Experimental acute renal failure induced by uranyl nitrate in the dog

Prediction of Pharmacokinetics of Antibiotics in Patients with End-Stage Renal Disease

A novel and convenient method to predict the pharmacokinetics of several kinds of antibiotic agents in patients with end-stage renal disease (ESRD) was examined based on the in vitro extraction ratios and pharmacokinetic parameters in healthy volunteers. The dializability of 17 antibiotic agents in 4% human serum albumin solution were determined using a high-performance hemodialytic membrane for clinical use. We assumed that the off-hemodialysis clearance approximated the non-renal clearance, while the on-hemodialysis clearance was considered to be sum of the off-hemodialysis clearance and the hemodialytic clearance. The estimated on- and off-hemodialysis clearances were compared with the ones observed in ESRD patients. In order to confirm the method prospectively, an in vivo pharmacokinetic study was performed in dogs with mercury chloride-induced experimental renal failure. The in vitro extraction ratios of 9 beta-lactams were broadly ranged from 10.9 to 75.6% depending on their physicochemical properties. In contrast, those of the other antibiotics were consistent with their chemical classes: 60.5-63.2% for fluoroquinolone, 48.8-51.1% for aminoglycoside and 18.7-25.6% for glycopeptide. Both the estimated on- and off-hemodialysis clearances of the 17 antibiotics coincided well with the observed values in the literature, regardless of their physicochemical and pharmacokinetic properties. The validity and applicability of this method to three cefems, cefmetazole, cefotaxime and cefoperazone, was prospectively confirmed in the animal study. In conclusion, this new method enables the prediction of the on- and off-hemodialysis clearances of several kinds of antibiotics in ESRD patients from minimal information of their pharmacokinetics in healthy subjects and their in vitro dializability.

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.

North American opossum Didelphis virginiana as a fetal nephrotoxicity model: histologic and ultrastructural assessment of uranyl nitrate (UN)-induced damage

We have used our opossum model of fetal nephrotoxicity to investigate uranyl nitrate-induced morphologic changes in the developing kidney. The present study establishes a renal dose response curve for the uranyl nitrate (UN). We find that pups treated with nonlethal doses of UN do not demonstrate growth retardation compared to saline-treated controls. The kidneys of UN-treated pups are heavier than the control animals, an effect less apparent the longer the pups are followed. A low dose of 60 mg/kg of UN administered to small pups causes slight histologic derangement but nevertheless more change than the same dose administered to larger more mature pups. Using a dose of 100 mg/kg of UN that effectively causes nonfatal renal disruption, we examined the kidneys from 4 to 42 days following injection. We find that tubular dilation and epithelial necrosis starts soon after treatment (day 4) and reaches its maximum during the second and third week (11 and 22 days). Architectural restoration appears complete by the end of the third week. By electron microscopy, UN induces sequential structural damage with loss of proximal tubule brush border, epithelial necrosis with intact basement membranes and regeneration at 4, 11, and 22 days. Residual tubular mitochondrial damage is present at 42 days in spite of histologically normal tubules. No apparent lesions are seen in glomeruli. Fibroblastic interstitial proliferation in UN-treated kidneys at 11 days is not followed by appreciable fibrosis when assessed at 22 and 42 days. As the structural changes caused by 100 mg/ml UN administration in fetal opossum kidneys are reversible, this is a useful model to study the molecular mediators responsible for this form of renal damage and repair.

Thyroid hormone profiles in experimental acute renal failure

Thyroid hormone profiles were determined in two groups of dogs made uremic, either by i.v. uranyl nitrate 10 mg/kg BW injection or by bilateral ureteral ligation, and in one group of sham-operated animals. Each group consisted of 6 dogs and served as its own control. From blood samples taken in 12-h intervals up to 144 h for uranyl nitrate-injected dogs and 96 h for operated dogs, serum levels of T4, T3, fT4, fT3, rT3, and cortisol were measured by radioimmunoassays. The results obtained in both groups of uremic dogs showed an initial sharp fall of T4, T3, fT4, and fT3 followed by a plateau or retarded decrease. In sham-operated dogs the fall of these hormones was slight and of short duration. Reverse T3 had a tendency to increase in all groups examined, but a significant elevation was recorded only after bilateral ureteral ligation. In this group cortisol serum levels were found the highest, being also significantly increased in the other two groups. The temporal coincidence of the most marked alterations in T3, rT3, and cortisol serum concentrations indicates a significant role of stress in thyroid dysfunction. Although serum creatinine rise and weight loss were not parallel with thyroid hormone alterations, the involvement of uremic compounds and malnutrition in this process is also quite clear. Thus, the data presented suggest simultaneous influences of uremic toxins, stress, and malnutrition on the induction of thyroid dysfunction in dogs made uremic by uranyl nitrate injection or bilateral ureteral ligation.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal nephrotoxicity

Investigation of fetal nephrotoxicity by maternally administered nephrotoxins is hampered by many constraints, including the maternal effects of the nephrotoxin, the ability of the nephrotoxin to cross the placenta and the difficulties associated with direct fetal intervention. In the pouch young of the North American opossum, Didelphis virginiana, we describe the toxic effects of a heavy metal on the immature metanephric kidneys. Varying doses of uranyl nitrate, a heavy metal salt, were administered to opossum pups in the pouch approximately 20 days after birth and the kidneys were harvested 3 to 12 days later for histological analysis. Group 1 consisted of 4 untreated and 5 saline treated pups. Group 2 (9 pups) received 10 to 15 mg./kg. intraperitoneal uranyl nitrate. Group 3 (6 pups) were given a uranyl nitrate dose of 25 mg./kg. Group 4, the high dose group, received either 58 mg./kg. (3 pups) or 87 mg./kg. (3 pups) of intraperitoneal uranyl nitrate. Group 1 kidneys demonstrated no pathological changes except for some mild renal tubular vacuolization seen in the saline treated animals. In group 2 tubular dilatation and necrosis were present 3 days after treatment; tubular regeneration could be seen by day 7. In group 3 glomerular cystic changes, interstitial fibrosis and tubular regeneration were present by day 7. Some restoration of normal architecture occurred by day 12 with fibrosis apparent. Group 4 animals demonstrated much more pronounced cystic changes of glomeruli and tubules as early as day 5 with marked interstitial fibrosis and prominent tubular regeneration. By day 12 group 4 pups continued to demonstrate significant and severe glomerular and tubular cystic changes with marked interstitial fibrosis. Inflammation, although present in all groups (except control), was never prominent. This first description of the effect of heavy metal toxicity on the immature metanephric kidney could provide an insight into the mechanisms of disordered kidney growth.

Theoretical analysis of pathogenetic mechanisms in experimental acute renal failure

A network thermodynamic model of glomerular dynamics has been employed to determine the degree of change in individual glomerular vascular resistances, hydraulic conductivity and proximal tubule pressure that, singly or in concert, could lower GFR to the degree expected in experimental acute renal failure (ARF). In both the rat and dog, the analysis shows that filtration failure is not achieved until preglomerular resistance (RA) is increased at least twofold or postglomerular resistance (RE) is decreased by 74% or more with all other determinants held at control values. Tubular obstruction alone will not provide failed filtration until tubule pressure is increased to 30 to 40 mm Hg in the rat and 44 mm Hg in the dog. A much smaller change in tubular pressure can contribute greatly to the development of filtration failure, however, when occurring in association with major change in individual vascular resistances. Glomerular capillary resistance must be increased to a value more than twice the normal sum of RA and RE (greater than fivefold in the dog), and glomerular capillary hydraulic conductivity lowered to below 5% of control, as isolated changes, before full filtration failure is approached. There is no reason to believe that most forms of ARF relate to only a single abnormality, however, and the effect of concomitant changes in individual resistances, hydraulic conductivity and proximal tubule pressure on glomerular filtration and blood flow is presented in the text and figures. A possible mechanism by which altered blood viscosity at the efferent arteriole may contribute to ARF is discussed and quantified. The degree of change in any determinant required to exert a given effect on filtration is independent of etiology, thus rendering the results of this analysis equally valid for any other pathological event which causes a significantly reduced GFR in the rat or dog.

Attenuation of nephrotoxic acute renal failure in the dog with angiotensin-converting enzyme inhibitor (SQ-20,881)

Angiotensin-converting enzyme inhibitor was used in dogs with uranyl nitrate-induced acute renal failure to evaluate (1) a possible protective effect of angiotensin blockade and (2)the role of angiotensin II in the generation of renal failure in this model. Angiotensin-converting enzyme inhibitor treatment attenuated the fall in glomerular filtration rate and renal blood flow during the first 6 hours after injection of the nephrotoxic agent. A protective effect of similar magnitude was observed whether angiotensin-converting enzyme inhibitor treatment preceded, or shortly followed, the administration of uranyl nitrate. This indicates that angiotensin-converting enzyme inhibitor delivery to its intrarenal site of action remains effective after administration of the nephrotoxin. In addition, protection of glomerular filtration rate correlated with sodium and renal solute excretion. However, combined treatment with angiotensin-converting enzyme inhibitor and furosemide enhanced solute excretion but did not further improve the protection of renal function. Finally, the protective effects of angiotensin-converting enzyme inhibitor on renal function and hemodynamics were abolished by intravenous indomethacin. In conclusion, early, continuous blockade of angiotensin II protects partially against th initiation of acute renal failure. These findings support a major pathogenic role for angiotensin II in the generation phase of acute renal failure in this model. Furthermore, they suggest that an imbalance between vasoconstrictive (angiotensin II) and vasodilating factors (prostaglandins) may be operative in the early phase of uranyl nitrate-induced acute renal failure in the dog.

Dissociation of glomerular filtration and renal blood flow in HgCl2-induced acute renal failure

This study evaluates the role of early renal vasoconstriction in the pathogenesis of mercuric chloride (HgCl2)-induced acute renal failure (ARF) in the dog. Within 3 hr after mercury, glomerular filtration rate (GFR), from 45 +/- 4 25 +/- 2 ml/min, and renal blood flow (RBF), from 268 +/- 22 to 161 +/- 19 ml/min, decreased simultaneously. A rise in diuresis and urinary solute excretion occurred. Morphological and functional studies excluded a major role for tubular leakage or obstruction. An attempt was made to prevent the early renal vasoconstriction, by the administration of Haemaccel, a plasma volume expander, alone or in combination with phentolamine. In both settings the fall in RBF after mercury was prevented. Haemaccel volume expansion alone provoked a significant rise in GFR before HgCl2, but the GFR fell by 29% 3 hr after HgCl2. The Haemaccel/phentolamine combination had no influence on pre-mercury GFR values. In this group, a decrease of GFR by 44% was noted 3 hr after mercury. In conclusion, changes in GFR and renal hemodynamics can be dissociated in the early phase of nephrotoxic ARF. The fall in GFR can be attributed either to a decrease in glomerular ultrafiltration capacity and/or changes in glomerular afferent and efferent resistances, leading to a decrease in glomerular hydrostatic pressure.

Nephrotoxicity of cis-diamminedichloride platinum (CDDP) during remission-induction and maintenance chemotherapy of testicular carcinoma

We studied renal function in nine patients with disseminated testicular carcinoma before and after remission-induction and maintenance therapy with a drug combination containing cis-platinum. The median glomerular filtration rate (GFR) decreased during remission-induction therapy from 146 to 118 ml/min. No effect of cumulative toxicity on the median GFR was found during maintenance therapy, nor did the median GFR improve. The median effective renal plasma flow (ERPF) decreased during the total period from 705 to 514 ml/min. No significant changes in median filtration fraction (FF) and serum creatinine were observed. It is suggested that intrarenal hemodynamic effects are important in the nephrotoxicity of cis-diamminedichloride platinum (CDDP).

Loss of the glomerular contractile response to angiotensin in rats following myohemoglobinuric acute renal failure

To examine the state of the glomerulus in rats protected from acute renal failure (ARF) by prior insult, we measured the contractile responses of isolated glomeruli to angiotensin II (AII) and dibutyryl cyclic AMP (DBcAMP). In healthy rats, both agents induced a dose-related fall in glomerular diameter (P less than 0.001). Saralasin, the angiotensin antagonist, blocked the glomerular response to AII totally and to DBcAMP partially. Two weeks following ARF induced with 50% glycerol (10 ml/kg, im), azotemia had reversed and the nephrotoxic effect of mercuric chloride (4.7 mg/kg, sc) was blunted, as anticipated. AII did not reduce glomerular size, but the response to DBcAMP was sustained at this time. To determine the specificity of the loss of the glomerular response to AII, we also assessed the effects of an AII infusion (1 microgram/kg/min) on blood pressure and renal blood flow. There was a substantial rise in blood pressure (control, 104 +/- 11.8 mm Hg; AI, 131.0 +/- 5.3 mm HG; P less than 0.001) and fall in renal blood flow (control, 2.45 ml/g per min; AII, 0.81 +/- 0.10 ml/g per min; P less than 0.025). Vascular responsiveness to AII was preserved at a time when glomeruli were totally unresponsive and rats were resistant to ARF. The loss of glomerular contractility may, in part, account for the protection from ARF seen in this model: if so, glomerular abnormalities may play a pathogenetic role.

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.

Synergism of dopamine plus furosemide in preventing acute renal failure in the dog

The protective effects of a combination of dopamine and furosemide were studied in dogs during the initial phase of acute renal failure (ARF) induced by intravenous uranyl nitrate (10 mg/kg). Fifteen minutes after injection of the nephrotoxin, and infusion of dopamine (3 micrograms/kg/min), furosemide (1 mg/kg/bolus followed by 1 mg/kg/hr), or both drugs simultaneously were given for 6 hours. Exogenous creatinine clearance was measured for 6 hours, and the intrarenal blood flow was measured with radioactive microspheres before and 3 hours after the induction of ARF. Treatment with both dopamine and furosemide produced renal vasodilatation, high urine flow rate, and attenuation of the fall in GRF seen in untreated animals. In contrast, single use of dopamine or furosemide was totally ineffective in producing renal vasodilation, a diuresis, or the maintenance of the GFR. These data indicate that dopamine plus furosemide have a synergistic effect in preventing the early pathophysiologic changes associated with ARF in this animal model. Maintenance of a high GFR correlated best with the enhancement of solute excretion and urine flow rate. Potential protective effects of dopamine plus furosemide in other models of ARF deserve careful investigation.

Nephron function of the transplanted rat kidney

Tubular function in the early phase (one to three hours) after transplantation of rat kidneys was analyzed with respect to glomerular filtration, vascular and tubular pressures, and excretory variables. Kidneys exposed to a short period of cold ischemia (two hours) functioned almost normally, except for a polyuria. After 12 and 16 hr of cold ischemia, nephron heterogeneity appeared with 1) "normal" tubules, 2) dilated tubules, and 3) collapsed tubules. In the "normal" tubules, the pressure was increased to 20 mm Hg, and the filtration was reduced in proportion to the mean net driving force. The dilated tubules had no filtration due to a more or less complete tubular obstruction, probably located in the thin loop of Henle and in the collecting ducts. The collapsed tubules had no filtration due to glomerular ischemia, which in turn might be the consequence of afferent arteriolar constriction. The total GFR was greatly reduced since only the "normal" tubules contributed to the total filtration. Concentrating ability and potassium secretion were also impaired. We interpreted this impairment as being due to medullary dysfunction, which would explain the isosthenuria and the impaired potassium transport.

The early phase of experimental acute renal failure. III. Tubologlomerular feedback

Experiments were designed to determine whether tubologlomerular feedback, which modifies nephron filtration rate in response to alterations in the macula densa sodium chloride concentration, was still apparent in the initiation phase of various types of acute renal failure. The response of the glomerulus to changes in the macula densa stimulus was evaluated in haeme pigment, ischaemic and nephrotoxic induced renal damage by measuring early proximal flow rates. The sodium chloride concentration at the macula densa was varied between low values and isotonicity in two ways: firstly, by interruption of flow through the loop of Henle, followed by orthograde perfusion with Ringer's solution; secondly, by retrograde perfusion of the loop of Henle with isosmotic mannitol or Ringer's solution. In all nephrons examined, filtration rate was inversely correlated to the macula densa sodium chloride concentration, except during orthograde perfusion with 10(-4) M furosemide in Ringer's solution, when, despite the high sodium chloride concentration, filtration rate remained high. It is concluded that the mechanism of tubuloglomerular feedback is viable after the onset of compromised renal function, and may, as postulated, account for the reduction in blood flow and nephron filtration rate occurring in acute renal failure.

The early phase of experimental acute renal failure. I. Intratubular pressure and obstruction

Tubular obstruction in acute renal failure, postulated to cause the restricted excretory function, is suggested by raising intratubular pressure, to lower effective filtration pressure and diminish urine output. To examine the applicability of the obstruction hypothesis to the pathogenesis of experimental acute renal failure, proximal intratubular pressure and renal function were measured after renal insults of different origins and severity. Obstruction in acute renal failure kidneys should manifest itself as an increase in intratubular pressure for a least 12 h, for within this time period following ureteral occlusion, elevated pressures were found to reflect obstruction. The consistent existence of raised proximal intratubular pressure in acute renal failure kidneys could not be detected; ischaemic and nephrototoxic models were found in which no rise in intratubular pressure could be demonstrated. The oliguric nature of acute renal failure kidneys could not be verified; ischaemic and nephrotoxic models were found in which urine output was either normal or enhanced. Only for methaemoglobin induced renal failure were raised intratubular pressure, oliguria and casts concurrent. It is concluded that obstruction is not a consistent feature of experimental acute renal failure and that the obstruction hypothesis may be specifically applicable to only a few models, which include haeme pigment and folic acid induced renal failure.

Effect of dithiothreitol on mercuric chloride- and uranyl nitrate-induced acute renal failure in the rat

The current study was undertaken to examine the effects of dithiothreitol (DDT), a sulfhydryl-reducing agent and heavy metal chelator, on the course of heavy metal-induced acute renal failure in the rat. Groups of rats in metabolic cages received uranyl nitrate (UN) alone, UN plus DTT, mercuric chloride (HgCl2) alone, and HgCl2 plus DTT. UN injected alone produced azotemia, decreased creatinine clearance, and rising fractional sodium excretion over the 48 hr of study. These effects of UN on renal function were not observed when DTT was administered 30 min after UN injection. Qualitatively similar results were obtained with HgCl2-induced acute renal failure. Groups of rats were killed at 6 hr after UN plus DTT, HgCl2 alone, or HgCl2 plus DTT; and determinations of plasma renin activity (PRA) and renin activities of the superficial and deep juxtaglomerular apparatus (JGA) were performed. PRA's and JGA renins were increased in animals receiving either UN or HgCl2 alone, but not in the rats receiving both DTT and UN or HgCl2. The effect of DTT on distribution of 203Hg was also examined. Treatment with DTT did not alter the renal accumulation of 203Hg, suggesting that this agent does not act by limiting renal exposure to the heavy metals. Thus, DTT ameliorates the course of heavy metal-induced ARF, and this effect is associated with prevention of heavy metal-induced alterations in sodium excretion and renin-angiotensin system activity.

Normal renocortical blood flow in experimental acute renal failure

Renal cortical blood flow of rats with postischemic, myohemoglobinuric, and mercury-induced acute renal failure was measured by the hydrogen washout technique using implanted platinum electrodes. Total renal blood flow was determined by venous cannulation in separate series of rats. The values obtained with the two methods were in excellent qualitative agreement (r=0.99, P less than 0.001), although venous cannulation gave values that were constantly lower than those calculated for whole kidney from the cortical flow rate and assumed cortical mass. Myohemoglobinuria produced by glycerol injection caused cortical blood flow to fall from a control value of 7.37+/-0.23 (SEM) ml/min X g of cortex to approximately one-half that value for four hours after injection (P less than 0.001). Flow rates 12 and 24 hr after glycerol injection were 85% (P less than 0.001) and 90% (P less than 0.05) of control, respectively. Cortical flow was reduced to 5.49+/-0.39 (SEM) ml/min X g of cortex four hours after release of one hour's total bilateral renal arterial occlusion (P less than 0.001), but rose to normal within 24 hr. Poisoning with 4.7 mg/kg of body wt of mercuric chloride produced a cortical blood flow value that was 30% higher than control 24 hr after injection (P less than 0.01), while a 12 mg/kg of body wt dose gave a normal flow value. Inulin clearance was severely depressed in all models at all study times. Thus, in contrast to human acute renal failure, marked renal cortical ischemia is not an essential feature of these different forms of murine acute renal failure.

Cardiac output and renal blood flow in glycerol-induced acute renal failure in the rat

Cardiac output (CO) and renal blood flow (RBF) were simultaneously evaluated by the microsphere method in water-drinking and chronic saline-drinking rats at 3, 12 and 24 hours after induction of acute renal failure by glycerol injection. Threee hours after glycerol injection CO and RBF decreased to 36% and 20% of the respective controls in water-drinking rats and to 41% and 24% of the controls in saline-drinking rats. Renal vascular resistance (RVR) increased significantly in both groups at this time. Isoncotic plasma expansion (3% of body weight) restored the RBF and RVR to normal in water-drinking rats 3 hours post-glycerol injection, althought CO increased to only 70% of the control. Twelve hours after glycerol injection, CO and RBF returned to normal in saline-drinking rats, whereas they remained lower than controls in water-drinking rats. Twenty-four hours post-glycerol injection, when acute renal failure was evident as indicated by blood urea nitrogen (BUN) values of 116.9 and 63.8 mg/100 ml in water- and saline-drinking rats, respectively, CO and RBF returned to normal, except that the CO of of water-drinking rats was slightly higher than control. Thus, we conclude that decreased CO is an important determinant of the early decrease in renal perfusion in glycerol-induced acute renal failure. Furthermore, the observed earlier return of CO and RBF to normal in saline-drinking rats may be partly responsible for reproducing the severity of acute renal failure.

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

The role of renal hemodynamic alterations in the curtailment of renal function was studied in rabbits with uranyl acetate-induced acute renal failure. The day following the i.v. injection of uranyl acetate (2 mg/kg of body wt), renal blood flow (RBF) and clearance of creatinine (Ccr) decreased to approximately 60 and 20% of controls, respectively. Intracortical fractional flow distribution, estimated by radioactive microsphere method, did not change. The extraction ratio of para-aminohippurate (EPAH) decreased and the renal extraction of sodium (CNa/Ccr) increased, with minimal structural change in the kidney. Urine output increased to two to three times that of the control. After three days oliguria appeared despite complete recovery of RBF. The zonal flow redistributed toward the deep cortex. CCr and EPAH reached their minimums, concomitantly with tubular necrosis and intratubular casts. After seven days animals could be divided into the oliguric and diuretic groups. CCr and EPAH were higher in the diuretic group, while there was no significant difference in RBF and the flow distribution between groups. Regeneration of damagee tubular cells was found in the diuretic group but not in the oliguric group. The findings suggest the minor roles of RBF and the intracortical flow distribution, and a fundamental role of back leakage of filtrate across damaged tubular epithelium in the maintenance of reduced CCR and urine output during the oliguric stage in rabbits with uranyl acetate-induced renal failure.

Effect of variation in dietary NaCl intake on total and fractional renal blood flow in the normal and mercury-intoxicated rat

We studied the effect of different chronic (3-4 weeks) dietary salt intakes on intrarenal hemodynamics of normal and mercury-intoxicated rats. Cardiac output (CO), total renal blood flow (RBF), and the zonal perfusion rate in the outer cortex (OC) and inner cortex (IC) were measured by the radioactive microsphere method. The distribution of cortical blood flow was calculated as the distribution index (DI), which reflects the ratio OC/IC. Rats were placed on a high salt diet (group I), intermediate salt diet (group II), or low salt diet (group III). For each group control rats (subgroup A) and mercury-intoxicated rats (subgroup B) were studied. No effect of the different salt intakes on the DI could be detected. The DI in group IA was 2.35 +/- 0.14; in IIA, 2.40 +/- 0.16; and in IIIA, 2.38 +/- 0.09 (P greater than 0.05). After mercury injection RBF changed from 5.32 +/- 0.36 ml/g.min(-1) (IIA) to 3.31 +/- 0.20 ml/g.min(-1), IIB and from 4.32 +/- 0.11ml/g.min(-1) (IIIA) to 1.98 +/- 0.10 ml/g.min(-1) (IIIB) P less than 0.01). The DI was lowered to 1.53 +/- 0.06 (IIB) (P less than 0.05) and to 1.16 +/- 0.10 (IIIB) (P less than 0.01). In both IIB and IIIB a marked elevation of the blood urea was noted (IIB = 97 +/- 9 MG/100 ML AND IIIB = 182 +/- 25 mg/100 ml). In group IB no effect on RBF, OC, IC, or DI could be observed (for all values, P greater than 0.05) despite similar histological renal lesions. Group IB rats also had normal blood urea levels (31 +/- 6 mg/100 ml;P greater than 0.05). We conclude (1) that variations in dietary salt intake appear to have no detectable effect on the intracortical blood flow distribution; and furthermore (2) that the mercury-induced acute renal failure (ARF) is characterized hemodynamically by a total renal and preferential outer cortical ischemia and that chronic salt loading prevents the ARF while preserving normal renal perfusion.

The vascular basis for acute renal failure in the rat. Preglomerular and postglomerular vasoconstriction

Myohemoglobinuric acute renal failure (ARF) was induced in dehydrated, salt-deficient, salt-loaded, and untreated rats by intramuscular injection of glycerol, and the renal vasculature was studied after 24 hours. Kidneys were prepared for examination by rapid freezing in vivo to -160 degrees C and freeze substitution in -80 degrees C alcohol, and by perfusion fixation with 1% glutaraldehyde in Ringer's solution at 120 mm Hg. Frozen kidneys were examined by light microscopy after paraffin and epoxy resin embedding. Techniques used in examining the perfusion-fixed kidneys were: (1) vascular injection with silicone rubber and clearing in glycerol, (2) electron microscopy, and (3) morphometric evaluation of lumen to wall area ratios of glomerular arterioles. Kidneys of all rats with ARF showed renal cortical arterial and glomerular arteriolar (afferent and efferent) vasoconstriction. The degree of constriction, estimated by lumen to wall ratios, correlated with the degree of azotemia (r = -0.71; P less than 0.001). Differences between all ARF groups and respective controls were highly significant (P less than 0.001). Vasoconstriction was maximal in the dehydrated group, intermediate in the untreated and Na-deficient rats, and lowest in the salt-loaded animals. Glomerular and peritubular capillaries were patent and free of endothelial swelling or thrombi. Glomerular basement membranes and epithelial foot processes showed no morphological alterations. The observations suggest that marked pre- and postglomerular vasoconstriction occurs in established myohemoglobinuric ARF, that it is related to azotemia, and that mechanical vascular obstruction does not play a major role in this experimental model.

Pathophysiology of a nephrotoxic model of acute renal failure

Studies were performed in the dog to determine the mechanism of the renal functional impairment which follows the administration of the nephrotoxic agent, uranyl nitrate. In the first series of 28 experiments, total renal blood flow was determined with the radioactive microsphere method before and after uranyl nitrate administration, 10 mg/kg. Total blood flow fell from 199 to 121 ml/min 6 hr after administration of uranyl nitrate (P less than 0.001) but was unchanged 48 hr after administration of the drug. Yet the blood urea nitrogen concentration had increased from a control value of 13 to 120 mg/100 ml at 48 hr (P less than 0.001). Since renal blood flow was normal at 48 hr, micropuncture studies were performed to further evaluate the mechanism of the renal impairment. In the first group of nine studies using a 10 mg/kg dose of uranyl nitrate, nephron glomerular filtration rate (GFR) was reduced 37% while total kidney GFR averaged less than 1% of normal. A similar disparity between superficial and total GFR was noted after a 5 mg/kg dose even though urine flow was comparable to values found in normal hydropenic dogs. Proximal tubular transit time and intratubular pressure were normal. The recovery of 3H-inulin injected into the proximal tubule was 97% in normal dogs and 14% in uranyl nitrate dogs (P less than 0.001). Since there was no difference between early and late proximal tubular nephron GFR, it was suggested that the pars recta, the segment most severely involved histologically, was the main site of inulin leak. Scanning electron microscopy revealed an alteration in epithelial architecture which may have accounted, at least in part, for the diminution in nephron GFR. These studies are interpreted to indicate that the impairment in renal function in this model is due to both leakage of filtrate across damaged tubular epithelium and a modest decrease in nephron GFR.

The mechanism of acute renal failure after uranyl nitrate

Administration of 25 mg/kg uranyl nitrate (UN) to rats leads to a brief period of polyuria followed by progressive oliguria with death at 5 days. Factors that determine glomerular filtration rate (GFR) were examined in control Munich-Wistar rats (n equals 16) and 2 h after either 15 mg/kg (n equals 8) or 25 mg/kg (n equals 7) of UN (i.v.) utilizing direct measurements of hydrostatic and oncotic pressures and plasma flow. Total kidney GFR was reduced to 47% of control in the low dose group and to 21% in the high dose group. The simultaneous nephron filtration rate (sngfr) was 28.6 plus or minus 0.8 nl/min/g kidney wt in control, 29.1 plus or minus 1.0 in the low dose group, and 18.1 plus or minus 1.2 (P less than 0.001) in the higher dose group. This disparity in UN effect upon GFR and sngfr was due to tubular back-diffusion of solute through damaged epithelia beyond the early proximal tubule as demonstrated by microinjection of inulin and mannitol in the proximal tubule. Inulin "leak" persisted at 6 h after UN when tubular pressure had returned to normal. Comparison of sngfr measured in early vs. late proximal tubule revealed no difference after high dose UN, suggesting no significant leak of inulin from the early proximal tubule, and that the decreased sngfr was due to primary reductions in ultrafiltration. Nephron plasma flow was equal to control at both doses of UN. Also directly measured hydrostatic pressure gradient across the glomerular capillary was not changed. The effective filtration pressure achieved equilibrium in control of animals but became significantly positive at the efferent end of the capillary at both doses of UN and increased. Total glomerular permeability (LpA) was progressively reduced from control (0.089 plus or minus 0.005 nl/s/g kidney wt/mm Hg) at low dose UN (0.047 plus or minus 0.013) and high dose 0.024 plus or minus 0.003 nl/s/g kidney wt/mm Hg). Therefore UN decreases GFR by two mechanisms: (1) tubular damage leading to back-diffusion of solutes and (b) a primary reduction in sngfr due to reduced LpA.