Uranyl nitrate-induced acute renal failure in the rat: micropuncture and renal hemodynamic studies

Kidney Injury after Intravenous versus Intra-arterial Contrast Agent in Patients Suspected of Having Coronary Artery Disease: A Randomized Trial

Background In the absence of randomized studies, it has been controversial whether the likelihood of acute kidney injury (AKI) differs between intravenous and intra-arterial contrast agent administration. Purpose To compare intravenous versus intra-arterial contrast agent administration in relationship to AKI and analyze the association between AKI and chronic kidney disease (defined as at least mildly decreased estimated glomerular filtration rates [eGFRs]). Materials and Methods This was a prospective study (ClinicalTrials.gov: NCT00844220) that involved randomizing participants with atypical chest pain and suspected coronary artery disease (CAD) between February 2009 and August 2015 to undergo coronary CT angiography with intravenous contrast agent administration or cardiac catheterization angiography with intra-arterial contrast agent administration. This prespecified secondary analysis compared AKI (serum creatinine increase of ≥ 25% or 0.5 mg/dL after 18-24 or 46-50 hours) determined by blinded investigators using absolute differences and relative risks, including two-sided 95% confidence intervals (CIs). Results A total of 320 participants (163 [50.9%] women; mean age, 60 years ± 11) were included. Baseline eGFR did not differ between the CT angiography group (84.3 mL/min/1.73 m² ± 17.2) and the catheterization group (87.1 mL/min/1.73 m² ± 16.7) (P = .14). AKI occurred in nine of 161 participants in the CT angiography group (5.6%; 95% CI: 3%, 10%) and in 21 of 159 participants in the catheterization group (13.2%; 95% CI: 9%,19%) (relative risk, 2.4; 95% CI: 1.1, 5.0; P = .02). Also in the subgroup of participants without obstructive CAD, in those not requiring coronary interventions, AKI was more common in the catheterization group (11.9%; 95% CI: 8%, 19%) than in the CT angiography group (4.3% [95% CI: 2%, 9%]; difference, 7.7% [95% CI: 1.3%, 14.1%]; relative risk, 2.8 [95% CI: 1.1, 7.0]; P = .02). Obstructive CAD (odds ratio [OR]: 2.7 [95% CI: 1.1, 6.6]; P = .02), femoral catheter access (OR: 2.5 [95% CI: 1.1, 5.6]; P = .04), and cine ventriculography were associated with AKI (OR: 2.3 [95% CI: 1.0, 4.9]; P = .03). In multivariable analysis, the presence of postcontrast AKI was associated with chronic kidney disease (hazard ratio: 12.4 [95% CI: 4.5, 34.6]; P < .01). Conclusion Acute kidney injury was more common after cardiac catheterization than after CT angiography in this prospective randomized study of patients suspected of having coronary artery disease. © RSNA, 2019 Online supplemental material is available for this article. See also the editorial by Einstein and Newhouse in this issue.

Role of intratubular pressure during the ischemic phase in acute kidney injury

Acute kidney injury (AKI) induced by clamping of renal vein or pedicle is more severe than clamping of artery, but the mechanism has not been clarified. In the present study, we tested our hypothesis that increased proximal tubular pressure (P_t) during the ischemic phase exacerbates kidney injury and promotes the development of AKI. We induced AKI by bilateral clamping of renal arteries, pedicles, or veins for 18 min at 37°C, respectively. P_t during the ischemic phase was measured with micropuncture. We found that higher P_t was associated with more severe AKI. To determine the role of P_t during the ischemic phase on the development of AKI, we adjusted the P_t by altering renal artery pressure. We induced AKI by bilateral clamping of renal veins, and the P_t was changed by adjusting the renal artery pressure during the ischemic phase by constriction of aorta and mesenteric artery. When we decreased renal artery pressure from 85 ± 5 to 65 ± 8 mmHg, P_t decreased from 53.3 ± 2.7 to 44.7 ± 2.0 mmHg. Plasma creatinine decreased from 2.48 ± 0.23 to 1.91 ± 0.21 mg/dl at 24 h after renal ischemia. When we raised renal artery pressure to 103 ± 7 mmHg, P_t increased to 67.2 ± 5.1 mmHg. Plasma creatinine elevated to 3.17 ± 0.14 mg·dl·24 h after renal ischemia. Changes in KIM-1, NGAL, and histology were in the similar pattern as plasma creatinine. In summary, we found that higher P_t during the ischemic phase promoted the development of AKI, while lower P_t protected from kidney injury. P_t may be a potential target for treatment of AKI.

Effect of experimental renal failure on the pharmacokinetics of losartan in rats

The purpose of this investigation was to determine whether the pharmacokinetics of the angiotensin II receptor antagonist losartan is altered in renal failure. Male Wistar rats were pretreated with uranyl nitrate or subjected to bilateral ureteral ligation to produce acute renal failure (ARF). Saline-injected and sham-operated rats, respectively, served as controls. Uranyl nitrate-treated rats showed significantly higher serum concentrations of losartan after oral administration and the area under the serum concentration-time curve (AUC(0-24)) of losartan increased about 3-fold compared to control rats. The systemic clearance of losartan significantly decreased from 410 +/- 254ml/h/kg in control to 177 +/- 112ml/h/kg in uranyl nitrate-treated rats. In order to investigate the mechanisms of reduced clearance of losartan associated with ARF, a hepatic microsome fraction was prepared from normal and ARF rats. No significant difference was found in the metabolism of losartan by hepatic microsomes prepared from ARF and control rats. In addition, the metabolic activity of microsomes was examined in the presence of uremic rat serum. The unbound clearance of losartan and the unbound clearance associated with the formation of EXP3174 in the presence of uremic serum were significantly lower than those in the presence of control serum. Furthermore, the metabolism of losartan was inhibited by indoxyl sulfate, a uremic toxin, in an uncompetitive manner. These results suggest that ARF is associated with reduced clearance of losartan due to the inhibition of hepatic metabolism by accumulated uremic toxin(s).

Melatonin attenuates acute renal failure and oxidative stress induced by mercuric chloride in rats

We evaluated the effect of melatonin (Mel), a potent scavenger of reactive oxygen species, in the course of HgCl(2)-induced acute renal failure. Rats received by gastric gavage 1 mg/kg of Mel (n = 21) or vehicle (n = 21), 30 min before the subcutaneous injection of HgCl(2) (2.5 mg/kg). Rats were killed at 24, 48, and 72 h, and plasma creatinine (S(cr)), renal histology, proliferative activity, apoptosis, and superoxide-producing cells were studied. We also determined the renal content of malondialdehyde (MDA) and glutathione (GSH) and the activities of glutathione peroxidase and catalase. Mel pretreatment (Mel plasma levels of 3.40 +/- 3.15 microgram/ml at the time of HgCl(2) injection) prevented the increment in S(cr) and reduced tubular necrosis from 41.0 +/- 10.5 to 4.2 +/- 5.1% of proximal tubules (P < 0.01). Apoptosis and postnecrotic proliferative activity were twice more intense in the group untreated with Mel. Increment in renal content of MDA and decrease in GSH resulting from HgCl(2) toxicity were prevented by Mel. Mel also induced an important reduction in superoxide-positive cells. In contrast to the beneficial effects of pretreatment with Mel, the administration of Mel in conjunction with HgCl(2) had no effect on the oxidative damage and did not prevent nephrotoxicity. We conclude that the beneficial effects of pharmacological doses of Mel are due to its antioxidant properties.

Effect of uranyl nitrate-induced renal failure on morphine disposition and antinociceptive response in rats

1. The aims of the present study were to administer morphine (14.0 mumol/kg, s.c.) to male Hooded Wistar rats and to determine the effect of uranyl nitrate-induced renal failure on: (i) the antinociceptive effect of morphine; (ii) the pharmacokinetics of morphine and morphine-3-glucuronide (M3G); and (iii) the relationship between antinociceptive effect and the pharmacokinetics of morphine in plasma and brain. 2. Renal failure was induced by a single s.c. injection of uranyl nitrate and kinetic/dynamic studies were performed 10 days after its administration, when creatinine clearance was 17% of the control group. Antinociceptive effect was measured by the tail-flick method at various times up to 2 h post-drug administration. Concentrations of morphine and M3G in plasma and brain and concentrations of creatinine in urine and serum were determined by specific HPLC methods. 3. After morphine administration, the area under the antinociceptive effect-time curve was decreased by 44% in renal failure rats. There were no differences between control and renal failure rats in: (i) plasma morphine concentration-time curves; (ii) brain morphine concentration-time curves; and (iii) plasma M3G concentration-time curves. Morphine-6-glucuronide was not detected in any plasma or brain sample from rats administered morphine and no M3G was detected in brain. 4. For both control and renal failure rats, the relationships between antinociceptive effect and plasma morphine concentration were characterized by counterclockwise hysteresis loops, probably reflecting a delay for the relatively polar morphine to cross the blood-brain barrier. The relationship between antinociceptive effect and brain morphine concentration in control rats revealed no evidence of acute tolerance and was described by a sigmoidal function. In contrast, the relationship in renal failure rats was characterized by clockwise hysteresis, which is consistent with acute tolerance development.

Effect of acute renal failure on the disposition of cefoperazone

The effect of acute renal failure on the disposition of cefoperazone was investigated. Rats, 3 days after uranyl nitrate treatment, were used to model acute renal failure. Although plasma-protein binding of cefoperazone decreased significantly in acute renal failure compared with control rats, the plasma clearance of total (bound plus unbound) drug after intravenous administration (50 mg kg(-1)) did not differ significantly between the two groups (5.61+/-2.37 mL min(-1) for control and 4.75+/-2.82 mL min(-1) for acute renal failure). Consequently the plasma clearance of the unbound drug in acute renal failure (6.14+/-1.16 mL min(-1)) was significantly lower than in control rats (15.6+/-3.7 mL min(-1), P < 0.025). Plasma clearance of the drug (both total and unbound) was also dependent on bile flow, and clearance of the unbound drug in acute renal failure rats was lower than in control rats with identical bile flow rates. To examine the mechanism of reduced unbound cefoperazone clearance, an in-vitro experiment using a simultaneous perfusion system of rat liver and kidney was performed. By changing perfusate plasma protein from bovine serum albumin to human serum albumin, the plasma clearance of the total cefoperazone changed to one-sixth in proportion to the unbound cefoperazone in the perfusate plasma. On the other hand, the plasma clearance of the total and unbound drug in acute renal failure rats decreased significantly compared with controls. These results demonstrate that the plasma clearance of unbound cefoperazone, which is mainly eliminated by the liver, decreased in acute renal failure in rats, probably due to changes in hepatic transport.

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.

Renal excretion of vancomycin in rats with acute renal failure

We have investigated the renal excretion of vancomycin in rats with acute renal failure (ARF) induced by uranyl nitrate or cisplatin. The renal clearance of the antibiotic after uranyl nitrate or cisplatin injection was separately evaluated by calculating the glomerular filtration rate (GFR) and secretory clearance. The reduced renal clearance of vancomycin in these ARF rats was a result of a decrease in both GFR and secretory clearance. The extents of the decreases in GFR and in secretory clearance were not, however, proportional, the extent of the decrease in secretory clearance being more pronounced. These results suggest that the renal tubular secretion of vancomycin was reduced more predominantly than glomerular filtration in these ARF models.

Urineless estimation of glomerular filtration rate and renal plasma flow in the rat

A simple method to perform serial renal clearance studies without urine collection in rats is described. This was applied to nonradiolabelled para-aminohippurate sodium (PAH) and iothalamate sodium (IOT) which were used respectively to estimate renal plasma flow (RPF) and glomerular filtration rate (GFR). Under isoflurane-anesthesia the jugular vein and carotid artery of Fischer 344 rats were cannulated, and a loading dose followed by a continuous infusion of PAH and IOT was administered. Steady state was reached after 30 min, and four arterial blood samples were collected over the next 30 min for analysis by HPLC (day 0). The clearances of PAH and IOT were calculated according to Fick's principle as estimates of RPF and GFR from the ratio of the infusion rates to the median solute concentrations. Three days later the femoral artery and vein were cannulated, and the same study was repeated (day 3). There was no significant difference in renal clearances of PAH and IOT between days 0 and 3. The described method gives values that compare well with others in the literature based on other methods and presents an accurate and simple way of detecting changes in renal function before and after a potentially nephrotoxic treatment regimen.

Pharmacokinetics of tinzaparin (Logiparin)--a low molecular weight heparin--after single and repeated intravenous administration in rats

After a single and repeated i.v. injections of 1 mg/kg 3H-radiolabelled tinzaparin once daily to rats for 7, 14, and 21 days, drug-related radioactivity in plasma, tissues, urine and faeces was measured by use of liquid scintillation counting. The decay in plasma could be described by a three-compartment model with half-lives of the two distributive phases and the terminal elimination phase of 15 min, 90 min, and 37 hrs, respectively. The peak plasma concentration did not change during repeated dosing, as opposed to the trough concentration which increased 3 fold. The decay in tissues was significantly different from that in plasma, and showed less fluctuations. Drug-related radioactivity accumulated gradually with repeated dosing, reaching accumulation ratios between 5 and 9, when based on trough concentrations. Slow elimination was observed from tissues, and significant amounts were still present 14 days after discontinuation of the repeated dosing. In the liver, the concentrations were almost constant during a dosing interval. After a single injection, 86% and 4% of the administered radioactive dose were excreted in urine and faeces over 7 days, respectively, the majority being recovered during the first 24 hrs, demonstrating that the major route of elimination was by renal excretion. The molecular mass distribution of radioactivity in urine was similar but not identical to the injected test substance. It was shifted slightly towards lower molecular mass and had no anti-factor Xa activity, suggesting that the heparin was either inactivated, presumably by desulphation, or that the antithrombin binding portion of the drug was cleared through a different route.

Stereoselective pharmacokinetics of atenolol in the rat: influence of aging and of renal failure

The pharmacokinetics of R- and S-atenolol after intravenous administration of racemic atenolol were studied in 3-, 12- and 24-month-old rats and in 3-month-old rats with renal failure induced by uranyl nitrate. In all age groups, the area under the plasma concentration-time curves is higher for R- than for S-atenolol; volume of distribution, total clearance and renal clearance are lower for R-atenolol than for S-atenolol, but the differences are small. In function of age there is for both enantiomers a significant increase in AUC, due, at least in part, to a decreased renal clearance; the effect of aging is not stereoselective. In rats with renal failure, the AUC of both enantiomers increases, due mainly to a decrease in renal clearance, but to a lesser degree also to a decrease in nonrenal clearance. For both enantiomers, the volume of distribution decreases and the half-life increases in the uraemic rats. The total amount of both enantiomers excreted in the urine is decreased in the rats with renal failure. There are no stereoselective effects of treatment of the rats with uranyl nitrate.

Endogenous natriuretic factors 1: sodium pump inhibition does not correlate with natriuretic or pressor activities from uremic urine

It is our purpose to isolate and characterize the putative "Natriuretic Hormone", ostensibly responsible for ECF homeostasis, as well as identify endogenous pressors and compounds that induce prolonged natriuresis; we report here our initial progress in this area. Large volumes of pooled urine collected from uremic patients were fractionated, and the resulting isolates were evaluated for in vivo natriuretic and pressor effects and Na+/K(+)-ATPase inhibitory activity in renal cells. The purification steps involved ultrafiltration to obtain materials of less than 3000 da, gel filtration, and sequential reversed-phase high performance liquid chromatography (HPLC). After each HPLC step, the fractions were evaluated for their ability to elicit significant natriuresis and/or influence mean arterial pressure in the normal conscious female rat. Each fraction was also assayed for its ability to inhibit Na+/K(+)-ATPase as determined by the inhibition of 86Rb+ uptake into MDBK renal cells. While several of the fractions elicited profound natriuresis and/or pressor activity and other fractions inhibited Na+/K(+)-ATPase, there was no correlation among the activities in individual fractions. We have concluded that this plethora of bioactivities is responsible for much of the confusion and multiplicity of crude isolates claimed to be the putative hormone. Presently we are attempting to purify each of these activities to chemical homogeneity for structure determination.

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

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

Differential effects of the degree of renal damage on p-aminohippuric acid and inulin clearances in rats

Kidney disease is generally thought to affect all segments of a nephron equally. Bricker and co-workers first proposed this as the Intact Nephron hypothesis in 1971, and evidence to date has usually supported this hypothesis. However, most supporting studies have involved severe renal failure, which may not be suitable to differentiate effects on functional sites or to test the hypothesis. The work included here examines the effects of limited renal failure on two separate functions of the nephron: glomerular filtration, as measured by inulin clearance and proximal tubular organic anion secretory function, as measured by p-aminohippuric acid (PAH) clearance. Renal failure was induced in rats by intravenous administration of uranyl nitrate, a nephrotoxin. Doses used were 0.3, 1.0, and 3.0 mg/kg rat body weight. Five days later, rats were given an intravenous infusion of PAH and inulin. Renal clearance of each compound was calculated. Results obtained in these experiments show that, at the lowest uranyl nitrate dose, PAH clearance was significantly decreased but inulin clearance was not. The ratio of CLPAH/CLIN was decreased from 2.55 in control rats to 1.21 in rats given the low dose of nephrotoxin. At higher uranyl nitrate doses, both clearance rates were significantly decreased and the ratio of CLPAH/CLIN remained close to 1.0. These results indicate that the active transport functions of the nephron can be differentiated from passive transport functions. Caution should be exercised in extrapolating renal disease changes in active renal secretion to changes in passive renal elimination and the reverse.

Glomerular hemodynamics in mercury-induced acute renal failure

As manifest by tubular collapse and the virtual absence of flow into the glomerulotubular junction (GTJ), filtration in most nephrons (SNGFR) of rats poisoned with 9 mg/kg body wt HgCl2 16 to 28 hours earlier was virtually absent. Arterial colloid osmotic pressure (COPA) and Bowman's space pressure (PBS) were modestly depressed (P less than 0.05 or below), and mean blood pressure was reduced from 115 +/- 2 mm Hg (SEM) to 97 +/- 1 mm Hg (P less than 0.001). Glomerular capillary hydraulic pressure (Pg), 25.6 +/- 1.3 mm Hg was some 24 mm Hg lower than control (P less than 0.001) and yielded a net afferent effective filtration pressure (Pnet) of 4.1 +/- 1.2 mm Hg. Excluding three rats with values greater than 10 mm Hg, Pnet averaged 2.0 +/- 0.9 mm Hg (N = 17 rats) versus 20.0 +/- 1.8 mm Hg in controls (N = 10, P less than 0.001), the former being statistically almost indistinguishable from 0 mm Hg and barely able to support any filtration. This decrease in Pg was caused by a major increase in preglomerular resistance (RA) and a reciprocal fall in efferent arteriolar resistance (RE), the RA/RE ratio of 7.2 +/- 0.8 being fourfold higher than control (P less than 0.001). Renocortical blood flow was not different from control (P greater than 0.2). A wide spread of Pg values in individual glomeruli and the absence of tubular flow despite the appearance of i.v. injected lissamine green in a quadrant of surface glomeruli suggested the possibility of a greatly increased, glomerular capillary resistance. It is concluded that reciprocal changes in RA and RE are the immediate cause of filtration failure in this form of ARF and that, in the virtual absence of filtration, tubular leakage can play no important role. Since PBS was depressed in both the developmental and established phases of ARF, tubular obstruction appears to play no direct role in the pathogenesis of this particular model of murine acute renal failure.

Non-linear tissue binding of amikacin in rats: the effect of renal impairment

Amikacin levels in serum and tissues were determined in 115 Wistar rats, 70 with normal renal function (NRF) and the remaining 45 with terminal renal impairment (TRI). The results obtained in the animals with NRF show an accumulation of the antibiotic in all the tissues studied as compared with plasma levels, specially in the renal cortex and medulla. In the rats with TRI important alterations in the plasma and tissue kinetics of the antibiotics were observed. The plasma kinetics of amikacin in rats with TRI are characterised by significant alterations in the pharmacokinetic parameters, specially those defining the distribution processes of the antibiotic. In the tissues of the latter, a significant increase in the antibiotic concentration takes place, particularly in the renal cortex. The average half-lives of the antibiotic in the tissues of rats with TRI increase compared with the group of rats with NRF, though the difference are not so significant as in the case of the plasma half-life. The use of a specific kinetic distribution model, with linear and non-linear tissue binding, showed that significant variations occur in the partition coefficient and in the Michaelis-Menten parameters, which characterize the saturable binding of Amikacin to tissue in rats with NRF and TRI.

Reduced hepatic uptake of propranolol in rats with acute renal failure

The effect of acute renal failure (ARF) on the hepatic uptake and metabolism of propranolol was investigated in relation to the hepatic clearance of the drug. ARF was induced by the subcutaneous injection of uranyl nitrate to rats. The uptake rate of propranolol in the isolated perfused liver was determined by the multiple-indicator dilution method and was found to decrease from 43.6 +/- 2.0 min-1 (mean +/- S.E.) in control to 29.4 +/- 1.7 min-1 in ARF (P less than 0.001). The recovery fraction of propranolol in effluent venous blood increased about twofold in ARF compared to control (P less than 0.05). The metabolic activity for propranolol was examined using the hepatic microsomal fraction prepared from control and ARF rats. There was no significant difference in the kinetics of oxidative metabolism of propranolol between two groups. These results suggest that the previously reported decrease in the hepatic clearance of propranolol in ARF is due to decreased hepatic uptake of the drug from the blood into the liver cells.

Methods in testing interrelationships between excretion of drugs via urine and bile

The liver and kidney are largely responsible for inactivating and eliminating drugs and other chemicals. As the excretory capabilities of the two organs overlap, a damage of one system might be compensated by the other. Because of the specificity of both renal and hepatic elimination mechanisms such an alternative excretion route is not possible generally. Several interferences are possible to characterize the relation between hepatic and renal excretion of drugs and xenobiotics. Firstly, the simultaneous assay of excreted drug amounts in urine and bile can give some information concerning the main transport routes of this drug. Thereafter the total interruption of liver or kidney function elucidates the general possibility of alternative excretion routes. But it is important for clinical practice to distinguish between different localizations of organ damages. Today some experimental possibilities exist to exclude partial functions of both kidney and liver separately. Thus it can be clarified why a compound might be excreted via liver or kidney. Moreover it can be characterized whether or not a compensation for the loss of one main excretion organ is possible or not. Such investigations are of some practical importance. Dosing guidelines for drug therapy must be completed for cases of renal or hepatic failure. Moreover the developmental pattern of both elimination routes has consequences for drug use in paediatrics as well as geriatrics. Beside this point of view such investigations are necessary for the prediction of changes in the toxicity of drugs after renal or hepatic insufficiency.

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.

The early phase of experimental acute renal failure. VI. The influence of furosemide

Experiments were performed to determine whether furosemide, given in doses high enough to induce a strong diuresis and to inhibit the mechanism of tubuloglomerular feedback, offers any protection from acute renal failure induced by a nephrotoxin or ischaemia. Microperfusion of the loop of Henle revealed that a tubular furosemide concentration of 5 x 10(-5) mol x 1(-1) was necessary to fully inhibit the tubuloglomerular feedback response to a raised sodium chloride concentration at the macula densa. The infusion of furosemide systemically to achieve such concentrations in the tubule resulted in an improvement in renal function when given before or after the nephrotoxin but was without effect when given before or after ischaemia. Measurements of furosemide concentrations in the urine, however, confirmed that sufficient amounts were applied to inhibit the feedback mechanism. It is concluded from this and similar studies that furosemide is only beneficial in models of acute renal failure with an obstructive or nephrotoxic pathogenesis, in which it acts by flushing out the noxious material and not by inhibiting the mechanism of tubuloglomerular feedback.

Comparison of vancomycin disposition in rats with normal and abnormal renal functions

Vancomycin levels in the tissues and urine of rats with renal damage were compared with those of control rats. Renal damage was induced by a single intravenous injection of uranyl nitrate. After 5 days, when the plasma urea nitrogen levels had increased 7- to 22-fold, a single intraperitoneal vancomycin injection of 10 mg/kg yielded significantly higher plasma and tissue levels in these rats than in the control rats that did not receive uranyl nitrate. At 73 h after the vancomycin injection, the plasma vancomycin concentration in the rats with renal damage was 1.8 +/- 1.1 microgram/ml (mean +/- standard deviation), whereas in control rats the level had fallen to 0.004 +/- 0.002 microgram/ml. Control rats excreted 50.5% of a single dose in the urine within the 3 days, whereas rats with renal damage excreted only 35.6%. These results indicate that vancomycin pharmacokinetics is affected by renal function in rats. Therefore, the drug should be used very cautiously in patients with impaired renal function. The serum levels must be monitored, and the frequency and size of doses may have to be reduced.

Influence of uranyl nitrate upon tubular reabsorption and glomerular filtration in blood perfused isolated dog kidneys

The early changes in tubular reabsorption, glomerular filtration, blood flow and sodium excretion brought about by uranyl nitrate were investigated in isolated, blood-perfused dog kidneys during water diuresis. No significant changes in urine volume were observed; the decrease in fluid reabsorption was counterbalanced quantitatively by a reduction in glomerular filtration rate; only a small diminution of renal blood flow was found. The balance between reabsorption and filtration was observed as well when angiotensin action or prostaglandin synthesis were inhibited. The intrarenal venous pressure rose, suggesting that an increase in proximal intratubular hydrostatic pressure caused the decrease in filtration. Tubular back-leak of fluid, or back-diffusion, induced by the toxin, were excluded. The presence of natriuretic compounds in the urine was confirmed.

Pharmacokinetics of cefoxitin administered intramuscularly to rabbits with experimentally-induced renal impairment

The pharmacokinetics of Cefoxitin were studied in rabbits with normal renal function and with varying degrees of renal impairment induced experimentally by uranyl nitrate. All animals received a single intramuscular (i.m.) dose of 40 mg kg-1 of the antibiotic. The concentrations of Cefoxitin were determined in plasma, urine, and bile by a microbiologic plate diffusion method. The antibiotic follows a two-compartment open kinetic model. In rabbits with renal impairment there is a decrease in alpha, beta, K12, K21, Ka and an increase in Vd and the (AUC)infinity zero with respect to the values obtained for rabbits with normal renal function. Linear relationships are established between log beta and log K13 and the serum creatinine. Biliary excretion of Cefoxitin is increased in states of renal impairment. A linear relationship is established between the percentage of the dose excreted in the bile and the serum creatinine.

Evaluation of methods for producing renal dysfunction in rats

The following methods for producing renal dysfunction in rats were compared: single-step 5/6th nephrectomy, two-step 5/6th nephrectomy, bilateral ureteral ligation, and uranyl nitrate injection. Control groups consisted of single- and two-step sham-operated animals and animals that received an injection of normal saline solution. The methods were evaluated on the basis of the following criteria, which were assessed daily for 6 days: survival, body weight, hematocrit, serum creatinine concentration, serum urea nitrogen concentration, serum glutamic pyruvic transaminase activity, serum albumin concentration, and serum protein binding of salicylate (determined every other day). Animals with bilateral ureteral ligation survived only 2 days, single-step 5/6th nephrectomy caused a high incidence of fatalities. Some of the methods were associated with the development of hypoalbuminemia, but no significant elevation of transaminase activity occurred. Serum protein binding of salicylate was reduced in rats with renal dysfunction. A strong positive correlation between the creatinine and urea nitrogen concentrations in the serum of animals with renal dysfunction (r = 0.91, p less than 0.001) and a negative correlation between the serum albumin concentration and salicylate free fraction (r = -0.71, p less than 0.001) were found. Uranyl nitrate injection has the advantages of technical simplicity, a high survival rate (no deaths in this study), and relatively consistent and sustained diminution of renal function (as reflected by serum creatinine and urea nitrogen concentrations).

Impaired renal blood flow autoregulation in ischemic acute renal failure

We used a model of ischemic acute renal failure featuring normal renal blood flow (RBF) to evaluate the autoregulatory capability in a preparation having a marked reduction of inulin clearance (GFR). In 10 dogs, we clamped the renal artery for 90 min (experimental); 6 dogs, 1 min only (sham). Approximately 18 hours later, we determined the autoregulatory ability from RBF responses to renal arterial constriction. GFR of the experimental dogs was 10 +/- 4 ml/min, significantly lower than GFR in the sham dogs (43 /+- 9 ml/min). RBF in the experimental dogs (189 +/- 17 ml/min) was not significantly different from that in the sham dogs (206 +/- 32). An autoregulation index, ranging from 0.49 to 1.09 (mean 0.690), was significantly larger than was that of sham dogs, which ranged from zero to 0.23 (mean 0.060). At control arterial pressures, vascular resistance was comparable in both groups; however, at reduced arterial pressures below the normal autoregulatory range, average resistance of the experimental dogs (0.62 +/- 0.12 mm Hg/[ml/min]) was significantly greater than was that of the sham dogs (0.38 +/- 0.06 mm Hg/[ml/min]). These studies indicate that a substantial loss of renal hemodynamic responsiveness follows ischemic injury to the dog even when RBF is maintained within the normal range. The loss of autoregulatory capacity associated with a severely attenuated GFR is consistent with a role for tubular flow in the normal mechanism of autoregulation.

Prostaglandin-independent protection by furosemide from oliguric ischemic renal failure in conscious rats

In 38 conscious rats divided into seven groups, acute unilateral ischemic renal failure was induced by 1 hour of complete occlusion of the left renal artery while the contralateral kidney remained intact. Renal excretory function of the left kidney was monitored up to 144 hours after ischemia and revealed a typical course of oliguric renal failure with oligoanuria persisting for more than 48 hours. Urinary osmolality and sodium concentration became plasma isotonic after release of renal artery occlusion and approximated control values on day 6 after ischemia. In nine rats, the i.v. infusion of furosemide before (6 microgram/min/100 g body wt) and after (12 microgram/min/100 g body wt) renal artery occlusion protected the ischemic kidney from oligoanuria with endogenous creatinine clearance of 0.42 +/- 0.11 ml/min/g kidney wt 5 hours after ischemia. Tubular absorption of sodium and water was at least partially preserved 36 hours after ischemia when infusion of furosemide was stopped. The loop diuretic significantly (P less than 0.01) increased total urinary prostaglandin (PG) E2 excretion before and after renal artery occlusion; and 5 hours after ischemia, PGE2 excretion from the ischemic kidney significantly exceeded that from the intact kidney (P less than 0.05). Indomethacin (1 mg/100 g body wt) administered in six animals markedly suppressed control PGE2 excretion (P less than 0.05) as well as the furosemide-induced rise in urinary PG excretion before and after ischemia but did not modify the protective effect of the diuretic in this experimental model. Inhibition of PG synthesis, however, reduced urinary flow rate and sodium and potassium excretion of the contralateral intact kidney and almost completely prevented its compensatory rise in creatinine clearance. The results indicate that mechanisms other than the intrarenal prostaglandin system must be considered to mediate the protective effects of furosemide in acute ischemic renal failure.

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.

The early phase of experimental acute renal failure. IV. The diluting ability of the short loops of Henle

Experiments were conducted to establish whether diminished solute reabsorption in the loop of Henle during acute renal failure could explain the loss of urinary concentration and participate in generating a tubuloglomerular feedback-mediated reduction in filtration rate. The electrolyte content of the fluid in the ascending limb of the loop of Henle was determined in situ by monitoring its electrical conductivity after propulsion into the distal tubule with a sudden burst perfusion. The value of the minimum electrolyte concentration decreased exponentially with increasing equilibration time, reaching a steady-state value equivalent to 27 +/- 9 mM NaCl in normal kidneys, 34 +/- 15 mM in mercuric chloride kidneys and 53 +/- 22 mM following ischaemia. A mathematical model was derived to describe the process of sodium chloride dilution from which it was possible to calculate both the permeability and transport velocity of the cortical thick ascending limb. In the normal kidney, the transport velocity was calculated to be 4.65 +/- 0.92 . 10(-5) cm/s, a value not significantly different from that of the mercuric chloride of ischaemic kidneys, and the estimated permeability was 1.13 +/- 0.52 . 10(-5) cm/s, not different from that of the mercuric chloride kidneys but significantly lower than that calculated for the ischaemic kidneys. It is concluded that for the more severely damaged ischaemic model, the loss of urinary concentrating ability was accompanied by a reduction in diluting ability of the ascending limb of the short loop of Henle, which appears to be due, at least in part, to an elevation of the passive permeability to sodium chloride in this segment.

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.