Renal hemodynamics in uranyl acetate-induced acute renal failure of rabbits

Renal interstitial fibrosis (RIF): II. Ultrasound follow up study of single uranyl nitrate administration causing renal dysfunction in rats--comparison with histologic and functional renal parameters

A single administration of uranyl nitrate (UN; 0.5 mg/100 g b. wt. i.p.) to adult female Wistar rats reliably induces renal interstitial fibrosis (RIF) providing an experimental model to investigate therapeutic strategies. It was the aim of this study to further characterise a rat model of UN induced RIF which we have studied previously (Appenroth et al. 2001) by the comparison of functional parameters with ultrasonographic examination over a period of 30 weeks after injury. In the acute phase after UN administration (between days 2 and 17) signs of inflammation (increase in renal blood flow, swelling of renal cortex, enlargement of renal pelvis) could be detected by ultrasound. After four weeks UN led to functional changes (decreased creatinine clearance, increased urinary protein excretion and increased OH-proline concentration in renal tissue). In vitro, the accumulation of p-aminohippurate and the gluconeogenesis were reduced. In accordance with the functional changes, distinct ultrasonographic abnormalities could be seen between weeks 10 and 30 after UN with regard to changes in kidney size and shape, reduced renal perfusion and enlargement of renal pelvis. The sensitivity of ultrasonography in small laboratory animals is limited and most useful for follow-up studies of acute renal changes after administration of nephrotoxins. Ultrasonography can not be recommended for non-invasive screening of the progression of chronic renal failure.

Understanding renal toxicity of heavy metals

The mechanisms by which metals induce renal injury are, in general, poorly understood. Characteristic features of metal nephrotoxicity are lesions that tend to predominate in specific regions of the nephron within specific cell types. This suggests that certain regions of the nephron are selectively sensitive to specific metals. Regional variability in sensitivity could result from the localization of molecular targets in certain cell populations and/or the localization of transport and binding ligands that deliver metals to targets within the nephron. Significant progress has been made in identifying various extracellular, membrane, and intracellular ligands that are important in the expression of the nephrotoxicity of metals. As an example, mercuric chloride induces a nephropathy that, at the lowest effective doses, is restricted primarily to the S3 segment of the proximal tubule, with involvement of the S2 and S1 segments at higher doses. This specificity appears to be derived, at least in part, from the distribution of enzymes and transport proteins important for the uptake of mercury into proximal tubule cells: apical gamma-glutamyltranspeptidase and the basolateral organic anion transport system. Regional distributions of transport mechanisms for binding proteins appear to be important in the expression of nephrotoxicity of metals. These and other new research developments are reviewed.

Pathological and biochemical modifications of renal function in ibuprofen-induced interstitial nephritis

Use of ibuprofen in patients with asymptomatic renal failure is known to produce acute renal toxicity. One of the manifestations is interstitial nephritis of which the pathogenic mechanism remains unclear. In the present study, this nephrotoxic syndrome was induced in rabbits by giving a single dose of uranyl nitrate, followed by consecutive doses of ibuprofen. This animal model thus allowed the assessment of renal functional and pathological changes associated with ibuprofen use in renal insufficiency. In these rabbits, the major abnormality appeared to be confined to the tubulointerstitial compartment. Microscopic examinations of the renal necropsy specimens showed tubular necrosis and interstitial lymphocytic infiltration. The histological finding of lymphocytic aggregation suggests that this nephrotoxic effect stems from a cytotoxic immune reaction in the interstitium. Moreover, levels of renal 2-arylpropionyl-CoA epimerase, a key enzyme involved in the metabolic inversion of ibuprofen, showed a significant reduction, which may result from the massive destruction of the tubular cells in these animals. These results support the premise that renal insufficiency is a prerequisite factor for ibuprofen-induced interstitial nephritis.

Effects of oxygen free radical scavengers on uranium-induced acute renal failure in rats

Study was made to determine whether oxygen free radicals mediate uranium-induced acute renal failure (ARF). Superoxide dismutase (SOD), a superoxide anion scavenger, did not prevent uranium acetate (UA) (5 mg/kg, i.v.)-induced renal injury 48 h after injection. In contrast, dimethylthiourea (DMTU), a hydroxyl radical scavenger, significantly attenuated UA-induced rise in serum creatinine concentration (1.11 +/- 0.05 (DMTU) vs. 1.40 +/- 0.06 mg/dl (control), p < .05), and tubular necrosis. Dimethyl sulfoxide (DMSO), a hydroxyl radical scavenger, decreased UA-induced tubular damage. UA injection caused no increase in renal cortical malondialdehyde (MDA) content. DMTU and DMSO did not modify intrarenal MDA content. UA administration brought about significant increase in plasma renin activity but not in renal cortical renin content. Treatment with DMTU and DMSO had no effect on plasma renin activity or intrarenal renin content. It follows from these findings that DMTU and DMSO may attenuate UA-induced renal injury. Such a protective effect would not be mediated through modulation of lipid peroxidation or renin activity.

Glomerular alterations in experimental oliguric and nonoliguric acute renal failure

Studies were performed in oliguric and nonoliguric forms of uranyl acetate (UA)-induced and ischemic acute renal failure (ARF) to examine whether a reduction in GFR is correlated with glomerular morphologic alterations. UA-induced nonoliguric and oliguric ARF were induced in rabbits by i.v. injections of 0.9 and 2 mg/kg, respectively. A 60-min renal artery clamping produced nonoliguric ARF in previously uninephrectomized rats, but oliguric ARF in the clamped kidneys of sham-nephrectomized animals. A decline in the whole-kidney CIn rate was more marked in oliguric ARF kidneys of both models than in nonoliguric ARF kidneys. Also, tubular damage was more pronounced in oliguric kidneys when compared with nonoliguric kidneys. Scanning electron microscopic observations revealed glomerular alterations in oliguric and nonoliguric kidneys in both models, evidenced by a flattening and spreading of podocyte cell bodies associated with loss of epithelial foot processes and a reduction in the density and diameter of endothelial fenestrae. There was no significant difference in these glomerular changes between oliguric and nonoliguric kidneys. The findings suggest that less reduction in the whole-kidney GFR in nonoliguric ARF kidneys is ascribed largely to less pronounced tubular damage rather than to less severe glomerular morphologic alterations.

Early effects of uranyl nitrate on respiration and K+ transport in rabbit proximal tubule

The mechanisms by which uranyl nitrate (UN) is toxic to the proximal tubule are incompletely understood. To define these further we studied potassium (K+) transport and oxygen consumption (QO2) in rabbit proximal tubule suspensions in vitro immediately after exposure to UN using extracellular O2- and K+-sensitive electrodes. UN caused a cumulative dose-dependent inhibition of proximal tubule QO2, with a threshold concentration of 5 x 10(-5) M. Kinetic analysis suggested two patterns of cell injury: a higher affinity inhibition of QO2 with a Ki of 5 x 10(-4) M, and a lower affinity inhibition of QO2 with a Ki of 10 mM. QO2 was studied in detail in the presence of these Ki concentrations of UN to define the initial cellular events. The results indicated that different cellular processes displayed different sensitivities to UN. At submillimolar concentrations UN caused progressive selective inhibition of ouabain-insensitive QO2 (15% inhibition at 2 minutes). Ouabain-sensitive QO2 and nystatin-stimulated QO2 were not affected, suggesting that Na+,K+-ATPase activity and its coupling to mitochondrial ATP synthesis were intact. Direct measurement of proximal tubule net K+ flux confirmed that Na+,K+-ATPase activity was unchanged. Similarly, UN did not inhibit basal (state 4) or ADP-stimulated (state 3) mitochondrial QO2 in digitonin-permeabilized tubules, confirming that the mitochondria were intact. In contrast, higher concentrations of UN (greater than or equal to 1 mM) caused rapid inhibition of QO2 and net K+ efflux, due to inhibition of Na+,K+-ATPase activity and mitochondrial injury.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of glomerular responses to vasoconstrictor agents in rabbits recovering from ARF

Glomerular responses to angiotensin II (AII), arginine vasopressin (AVP), and norepinephrine (NE) were estimated in rabbits recovering from uranium-mediated nephropathy or ischemic acute renal failure (ARF) to examine roles of intraglomerular events in resistance to ARF. Uranyl acetate (UA, 0.8 mg/kg) produced ARF in some animals but did not in others. Rabbits recovering from UA-induced ARF were highly resistant to a rechallenge with a larger dose of the agent (2 mg/kg). Their glomeruli did not respond to AII, AVP and NE in vitro. In animals having not experienced ARF following the initial insult, however, resistance to the rechallenge was lower than in animals recovering from ARF, and the glomerular response to contractile stimuli was well sustained. A two hour clamping of the renal artery induced ARF in uninephrectomized rabbits. These animals were not resistant to an additional ischemia in the recovery phase, despite inhibited glomerular contractile responses to AII. These data indicate a nonspecific inhibition of glomerular responses to contractile stimuli in the recovery phase of ARF. It is unlikely, however, that resistance to ARF can be attributed to the loss of the glomerular contractile response.

Glomerular alterations in uranyl acetate-induced acute renal failure in rabbits

The study was performed to elucidate the progression and regression of superficial and inner glomerular alterations in uranyl acetate-induced renal failure in rabbits. Fifteen hours after the drug injection, creatinine clearance (CCr) decreased to 55% of controls with slightly elevated plasma creatinine concentration (initiation stage). After 5 days, urine flow and CCr decreased to approximately zero, with severe azotemia (maintenance stage). Scanning electron microscopic observations in these stages revealed a flattening and spreading of podocyte cell bodies associated with loss of epithelial foot processes, and reduction in the density of endothelial fenestrae. These changes were more advanced in the maintenance stage. Glomerular and fenestral diameters did not significantly change in the initiation stage but increased in the maintenance stage. There was no significant difference in these morphologic alterations, however, between the superficial and inner glomeruli. Glomerular alterations reverted to normal within 14 days, with good recovery of glomerular function. The findings show no significant difference in the progression or regression of the glomerular changes between the superficial and deep cortex. These morphologic changes may play a role in the reduction of CCr observed in this model.

Mechanism of increased renal prostaglandin E2 in uranyl nitrate-induced acute renal failure

We have previously demonstrated that decreased cortical prostaglandin metabolism can contribute significantly to an increase in renal tissue levels and activity of prostaglandin E2 in bilateral ureteral obstruction, a model of acute renal failure. In the present study, we have further investigated whether alterations in prostaglandin metabolism can occur in a nephrotoxic model of acute renal failure. Prostaglandin synthesis, prostaglandin E2 metabolism (measured as both prostaglandin E2-9-ketoreductase and prostaglandin E2-15-hydroxydehydrogenase activity), and tissue concentration of prostaglandin E2 were determined in rabbit kidneys following an intravenous administration of uranyl nitrate (5 mg/kg). No changes in the rates of cortical microsomal prostaglandin E2 and prostaglandin F2 alpha synthesis were noted at the end of 1 and 3 days, while medullary synthesis of prostaglandin E2 fell by 47% after 1 day and 43% after 3 days. Cortical cytosolic prostaglandin E2-9-ketoreductase activity was found to be decreased by 36% and 76% after 1 and 3 days respectively. No significant changes were noted in cortical cytosolic prostaglandin E2-15-hydroxydehydrogenase activity after 3 days. Cortical tissue levels of prostaglandin E2 increased by 500% at the end of 3 days. These data demonstrate that in nephrotoxic acute renal failure, decreased prostaglandin metabolism (i.e., prostaglandin E2-9-ketoreductase activity) can result in increased tissue levels of prostaglandin E2 in the absence of increased prostaglandin synthesis and suggest that alterations in prostaglandin metabolism may be an important regulator of prostaglandin activity in acute renal failure.

Amphotericin B nephrotoxicity: increased renal resistance and tubule permeability

Two groups of rats received amphotericin-B (Amp). One group (AA) received a single acute dose of 1 mg/kg i.v. The second (CA) received 10 mg/kg i.p. daily for 4 days. In AA rats, measurements 1 to 5 hr after Amp were compared with their own preinfusion values. Inulin clearance, (CIn, 4.5 ml X min-1 X kg-1 per kidney pre vs. 1.3 post), renal plasma flow (RPF, 12.0 ml X min-1 X kg-1 vs. 7.4), and the estimated pressure in the glomerular capillaries (Pgc, 52 mm Hg vs. 40), were all significantly decreased while renal vascular resistance (5.2 mm Hg/ml vs. 12.0) was increased. Only 45% of the 3H-inulin injected into surface tubules was recovered in the urine as contrasted with 100% recovery before injection. This suggests that tubule permeability was increased, but there was no histologic evidence of renal tubule necrosis. Twenty-four hours after intravenous Amp, CIn and RPF returned to normal. Data from CA rats were compared with values from sham-treated pairfed (PF) control rats. Again, CIn (4.22 ml X min-1 X kg-1 in PF vs. 2.69 in CA), RPF (16.1 ml X min-1 X kg-1 vs. 8.3), and Pgc (48 mm Hg vs. 38) were decreased, and renal vascular resistance (4.9 mm Hg/ml vs. 8.0) was increased. The recovery of 3H-inulin in the urine was slightly, but significantly, decreased (96% vs. 83%). These findings demonstrate that Amp decreases renal function by at least two mechanisms. An increase in renal vascular resistance is most important, although increased tubule permeability with a "backleak" of tubule fluid also contributes to renal dysfunction, particularly after intravenous Amp.

Hemodynamic and single nephron function during the maintenance phase of ischemic acute renal failure in the dog

We studied ischemic acute renal failure in 28 dogs by micropuncture, microsphere, morphologic, and whole kidney hemodynamic techniques, 18 to 24 hours after the renal artery was clamped (clamping time, 60 to 90 min). Before the artery was clamped, renal blood flow (RBF) averaged 3.49 +/- (SEM) 0.23 ml/min x g and was not significantly different (3.70 +/- 0.34 ml/min x g) 18 hours after the ischemic episode. RBF autoregulatory capability was, however, significantly reduced. Fractional outer cortical blood flow decreased slightly from 41 +/- 2 to 36 +/- 3% (P less than 0.05) postischemia. Single nephron glomerular filtration rate (SNGFR) was highly variable from one animal to the next and ranged from 0 to 87 nl/min (mean, 36 +/- [SEM] 7 nl/min) in a manner similar to whole kidney inulin clearance, which ranged from 0 to 0.56 ml/min x g (mean, 0.30 +/- 0.05 ml+min x g). The correlation coefficient between SNGFR and inulin clearance was highly significant, indicating an association between SNGFR and whole kidney GFR. Proximal tubule pressure (PTP) averaged 20 +/- (SEM) 1 mm Hg. In 6 dogs, the glomerular filtration coefficient (Kf) was determined by measurements of stop-flow pressure, colloid osmotic pressure, SNGFR, PTP, and single nephron filtration fraction, Kf was below that obtained for control animals. Scanning electron microscopy (SEM) studies indicated that the endothelial fenestrations were reduced in number and size. These studies suggest that one major characteristic of ischemic nephropathy in the dog is a derangement in the filtration process. The maintenance of RBF in the postischemic phase may occur by utilization of the autoregulatory reserve of the renal vasculature.

Preliminary observations concerning the effect of dopamine on uranyl nitrate induced renal failure

Dopamine infusion, when commenced 24 h after the insult, was ineffective in modifying the course of uranyl nitrate induced renal failure in rabbits.

Sodium-chloride-induced protection in nephrotoxic acute renal failure: independence from renin

It has been shown that the severity of experimentally induced acute renal failure (ARF) is inversely related to dietary sodium chloride intake, and the effects have been attributed to the concurrent changes in renal renin. In the current study, renal renin of rats was increased by chronic sodium deprivation and decreased by chronic sodium loading and DOCA administration. In two nephrotoxic models (mercuric chloride, uranyl nitrate), giving previously sodium-deprived rats 1% sodium chloride to drink for 48 hours prior to ARF induction greatly attenuated the severity without any reduction in their high renal renin. Conversely, giving previously sodium-loaded rats tap water to drink for 4 to 5 days prior to AFR induction greatly enhanced the severity without any increase in their subnormal renal renin. Therefore, the changes in severity of ARF resulting from changes in dietary sodium are not mediated by changes in renal renin. Significant inverse correlations were found between mean peak BUN values during the follow-up period (5 to 7 days) and the 24-hour urinary sodium excretions prior to ARF induction in both models, suggesting that sodium intake and/or excretion at the time of induction is a good predictor of the severity. The effects of sodium chloride in both models were predominantly expressed during the maintenance phase, and consisted of attenuation of the severity (both models) and hastening of the recovery (mercuric chloride model). Possible mechanisms by which dietary sodium produced its effects, independently of its effects on the renin-angiotensin system, are discussed.