLC-PK1. After exposure to 18 h of COGD, LDH efflux from PTEC (25.5 +/- 3.3%, mean +/- SEM) was lower than from LLC-PK1 cells (47.6 +/- 4.0%; p < 0.01), but not mesangial cells (22.7 +/- 5.0%) or glomerular endothelial cells (38.2 +/- 6.2%). In conclusion, we have demonstrated that cultured PTEC are as resistant to hypoxic injury as glomerular cells, and that PTEC attain cytoresistance after hypoxic preconditioning. Characterization of the molecular changes that occur in human PTEC after hypoxic preconditioning may reveal innate survival mechanisms that can be manipulated to promote protection from renal ischemia in patients.

Management of acute renal failure in the elderly. Treatment options

Renal changes that occur with aging mainly consist of impairment in the ability to concentrate urine and to conserve sodium and water. These physiological changes increase the risk of volume depletion and the prerenal type of acute renal failure (ARF) in elderly people. Bladder outlet obstruction caused by benign prostatic hypertrophy is a common cause of ARF in elderly men. Another frequent cause of ARF in the elderly is drug-induced nephropathy. Nonsteroidal anti-inflammatory drugs (NSAIDs) and antibiotics are most often implicated in the development of ARF in the elderly. However, considering the high usage of these drugs, the incidence of drug-induced nephropathy is relatively small. NSAIDs are more likely to cause ARF in patients with congestive heart failure, chronic renal disease (including diabetic nephropathy) or chronic liver disease than in otherwise healthy individuals. NSAID-induced ARF is often of the prerenal type, but may be caused by acute interstitial nephritis (AIN). The presence of heavy proteinuria or nephrotic syndrome differentiates NSAID-induced AIN from AIN caused by other drugs. Antibiotics, especially semisynthetic penicillins, more commonly give rise to AIN associated with peripheral blood eosinophilia and eosinophiluria than NSAIDs. Ciprofloxacin is increasingly reported to cause AIN. Fever commonly accompanies AIN, especially when induced by antibiotics. Aminoglycosides produce ARF by inducing acute tubular necrosis (ATN), which results from the excessive accumulation of myeloid bodies in the tubules. In all cases of ARF it is essential to obtain a good history, to perform a through physical examination, with particular attention to skin turgor, and to measure blood pressure, pulse rate (supine and upright), urinary electrolyte and creatinine levels. Fractional excretion of sodium and the urine:plasma creatinine ratio are reliable indices that distinguish prerenal ARF from ATN. A prompt response to fluid challenge, with an increase in urine output and urinary sodium excretion, and a rapid decrease in blood urea nitrogen, constitutes strong evidence for prerenal ARF. However, these indices are unreliable when prerenal ARF has progressed to ATN or when ARF has an obstructive pattern to begin with. In all cases of ARF, especially in elderly men, urinary tract obstruction should be suspected unless the history is otherwise clear cut. Ultrasound of the kidneys and bladder is a simple, non-invasive and meaningful test that can be used to rule out obstructive causes of ARF. If obstruction is the cause of ARF, ultrasound will be positive; in contrast, urinary obstruction is very unlikely if ultrasound findings are normal in a patient who has been oliguric or anuric for 48 hours or more. Similarly, acute glomerulonephritis, including rapidly progressive glomerulonephritis, should be suspected when ARF is associated with heavy proteinuria. In such instances, percutaneous renal biopsy is essential to document the diagnosis. It is of utmost importance to establish whether ARF is of prerenal or postrenal type, both of which are potentially fully reversible. In contrast, patients with ATN or rapidly progressive glomerulonephritis may not recover, or may only partially recover, their renal function. Haemodialysis and nutritional support are common measures for patients with severe ATN and a highly catabolic state. Corticosteroids and immunosuppressive therapy should be instituted for rapidly progressive glomerulonephritis, in addition to haemodialysis. haemodiafiltration instead of haemodialysis is recommended for patients who are haemodynamically unstable [i.e., with a persistently low blood pressure (systolic < or = 100 mm Hg)]. Haemodiafiltration has been shown to improve acid-base balance and uraemia better than standard haemodialysis. However, despite dialysis, mortality in patients with ARF associated with ischaemic ATN remains high.

Nitrendipine and superoxide dismutase in ischemic renal injury

The effect of the Ca entry blocker nitrendipine, the antioxidant superoxide dismutase (SOD), and a combination of nitrendipine and superoxide dismutase on postischemic renal function was studied in four groups (n = 24) of rats. The rats in group 1 (n = 6) were the ischemic control and received 10 mL of 0.9% NaCl. Group II (n = 6) received SOD 7.0 mg/kg. Group III (n = 6) received nitrendipine 1 mg/kg. Group IV (n = 6) received nitrendipine 1 mg/kg and SOD 7 mg/kg. After administration, both kidneys were rendered ischemic by cross-clamping the renal vessels for 60 min. Comparison of 24-h creatinine clearance (CCr) for 3 days after reversal of ischemia revealed: (a) nitrendipine alone was the most effective in preserving renal function (p < .05); (b) SOD provided some degree of improvement, but only on day 3 (p < .05); (c) a similar result was detected using a combination of nitrendipine and SOD (p < .05); (d) there was no significant difference between SOD and nitrendipine nor between SOD and the combination of nitrendipine/SOD; (e) there was a significant improvement with nitrendipine when compared to the combination of nitrendipine/SOD (p < .05).

Acute renal failure

Preview An abrupt decrease in the kidneys' ability to excrete waste products is a common cause of severe morbidity and death in critically ill patients. This complication may result from prerenal, renal parenchymal, or postrenal causes. The authors describe the clinical and laboratory evaluation of acute renal failure and offer an approach to prevention and appropriate management.

Improvement of therapeutic effect of human recombinant superoxide dismutase on ischemic acute renal failure in the rat via cationization and conjugation with polyethylene glycol

Therapeutic effect of superoxide dismutase (SOD) and three derivatives: a conjugate with polyethylene glycol (SOD-PEG2), a cationized derivative (cSOD), and a mannosylated derivative (Man-SOD), on acute renal failure induced by ischemia/reperfusion was studied in rats. SOD and derivatives were administered intravenously to the rat after nephrectomy of the right kidney and before and after 60 min occlusion of the left renal artery. At 48 hr after reperfusion, the renal function was evaluated by determining the urinary excretion rate of 14C-inulin injected intravenously. No therapeutic effect on the impaired renal function was shown in the case of low dose SOD (2600 unit/kg) treatment. In contrast, administration of cSOD which was shown to be taken up by the isolated perfused kidney from its capillary side and SOD-PEG2 which maintained high plasma concentration exhibited significant therapeutic effect, as did SOD at ten-fold higher dose (26,000 unit/kg). On the other hand, renal damage was promoted by Man-SOD. Thus, the present study demonstrated that chemical modification may improve the therapeutic effect of SOD on the ischemic acute renal failure and increased SOD concentration in the renal vascular space is an important factor for the improved effect.