Role of tubular obstruction in acute renal failure due to gentamicin

Mono-macrophage-Derived MANF Protects Against Lipopolysaccharide-Induced Acute Kidney Injury via Inhibiting Inflammation and Renal M1 Macrophages

The outburst of renal inflammatory response has been found to be a crucial cause of acute kidney injury (AKI). Attenuating the renal inflammation is an effective way for AKI treatment. Mesencephalic astrocyte-derived neurotrophic factor (MANF) has been proven to be an anti-inflammatory factor. However, the effect of MANF on renal inflammation induced by AKI is unknown. In this study, we have investigated the effect of mono-macrophage-derived MANF on AKI. We constructed the mono-macrophage-specific MANF knockout (Mø MANF^-/-) mouse and used lipopolysaccharide (LPS) to induce AKI in wild-type (WT) and Mø MANF^-/- mice. With mono-macrophage-specific MANF deficiency, Mø MANF^-/- mice had a lower survival rate, more severe renal injury, and higher serum level of pro-inflammatory TNF-α after AKI was induced by LPS. Also, compared with WT mice, there were more M1 macrophages in renal tissues of Mø MANF^-/- mice with LPS treatment, which might be attributed to the enhanced NF-κB activation in the renal microenvironment. Our study indicates the immunoregulatory role of mono-macrophage-derived MANF in the pathophysiological process of AKI, as well as the potential clinical application of MANF for AKI treatment.

Mechanisms of antimicrobial-induced nephrotoxicity in children

Drug-induced nephrotoxicity is responsible for 20% to 60% of cases of acute kidney injury in hospitalized patients and is associated with increased morbidity and mortality in both children and adults. Antimicrobials are one of the most common classes of medications prescribed globally and also among the most common causes of nephrotoxicity. A broad range of antimicrobial agents have been associated with nephrotoxicity, but the features of kidney injury vary based on the agent, its mechanism of injury and the site of toxicity within the kidney. Distinguishing nephrotoxicity caused by an antimicrobial agent from other potential inciting factors is important to facilitate both early recognition of drug toxicity and prompt cessation of an offending drug, as well as to avoid unnecessary discontinuation of an innocuous therapy. This review will detail the different types of antimicrobial-induced nephrotoxicity: acute tubular necrosis, acute interstitial nephritis and obstructive nephropathy. It will also describe the mechanism of injury caused by specific antimicrobial agents and classes (vancomycin, aminoglycosides, polymyxins, antivirals, amphotericin B), highlight the toxicodynamics of these drugs and provide guidance on administration or monitoring practices that can mitigate toxicity, when known. Particular attention will be paid to paediatric patients, when applicable, in whom nephrotoxin exposure is an often-underappreciated cause of kidney injury.

Effects of Proximal Tubule Shortening on Protein Excretion in a Lowe Syndrome Model

BACKGROUND

Lowe syndrome (LS) is an X-linked recessive disorder caused by mutations in OCRL, which encodes the enzyme OCRL. Symptoms of LS include proximal tubule (PT) dysfunction typically characterized by low molecular weight proteinuria, renal tubular acidosis (RTA), aminoaciduria, and hypercalciuria. How mutant OCRL causes these symptoms isn't clear.

METHODS

We examined the effect of deleting OCRL on endocytic traffic and cell division in newly created human PT CRISPR/Cas9 OCRL knockout cells, multiple PT cell lines treated with OCRL-targeting siRNA, and in orcl-mutant zebrafish.

RESULTS

OCRL-depleted human cells proliferated more slowly and about 10% of them were multinucleated compared with fewer than 2% of matched control cells. Heterologous expression of wild-type, but not phosphatase-deficient, OCRL prevented the accumulation of multinucleated cells after acute knockdown of OCRL but could not rescue the phenotype in stably edited knockout cell lines. Mathematic modeling confirmed that reduced PT length can account for the urinary excretion profile in LS. Both ocrl mutant zebrafish and zebrafish injected with ocrl morpholino showed truncated expression of megalin along the pronephric kidney, consistent with a shortened S1 segment.

CONCLUSIONS

Our data suggest a unifying model to explain how loss of OCRL results in tubular proteinuria as well as the other commonly observed renal manifestations of LS. We hypothesize that defective cell division during kidney development and/or repair compromises PT length and impairs kidney function in LS patients.

Nephroprotective effect of Rudgea viburnoides (Cham.) Benth leaves on gentamicin-induced nephrotoxicity in rats

RELEVANCE

Rudgea viburnoides, popularly known as "congonha-de-bugre" or "erva de bugre", is used in folk medicine as hypotensive, blood depurative, anti-rheumatic, diuretic and in the treatment of kidney and bladder pain.

AIM

Based on the popularly acclaimed nephron-protective effect of R. viburnoides, we investigated, using rats, the protective effect of this plant extract on gentamicin-induced kidney injury.

MATERIAL AND METHODS

Urinary volume, water and food intakes were assessed in adult male Wistar rats (naive or gentamicin-induced model of nephrotoxicity) treated with R. viburnoides extract. Also blood and kidney samples were collected for further laboratory and histological analyses.

RESULTS

R. viburnoides leaves extract improved renal function. It also improved the renal function impairments caused by gentamicin-induced nephrotoxicity, as revealed by glomerular filtration rate, urine output and proteinuria.

CONCLUSION

R. viburnoides exert renoprotective effect, which may support its popular use for renal diseases treatment.

Comparative effect of olive oil and fish oil supplementation in combating gentamicin induced nephrotoxicity in rats

The present study is related to the comparative effects of fish oil and olive oil supplementation on gentamicin induced nephrotoxicity in rats. Three treatment groups (Pretrement, Co-treatment and post treatment) were chosen for the study. Nephrotoxicity in rats was induced by intraperitonial administration of gentamicin (80 mg/kg/d) for 3,5,7,10,& 12 consecutive days. The animals were sacrificed 12 hrs after last treatment in each group. The maximum nephrotoxicity was developed on 10 days treatment of gentamicin. For each group a control group was taken without any oil or gentamicin treatment. Beneficial effects of oils were evidenced by reduced serum urea and creatinine concentrations in the group receiving oils compared to the non oil treatment animals receiving gentamicin only. Further, the changed values of alkaline phosphatase and acid phosphatase activity retumed to normal in kidney and liver tissue homogenates after fish and olive oil treatment. In this study, it was found that co-treatment of fish and olive oil is more effective antagonist of gentamicin induced nephrotoxicity. However fish oil was found to be more effective. Hypercholesteromia associated with gentamicin induced nephrotoxicity is also lowered by oil supplementations. The beneficial effects of these oils are due to counteracting effect of the biochemical alterations induced by the drug.

Accidental and iatrogenic causes of acute kidney injury

PURPOSE OF REVIEW

Ingestions and iatrogenic administration of drugs are all too common causes of acute kidney injury. This review will discuss these preventable causes of acute kidney injury.

RECENT FINDINGS

Recent studies have examined the pathophysiology of acute kidney injury by several commonly used drugs. These studies have shown that drugs and toxins can cause acute kidney injury by altering renal hemodynamics, direct tubular injury or causing renal tubular obstruction.

SUMMARY

Knowledge of the drugs that cause acute kidney injury and how this injury is manifested can lead to improved diagnosis and treatment with the ultimate goal of prevention.

New insights into the mechanism of aminoglycoside nephrotoxicity: an integrative point of view

Nephrotoxicity is one of the most important side effects and therapeutical limitations of aminoglycoside antibiotics, especially gentamicin. Despite rigorous patient monitoring, nephrotoxicity appears in 10-25% of therapeutic courses. Traditionally, aminoglycoside nephrotoxicity has been considered to result mainly from tubular damage. Both lethal and sub-lethal alterations in tubular cells handicap reabsorption and, in severe cases, may lead to a significant tubular obstruction. However, a reduced glomerular filtration is necessary to explain the symptoms of the disease. Reduced filtration is not solely the result of tubular obstruction and tubular malfunction, resulting in tubuloglomerular feedback activation; renal vasoconstriction and mesangial contraction are also crucial to fully explain aminoglycoside nephrotoxicity. This review critically presents an integrative view on the interactions of tubular, glomerular, and vascular effects of gentamicin, in the context of the most recent information available. Moreover, it discusses therapeutic perspectives for prevention of aminoglycoside nephrotoxicity derived from the pathophysiological knowledge.

Assessment of novel avian renal disease markers for the detection of experimental nephrotoxicosis in pigeons (Columba livia)

Renal disease is a major cause of illness in captive and wild avian species. Current renal disease markers (e.g., uric acid, blood urea nitrogen, and creatinine) are insensitive. Two endogenous markers, creatine and N-acetyl-beta-D-glucosaminidase (NAG), were selected for study in the pigeon (Columba livia). Representative organs from four pigeons were surveyed to determine those exhibiting the highest level of each marker. In a separate study, NAG and creatine from plasma and urine were assayed before and after gentamicin (50 mg/kg twice daily), administration for up to 9 days. Observer-blinded pathologic scoring (five saline solution controls, 17 treated birds) was used to verify the presence of renal disease that corresponded to marker increases. The first study revealed that kidney tissue had the highest NAG activity (by approximately six times), and pectoral muscle had the most creatine (>900 times). In response to gentamicin, plasma creatine (>five times) and NAG increased (approximately six times), which paralleled uric acid (>10 times). Urine creatine (approximately 60 times) and NAG increased dramatically (approximately 50 times) in response to gentamicin. In conclusion, NAG, especially in the urine, may be of value to noninvasively detect renal toxin exposures and to monitor potentially nephrotoxic drugs, and might be of value to screen free-ranging birds in large exhibits or in the wild by assaying fresh urate samples at feeding stations.

Protective effect of oral L-arginine administration on gentamicin-induced renal failure in rats

We investigated the effects of orally supplemented L-arginine, the substrate of nitric oxide (NO) and N(omega)-nitro-L-arginine methyl ester (L-NAME), a nitric oxide-synthase inhibitor in gentamicin-induced renal failure. Rats were given gentamicin (100 mg/kg/day s.c.), gentamicin and L-arginine (2 g/l, drinking water), gentamicin and L-NAME (100 mg/l, drinking water) or gentamicin plus L-arginine and L-NAME. After 8 days, the gentamicin group developed marked renal failure, characterized by a significantly decreased creatinine clearance and increased blood creatinine, fractional excretion of sodium, fractional excretion of lithium, urine gamma glutamyl transferase, systolic blood pressure and daily urine volume when compared to controls. Renal histological analysis confirmed tubular necrosis. L-arginine administration caused normalization of these parameters, whereas L-NAME led to aggravation of the failure. Concomitant administration of L-NAME and L-arginine to gentamicin-treated rats caused no significant changes when compared to the rats receiving gentamicin alone. We conclude that L-arginine supplementation has beneficial effects in gentamicin-induced renal failure in rats and that these effects are reversed by the NO-synthase inhibitor, L-NAME.

Nephrotoxicity of xenobiotics

Nephrotoxicity can be grouped by the xenobiotics place of action, by the clinical presentation or by the generic toxic effect. The latter can be dose related, indirect, idiosyncratic or allergic. Nephrotoxicity of lithium, demeclocycline, aminoglycosides, cyclosporine, mercuric ion, nonsteroidal anti-inflammatory drugs, methoxyflurane, ethylene glycol, D-penicillamine and methicillin is reviewed in light of all these three viewpoints, but emphasis is on toxic mechanisms.

Acute effects of gentamicin on thick ascending limb function in the rat

It is well established that the aminoglycoside antibiotics can adversely affect proximal tubule function. Predominantly indirect evidence suggests that aminoglycosides may also affect function of more distal nephron segments. The present study utilized whole kidney clearance, in vivo micropuncture and in vitro microperfusion to directly determine whether acute gentamicin treatment affects sodium chloride transport in the thick ascending limb of the loop of Henle. Gentamicin (25 mg/kg) significantly increased urine flow, as well as sodium, potassium and chloride excretion within 15 min of intravenous injection. Glomerular filtration rate and proximal tubule fluid reabsorption were not altered by acute gentamicin treatment. In contrast, both fractional and absolute loop chloride transport was significantly decreased. In the in vitro microperfused medullary thick ascending limb, luminal but not basolateral administration of gentamicin (1 mM) significantly decreased chloride reabsorption when compared to time controls. These data suggest that the increased urine and electrolyte excretion associated with acute gentamicin treatment is, at least in part, a consequence of decreased transport in the thick ascending limb of Henle's loop.

Roles of hemodynamic and tubular factors in gentamicin-mediated nephropathy

Gentamicin (GM) often causes polyuric acute renal failure (ARF) in humans and animals. GM-mediated ARF in rats was accompanied with activated renin-angiotensin system, increased renal endothelin content, and enhanced lipid peroxidation. Suppression of the renin-angiotensin activity by desoxycorticosterone acetate and saline drinking, and treatment with superoxide dismutase attenuated the GM-induced decline in whole-kidney GFR with well-maintained RBF but did not reduce the severity of tubular necrosis. On the other hand, treatment with dimethylthiourea, a hydroxyl radical scavenger, attenuated the GM-mediated decline in GFR and lessened tubular necrosis but did not ameliorate the reduction in RBF. These data suggest contributions of both vascular and tubular factors to the GM-induced decline in GFR in rats. However, relative importance of these factors probably differs with different doses of the agent.

Effects of desoxycorticosterone acetate (DOCA) plus saline drinking on gentamicin-mediated nephropathy in rats

Studies were performed to examine the effect of desoxycorticosterone acetate (DOCA) treatment plus isotonic saline drinking on gentamicin (GM)-mediated nephropathy in rats. GM, 40 mg/kg/day, was subcutaneously injected for 13 days following a 5-week treatment with water drinking or DOCA (10 mg/kg/week) plus saline drinking. Twenty-four hours after the last injection of GM, renal blood flow (RBF) and Cin decreased to approximately 69% and 52% of the control values in water-drinking GM-treated rats, respectively, but was well maintained in DOCA plus saline-drinking GM-treated animals. There was no significant difference in morphologic tubular injury or the renal cortical GM content between GM-treated groups. Saline drinking alone (1% saline, 5 weeks) lessened neither GM-induced reduction in GFR nor tubular damage. Body weight loss occurred following GM injection in the water-drinking group but not in the DOCA plus saline-drinking and saline-drinking-alone groups. DOCA plus saline drinking significantly suppressed the plasma renin activity (PRA) but saline drinking alone did not. A significant inverse correlation was found between PRA and Cin in water-drinking GM-treated and untreated rats. The data suggest that the beneficial effect of DOCA plus saline drinking is associated with renin-angiotensin suppression rather than with the renal GM content or well-maintained hydration.

Effect of indomethacin on glomerular permselectivity and hemodynamics in nephrotoxic serum nephritis

The present study was undertaken to determine the effects of prostaglandin synthesis inhibition on glomerular hemodynamics in nephrotoxic serum nephritis and to elucidate the mechanisms by which prostaglandin synthesis inhibition reduces proteinuria in nephritic rats. Dextran sieving studies were performed before and after intravenous administration of indomethacin to control rats and to nephritic rats with heavy proteinuria. Indomethacin did not significantly alter mean arterial pressure, glomerular filtration rate or proteinuria in control rats nor were significant changes in dextran sieving observed. By contrast, in nephritic rats indomethacin significantly reduced glomerular filtration rate (2.58 +/- 0.50 vs. 1.39 +/- 0.27 ml/min, P less than 0.001), proteinuria (0.198 +/- 0.079 vs. 0.048 +/- 0.019 mg/min, P less than 0.05) and filtration rate-corrected proteinuria (0.059 +/- 0.033 vs. 0.031 +/- 0.013 mg/ml GFR, P less than 0.05). The fractional clearance of neutral dextrans with molecular radii exceeding 42 A were elevated above control values in nephritic rats (P less than 0.05). After administration of indomethacin, the fractional clearance of neutral dextrans uniformly declined toward control values and remained elevated only for molecular radii exceeding 54 A. Assessment of glomerular hemodynamics in nephritic rats before and after indomethacin showed significant declines in single nephron filtration rate (31.5 +/- 3.0 vs. 21.2 +/- 2.5 nl/min, P less than 0.02), glomerular plasma flow rate (99.5 +/- 6.7 vs. 68.5 +/- 7.8 nl/min, P less than 0.05) and glomerular ultrafiltration coefficient (0.0430 +/- 0.0033 vs. 0.0339 +/- 0.0032 nl.sec-1.mm Hg-1, p less than 0.05). Indomethacin did not significantly change these parameters in control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of aminoglycoside nephrotoxicity

Aminoglycosides continue to be widely used for the treatment of serious Gram-negative infections. Ten to fifteen per cent of all courses of therapy are complicated by declines in renal function, despite close monitoring of serum drug levels. The proposed pathogenesis and biochemical mechanisms of renal dysfunction caused by these commonly used therapeutic agents are discussed.

Glomerular size-selective barrier dysfunction in nephrotoxic serum nephritis

We have previously reported amelioration of heavy proteinuria, vascular sclerosis and glomerular structural damage by antihypertensive therapy in nephrotoxic serum nephritis (NSN). In the present study, we examine glomerular permselectivity in this hypertensive form of NSN and the effect of hypertension treatment on size-selective barrier function. Mean arterial pressure was maintained at normotensive levels (mean 123 +/- 3 mm Hg) with a combination of hydralazine, hydrochlorthiazide and reserpine in 7 nephritic rats, while 10 untreated rats remained hypertensive (mean 165 +/- 4 mm Hg). At six weeks, glomerular filtration rate was reduced in untreated rats (mean 0.54 ml/min) but was preserved in those rendered normotensive (mean 1.71 ml/min), P less than 0.02). Twenty-four-hour urinary protein excretion, mean 371 +/- 74 mg in hypertensive nephritic rats, was markedly reduced in rats on the antihypertensive regimen to a mean of 120 +/- 17 mg (P less than 0.02), as was 24-hour urinary gamma-globulin excretion (mean 35 +/- 9 mg in untreated vs. 16 +/- 2 mg in treated). Fractional clearances of tritiated polydisperse neutral dextrans were significantly enhanced for molecular radii exceeding 50 angstroms in hypertensive animals, indicative of a loss of glomerular size permselectivity. Rats on antihypertensive therapy did not develop such a size selective defect. Thus, hypertensive rats with nephrotoxic serum nephritis develop "gaps" in the glomerular basement membrane which allow the excretion of large molecular weight neutral dextrans and gamma-globulin. This defect in glomerular permselectivity can be averted with antihypertensive therapy.

Effects of dietary electrolyte supplementation on gentamicin nephrotoxicity

The effects of electrolyte supplementation via drinking solutions on gentamicin-induced nephrotoxicity were studied in rats. Four groups of animals were injected with gentamicin, 120 mg/kg daily for 5 days and were studied 2-4 days after the last injection. Electrolyte supplements were begun before the gentamicin injections and were continued throughout the study. The drinking solutions were tap water, NaCl, NaCl + KCl, or NaHCO3 + KHCO3 + diamox. At the end of the study, blood urea nitrogen (BUN) and serum creatinine were markedly increased only in the group receiving tap water. Nevertheless, 24 hour creatinine clearance in awake rats and inulin clearance in anesthetized rats were found to be severely reduced in all gentamicin-treated animals. However, the rats receiving NaHCO3 + KHCO3 + diamox had significantly higher creatinine clearance than all other experimental groups. Proximal intratubular free-flow pressure, measured by micropuncture, and internal proximal diameters were significantly increased above normal controls in all groups, but were least abnormal in the rats receiving HCO3- and diamox. Semiquantitative histologic evaluation revealed significantly less tubular necrosis and cast formation in this group than in all the other experimental groups. The observations suggest that dietary sodium, potassium, and chloride supplements, even accompanied by large fluid intake, provide relatively little protection against gentamicin nephrotoxicity. In contrast, HCO3- and diamox supplements resulted in significant, albeit incomplete, protection of GFR and renal histology.

Nephrotoxic serum nephritis with hypertension: perfusion pressure and permselectivity

We examined the effect of acute reduction in renal perfusion pressure on proteinuria and glomerular permselectivity in a model of nephrotoxic serum nephritis which is characterized by hypertension, heavy proteinuria and severe structural injury. Sequential dextran sieving studies were performed after two weeks of nephritis in 10 uninephrectomized rats at their basal elevated blood pressure levels (154 +/- 3 mm Hg) and at lowered renal perfusion pressure of 105 to 110 mm Hg, achieved by adjusting a ligature around the aorta above the origin of the renal artery. Glomerular filtration rate (GFR) decreased from 1.35 +/- 0.24 to 0.95 +/- 0.19 ml/min (P less than 0.002), while urinary protein excretion (factored for filtration rate) declined from 0.69 +/- 0.2 to 0.39 +/- 0.1 mg per ml GFR (P less than 0.002) at the lower perfusion pressure. A companion protocol documented a modest reduction in renal plasma flow (RPF) from 4.96 +/- 0.48 to 4.44 +/- 0.63 ml/min (P less than 0.05) and a decline in glomerular transcapillary hydraulic pressure difference (delta P) from 43 to 33 mm Hg (P less than 0.001) during the ligature maneuver. In the hypertensive state, fractional clearances of neutral dextrans (theta ND) with molecular radii exceeding 40 A were elevated in nephritic rats as compared to uninephrectomized non-nephritic controls. With reduction in renal perfusion pressure. Theta ND uniformly declined toward control values and remained significantly elevated only for molecular radii exceeding 55 A. The calculated fraction of glomerular filtrate passing through a non-size discriminatory shunt, pathway was 0.93% during the hypertensive period and was reduced at lower perfusion pressures to 0.52% (to be compared to 0.19% in controls).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of cyclosporin A, gentamicin and furosemide on rat renal function: a lithium clearance study

1. This study applied clearance methods of inulin, lithium, potassium, sodium and para-aminohippuric acid (PAH) for investigation of the effects of cyclosporin A (CyA), furosemide and gentamicin on rat (n = 92) renal function. The drugs were dosed for 2 weeks; CyA 12.5 mg/kg per day, gentamicin 32 mg/kg per day and furosemide 5 mg/kg per day. 2. The questions asked were: could these methods differentiate the effects of drugs with different sites of action, and would gentamicin or furosemide exaggerate the nephrotoxicity of CyA? 3. Furosemide increased sodium clearance (CNa) 74% and fractional sodium clearance (FENa) 105%, while fractional sodium reabsorption in the distal nephron (FDNR) was reduced, compared with placebo-treated controls. 4. Gentamicin reduced CPAH 29% and Cin 37%, while FENa increased 335%. Proximal fractional reabsorption (PFR) and absolute proximal reabsorption (APR) decreased. 5. CyA depressed CPAH 32% and lithium clearance (CLi) 56%, and increased PFR. 6. The effects of CyA and furosemide in reducing renal function were not additive. 7. CyA plus gentamicin reduced CPAH to 35% of the value in untreated controls, equal to 52% of the CPAH of CyA-treated rats; Cin was reduced to 46% of the Cin of CyA-treated rats. 8. Rats given CyA, furosemide and gentamicin had decreased Cin, CPAH and CLi compared with rats given either CyA plus furosemide or gentamicin plus furosemide. 9. Thus, in this investigation of drugs known to have different sites of actions, the differences in renal and tubular function were discernible with the lithium clearance method. 10. The nephrotoxicities of CyA and of gentamicin were additive, while furosemide did not aggravate CyA nephrotoxicity.

Evidence against increased glomerular pressure initiating diabetic nephropathy

Studies were carried out to determine whether exaggerated glomerular hydraulic pressure (PG) initiates the development of glomerular pathology and proteinuria in insulin-dependent diabetic rats. Normotensive (WKY) and hypertensive rats (SHR) were made diabetic by streptozotocin injection. One group of SHR diabetic rats was treated with antihypertensive drugs to reduce blood pressure. One week after onset of diabetes, micropuncture determinations of PG, measured by stopped-flow technique, revealed that PG was higher in WKY diabetics than in non-diabetic WKY controls, and that PG was even higher in SHR diabetics (P less than 0.05). Similarly prepared groups of animals were followed for six months, approximately one fifth to one third of the expected life span of these rats. Tail systolic blood-pressure measurements documented continuous severe systolic-hypertension in SHR diabetics, normal pressure in the WKY diabetics and hypotension in the SHR diabetics treated continuously with antihypertensive drugs. Urinary protein excretion, measured monthly, was statistically the same in all groups, with no evidence of a progressive rise in the SHR diabetics. PG measured in two rats from each group after four months of diabetes was similar to values found after one week of diabetes. Semiquantitative histologic scoring of glomerular mesangial expansion after six months of diabetes failed to demonstrate any significant difference between the normotensive WKY diabetics and the hypertensive SHR diabetics. These observations suggest that elevated PG does not in itself initiate glomerular pathology or proteinuria in diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)

Proton MR study of different types of experimental acute renal failure in rats

Kidney cortical and medullary spin-lattice (T1) and spin-spin (T2) relaxation times were measured in several types of experimental acute renal failure in rats with a Bruker PC "Multispec." Gentamicin ARF was obtained after one i.p. injection of 100mg Gentamicin/kg BW/day for 8 days. Glycerol ARF: 24 hours after one i.m. injection of 10 ml 50% Glycerol/kg BW. Obstruction ARF: 3 days after complete ureteral ligation. Renal tissue total water content, hydration fraction, fraction bound, blood urea and creatinine were measured at the end of the experiments. Shortened T1 and prolonged T2 were found in both cortex and medulla in the Glycerol ARF group. Gentamicin renal toxicity and the non-functioning kidney with ureteral obstruction are characterized by significant prolongation of T1 and T2 in cortex, while the medullary T1 and T2 were prolonged only in obstruction ARF. The highest T1 and T2 were found in the obstructed non-functioning kidney. The total water content decreased in the Glycerol ARF, increased in the obstruction and remain unchanged in Gentamicin ARF. The hydration fraction and the fraction bound changed significantly in the opposite direction with the total water content. Different profiles of renal cortical and medullary magnetic resonance properties found in several models of experimental ARF in rats indicate that MR properties may provide etiopathogenetic diagnostic possibilities.

Nephrotoxic tubular and interstitial lesions: morphology and classification

Nephrotoxic renal injury, and especially drug nephrotoxicity is now a common cause of acute renal failure. The most common patterns of renal injury produced by nephrotoxins, tubular damage, and interstitial nephritis, are discussed here. Toxic agents which are primarily tubular toxins include certain antibiotics, cisplatinum, anesthetics, and radiocontrast agents. In tubules injured by toxins, alterations range from subtle ultrastructural abnormalities to extensive tubular necrosis. Mechanisms of tubular injury include direct tubular cell toxicity, and alterations in intrarenal blood flow producing secondary tubular damage. Other commonly used therapeutic agents, including the penicillins, other antibiotics, and non-steroidal anti-inflammatory agents, produce renal dysfunction by inducing interstitial nephritis. Long-term analgesic abuse is associated with a particularly striking interstitial damage with frank papillary necrosis. Criteria for differentiating primary tubular injury with inflammation and primary interstitial nephritis with tubular injury are discussed. Individual commonly-used therapeutic agents are considered in some detail, with discussion of both clinical and morphological aspects of drug nephrotoxicity.

Nephrotoxic serum nephritis with hypertension: amelioration by antihypertensive therapy

We have examined the effects of antihypertensive therapy on glomerular dynamics and on the clinical and morphologic features of a model of nephrotoxic serum nephritis (NSN) in which hypertension occurs. NSN was induced in uninephrectomized male Sprague Dawley rats, which drank 0.9% sodium chloride ad libitum. One-half were assigned randomly to a treated group whose blood pressure was normalized on a regimen of reserpine, hydralazine, and hydrochlorothiazide. Hypertension continued throughout the 6 weeks of study in untreated rats (blood pressure 148 +/- 5 vs. 103 +/- 3 mm Hg in treated rats, P less than 0.01). Urinary protein excretion was greater (437 +/- 110 vs. 254 +/- 81 mg/24 hr, P less than 0.005), and serum albumin lower (1.6 +/- 0.4 vs. 2.9 +/- 0.3 g/dl, P less than 0.01) in hypertensive animals. Diffuse glomerular endo- and extracapillary proliferation and arteriolar medial hypertrophy were observed frequently in nephritic rats with untreated hypertension. By contrast, structural abnormalities were limited primarily to focal segmental proliferation involving fewer than one-third of glomeruli in the absence of vascular changes in treated normotensive rats. Micropuncture studies performed 8 to 16 days after induction of nephritis showed a reduction in glomerular capillary pressure (46 +/- 1 vs. 55 +/- 1 mm Hg, P less than 0.001), glomerular plasma flow rate (115 +/- 20 vs. 160 +/- 20 nl/min, P less than 0.01), and single nephron filtration rate (42 +/- 4 vs. 56 +/- 5 nl/min, P less than 0.001) with antihypertensive treatment, suggesting that a hemodynamic mechanism may have been responsible for enhanced glomerular injury in the hypertensive nephritic animals.

Mechanisms of lysine-induced acute renal failure in rats

We have previously found that lysine produces acute renal failure in rats. To define the acute effects of lysine, rats given lysine at 8.9 mg/kg/min, i.v. for 4.5 hr were compared with control rats receiving equiosmolar dextrose. Systemic blood pressure was stable in both groups. Mean intratubular pressure, inulin clearance (CIn), and renal blood flow were determined at 45-min intervals. Intratubular pressures measured with a servonulling micropressure device were elevated by 90 min in lysine-treated animals, with tubular heterogeneity, while pressures in dextrose-treated rats were normal and homogeneous. By 135 min CIn in lysine-treated rats was 45% of CIn in dextrose rats. Urine output fell in lysine-treated rats. Renal blood flow determined by flow probe remained normal in lysine-treated rats through 135 min and did not decline significantly until 180 min. Significant dilatation of surface tubules was documented by intravital microscopy beginning at 90 min in lysine-treated rats. The sequence of elevated intratubular pressure and tubular dilatation, followed by decreased CIn, and then by decreased renal blood flow suggests that lysine produces acute renal failure primarily through tubular obstruction. The tubular obstruction is followed later by an increase in renal vascular resistance.

Nephron heterogeneity in ischemic acute renal failure

To uncover the reasons for reported internephron heterogeneity in acute renal failure (ARF) serial micropuncture experiments in norepinephrine-induced ARF and sham-infused control rats were carried out to investigate this phenomenon. Proximal tubular pressures (PT) were scattered at 24, 48, and 72 hr in ARF rats ranging from 4 to 42 mm Hg, but the majority were greater than the mean control values (10 +/- 1 mm Hg). One week ARF PT were less variable than on previous days (5 to 17 mm Hg). The decreased variability was the result of a reduced number of PT values that were greater than controls. When single nephron filtration rates (SNGFR) were measured with spontaneous flow collections without maintaining the existent tubular pressures, results were widely scattered on each day. When SNGFR were measured at the existent PT, individual determinations were tightly clustered on each experimental day, clearly different from controls (all P less than 0.001), and correlated closely with predicted values from whole kidney inulin clearance (all P less than 0.001). Thus, existent internephron SNGFR was uniform in ARF rats and apparent heterogeneity, in large part, was attributable to an artifact of the tubular fluid collection technique. Despite the uniformity of SNGFR, values of PT ranging below as well as above controls, suggested that a mechanism in addition to tubular obstruction was operative in reducing SNGFR. Recoveries of microperfused 14C-inulin were similar to controls excluding significant backleak of tubular fluid.(ABSTRACT TRUNCATED AT 250 WORDS)