The renal lesion associated with hemoglobinemia: a study of the pathogenesis of the excretory defect in the rat

Ofloxacin Induced Hemolysis in G6PD-deficient Patient: A Rare Cause of Pigment Nephropathy

Thrombotic microangiopathy (TMA) commonly presents as a triad of acute kidney injury (AKI), jaundice, and hemolysis; however, tropical infections such as malaria, dengue, leptospira, and drugs like antimalarials can also have a similar presentation. They can cause AKI for many reasons including pre-renal causes but an important yet not relatively uncommon genetic cause of hemolytic anemia, that is, glucose 6-phosphate deficiency (G6PD) manifesting as jaundice, hemolysis, and AKI secondary to pigment nephropathy after receiving offending drugs needs to be worked up while evaluating such patients. Ofloxacin is not usually included in the lists of unsafe drugs in G6PD deficiency. Herein, we report a patient developing intravascular hemolysis secondary to G6PD deficiency associated with ofloxacin administration presenting as a rare cause for pigment nephropathy.

Hemolysis Derived Products Toxicity and Endothelium: Model of the Second Hit

Vascular diseases are multifactorial, often requiring multiple challenges, or ‘hits’, for their initiation. Intra-vascular hemolysis illustrates well the multiple-hit theory where a first event lyses red blood cells, releasing hemolysis-derived products, in particular cell-free heme which is highly toxic for the endothelium. Physiologically, hemolysis derived-products are rapidly neutralized by numerous defense systems, including haptoglobin and hemopexin which scavenge hemoglobin and heme, respectively. Likewise, cellular defense mechanisms are involved, including heme-oxygenase 1 upregulation which metabolizes heme. However, in cases of intra-vascular hemolysis, those systems are overwhelmed. Heme exerts toxic effects by acting as a damage-associated molecular pattern and promoting, together with hemoglobin, nitric oxide scavenging and ROS production. In addition, it activates the complement and the coagulation systems. Together, these processes lead to endothelial cell injury which triggers pro-thrombotic and pro-inflammatory phenotypes. Moreover, among endothelial cells, glomerular ones display a particular susceptibility explained by a weaker capacity to counteract hemolysis injury. In this review, we illustrate the ‘multiple-hit’ theory through the example of intra-vascular hemolysis, with a particular focus on cell-free heme, and we advance hypotheses explaining the glomerular susceptibility observed in hemolytic diseases. Finally, we describe therapeutic options for reducing endothelial injury in hemolytic diseases.

Recurrent acute renal failure complicating IgG warm-type autoimmune intravascular haemolysis

A 44-year-old woman experienced recurrent episodes of massive intravascular haemolysis complicated by acute oliguric renal failure over a period of 22 years. The haemolysis was induced by IgG warm type autoantibody and complement and responded to corticosteroid therapy. The renal failure was treated effectively by dialysis. To our knowledge, such a life long occurrence of recurrent intravascular haemolysis induced by IgG warm type autoantibodies together with renal failure has not been reported before.

Contribution of myoglobin-induced increases in vascular resistance to shock decompensation in experimental Crush-syndrome in anesthetized rats

Myoglobin is known to become nephrotoxic when released in greater amounts from skeletal muscle into the general circulation during shock. The present study deals with the question as to whether a myoglobin-induced increase in vascular tone additionally contributes to the detrimental role of this protein in hypovolemic shock. Anesthetized rats were subjected to 250 mg kg x h(-1) myoglobin infused i.v. during hemorrhagic hypotension of 50 mmHg. Shock survival time was measured, as were blood flow and vascular resistance in kidney, intestine, brain, and heart, using the microsphere method. Rats subjected to only myoglobin or hemorrhage survived a period of >120 min; in contrast, rats, exposed to both myoglobin and hemorrhage died at 68 +/- 9 min. When the animals subjected to only hemorrhage and to myoglobin/ hemorrhage were compared, significantly lower values were found in the latter group with respect to blood flow in the kidney (1.7 +/- 0.1 vs. 0.2 +/- 0.05 ml x min(-1) x g(-1)), small intestine (1.0 +/- 0.1 vs. 0.5 +/- 0.1 ml x min(-1) x g(-1)), cardiac output (112 +/- 5 vs. 62 +/- 10 ml(-1) x min(-1) x kg(-1)), and significantly higher values of total peripheral vascular resistance (0.45 +/- 0.02 vs. 0.81 +/- 0.12 mmHg x min x ml(-1) x kg) at 50 min of hypotension. It is assumed that these effects of myoglobin are induced by its ability to scavenge endogenous nitric oxide, because a modified, non-nitrosylable myoglobin was unable to induce such effects. The results support the view that a pathological release of myoglobin into the general circulation causes increases in vascular resistance of vital organs that may contribute to decompensation of tissue supply when occurring in hypovolemic shock.

Human red blood cell hemolysate is a potent mitogen for renal tubular epithelial cells

Conditions associated with intravascular hemolysis are often complicated by acute renal failure which is characterized by renal vasoconstriction and tubular injury. However, the effects of human red blood cell (RBC) hemolysate on renal tubular epithelial cell function have not been well characterized. We therefore measured the effect of distilled water-lysed human RBCs on cultured LLC-PK1 cell function. We found that human RBC hemolysate produced a marked effect to promote LLC-PK1 3H-thymidine uptake that was several-fold higher than that produced by maximal concentrations of several known growth factors. Partial purification of human RBC hemolysate by sequential centrifugation and passage over a column that removes low molecular weight substances each significantly reduced, but did not totally eliminate, the effect of human RBC hemolysate to promote 3H-thymidine uptake. Exposure of LLC-PK1 cells to horse myoglobin also stimulated 3H-thymidine incorporation in LLC-PK1 cells. A reducing agent (ascorbic acid) decreased the effect of horse myoglobin and of human RBC hemolysate to promote LLC-PK1 mitogenesis. Ascorbic acid also decreased the methemoglobin content of human RBC hemolysate. The effect of human RBC hemolysate to increase LLC-PK1 incorporation of 3H-thymidine could also be significantly decreased by either of two inhibitors of tyrosine kinase. These results suggest that there are several components of human RBC hemolysate that promote LLC-PK1 3H-thymidine incorporation. One of these components appears to be methemoglobin that exerts its effect via a tyrosine kinase signal transduction pathway.

The physiological and histopathological response of dogs to exchange transfusion with polyethylene glycol-modified bovine hemoglobin (PEG-Hb)

The performance of polyethylene glycol-modified bovine hemoglobin (PEG-Hb) was evaluated in dogs following the replacement of 30% or 50% of their blood volume with PEG-Hb or lactated Ringer's solution (LRS). Dogs fully instrumented with catheters and blood pressure probes were transfused by simultaneous bleeding from the jugular vein and infusion of PEG-Hb or LRS via the cephalic vein. Animals were monitored for abnormal behavior and clinical signs for fourteen days. No mortalities, overt toxicity, changes in body weight, food consumption or ophthalmology, or discernable trends in hematology, blood chemistry coagulation, urinalysis or hemodynamic parameters that could be attributed to PEG-Hb were noted. Blood gas analyses were steady and within physiological ranges. Dose-related histopathological findings of vacuolated histiocytes in the femoral bone marrow, splenic parenchyma, the medulla of the mesenteric and mandibular lymph nodes, and vacuolated sinusoidal cells in the liver and the renal tubular epithelial cells were believed to be related to the phagocytosis and degradation of PEG-Hb by the reticulo-endothelial system. The maintenance of high oxygen levels in the circulation for the two-week treatment period, as well as the insignificant physiological and histopathological findings indicate that PEG-Hb could be a successful blood substitute.

Blood substitutes: oxygen-carrying acellular fluids

Blood substitutes are acellular fluids that can transport and deliver oxygen to the tissues. The blood substitutes most likely to be available and effective for veterinary use are the hemoglobin-based oxygen carriers (HBOCs) containing modified human, mammalian, or recombinant hemoglobin. HBOCs can be stored at room temperature and do not require typing or crossmatching. Chemical modifications of hemoglobin affect its physiologic and pharmacologic properties and facilitate oxygen transport. Although many of the metabolic and toxicologic consequences of HBOC infusion are not fully understood, an approved product will likely be available in the near future.

Inorganic iron effects on in vitro hypoxic proximal renal tubular cell injury

Iron-dependent free radical reactions and renal ischemia are believed to be critical mediators of myohemoglobinuric acute renal failure. Thus, this study assessed whether catalytic iron exacerbates O2 deprivation-induced proximal tubular injury, thereby providing an insight into this form of renal failure. Isolated rat proximal tubular segments (PTS) were subjected to either hypoxia/reoxygenation (H/R: 27:15 min), "chemical anoxia" (antimycin A; 7.5 microM x 45 min), or continuous oxygenated incubation +/- ferrous (Fe2+) or ferric (Fe3+) iron addition. Cell injury (% lactic dehydrogenase [LDH] release), lipid peroxidation (malondialdehyde, [MDA]), and ATP depletion were assessed. Under oxygenated conditions, Fe2+ and Fe3+ each raised MDA (approximately 7-10x) and decreased ATP (approximately 25%). Fe2+, but not Fe3+, caused LDH release (31 +/- 2%). During hypoxia, Fe2+ and Fe3+ worsened ATP depletion; however, each decreased LDH release (approximately 31 to approximately 22%; P < 0.01). Fe(2+)-mediated protection was negated during reoxygenation because Fe2+ exerted its intrinsic cytotoxic effect (LDH release: Fe2+ alone, 31 +/- 2%; H/R 36 +/- 2%; H/R + Fe2+, 41 +/- 2%). However, Fe(3+)-mediated protection persisted throughout reoxygenation because it induced no direct cytotoxicity (H/R, 39 +/- 2%; H/R + Fe3+, 25 +/- 2%; P < 0.002). Fe3+ also decreased antimycin toxicity (41 +/- 4 vs. 25 +/- 3%; P < 0.001) despite inducing marked lipid peroxidation and without affecting ATP. These results indicate that catalytic iron can mitigate, rather than exacerbate, O2 deprivation/reoxygenation PTS injury.

Myoglobin depletes renal adenine nucleotide pools in the presence and absence of shock

To assess whether myoglobin adversely affects renal adenylate pools, rats were infused with purified myoglobin (50 mg/100 g body wt) for two hours and renal ATP, ADP, and AMP levels were measured in the absence of shock, after 25 minutes of hemorrhagic shock (55 to 60 mm Hg) or 30 minutes post-recovery. In the absence of shock, myoglobin lowered ATP by 24% (assessed 65 min post-infusion) without affecting renal blood flow (RBF). This effect was completely blocked by deferoxamine (DFO) treatment and it could not be reproduced by ribonuclease infusion (a non-Fe containing, but filtered, protein). Myoglobin + shock caused a three- to fourfold greater decline in ATP than did shock alone despite comparable RBFs. Shock plus myoglobin, but neither one alone, induced substantial S1/S2 proximal tubular morphologic damage and a severe reduction in creatinine clearance, confirming synergistic injury. Ribonuclease completely reproduced myoglobin's effect on shock-induced adenylate profiles. DFO +/- hydroxyl radical scavenger therapy (Na benzoate) did not block the myoglobin shock effect on adenylate pools. Post-shock adenylate recovery was not compromised by myoglobin pre-treatment. If renal artery occlusion (RAO), rather than shock, was used as the ischemic challenge, myoglobin had no discernible impact on adenine nucleotide content. This study concludes that: 1) myoglobin modestly lowers baseline adenylate pools due to an Fe dependent mechanism; 2) myoglobin drastically accentuates shock-induced adenylate depletion by a non-hemodynamic/non-Fe dependent mechanism; 3) myoglobin nephrotoxicity cannot be attributed solely to tissue iron loading; and 4) the RAO model can completely mask important influences on ischemic cellular energetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Drug-induced haemolysis and renal failure in children with glucose-6-phosphate dehydrogenase deficiency in Afghanistan

Twenty children (18 boys and 2 girls) with a proven or presumptive diagnosis of glucose-6-phosphate dehydrogenase (G-6-PD) deficiency developed intravascular haemolysis following administration of antimalarials in 9, chloroquine and chloramphenicol in 1, chloroquine, chloramphenicol and aspirin in 1, chloramphenicol and aspirin in 3, and aspirin alone in 4. Eleven of these children developed acute renal insufficiency. All were managed with supportive care, including blood transfusion, forced diuresis and peritoneal dialysis wherever indicated. Only 16 children recovered completely. The occurrence of G-6-PD deficiency is being reported for the first time in Afghanistan.

The effect of substance(s) associated with malarial parasites on C3b inactivator

The effects of a substance or substances associated with malarial parasites on the inhibitory role of C3b inactivator in immune adherence were investigated. The test system involved adherence of immune complexes of complement-bearing sheep erythrocytes and rabbit antibody, using human group O erythrocytes and human renal glomerular tissues as indicators. Malarial antigen and other soluble by-products of the malarial parasites, presumably present in spent culture medium, did not interfere with the inhibitory role of C3b inactivator. However, malarial pigment, both crude and purified, enhanced immune adherence in the presence of C3b inactivator. It is suggested that malarial pigment, by inhibiting the action of C3b inactivator, may play a significant role in the immunopathogenesis of renal lesions associated with malarial infections.

Pathophysiology of the kidney in rats with Heymann nephritis

Alterations in kidney function were assessed early in the course of Heymann nephritis that was induced in rats by immunization with Fx1A, an extract prepared from rat kidney cortex. Whole kidney and single nephron function were evaluated by clearance and micropuncture techniques. Kidney function was studied in stage 1 of Heymann nephritis, before the onset of proteinuria, and in stage 2, when antibodies are deposited along the brush border of proximal tubules. Although overall kidney function was similar in rats in stage 1 and normal controls, glucose reabsorption was somewhat depressed in the first part of the proximal convoluted tubule in stage 1. Both whole kidney and single nephron glomerular filtration rates were depressed in stage 2. Proteinuria in stage 2 was characterized by an increased albumin sieving coefficient, which resulted in an elevated excretion of albumin. Furthermore, several proximal tubule functions (glucose and fluid reabsorption and PAH extraction) were substantially depressed in stage 2. These findings demonstrate that immunological injury to the proximal tubules in stage 2 of Heymann nephritis produces a significant impairment of proximal function.

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.

Glomerular mesangial and endothelial cell swelling following temporary renal ischemia and its role in the no-reflow phenomenon

The purpose of these experiments was to define changes in glomeruli of rats kidneys which could account for a marked reduction of blood flow immediately following temporary ischemia. After the renal artery had been clamped for 60 minutes, mesangial and endothelial cellular swelling was sufficiently severe to compress and trap intracapillary erythrocytes, obstruct capillary lumens, and prevent reflow of an isotonic carbon suspension. Perfusion of saline solution before the renal arteries were clamped washed blood from the kidney, and the resulting cellular swelling alone was not sufficient to block capillary lumens. Erythrocyte trapping did not occur after 15 minutes of ischemia. Swelling of glomerular and tubular epithelial cells produced some extrinsic capillary compression that could contribute to erythrocyte trapping, but this appeared to be of minor importance in producing the no-reflow phenomenon.

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.

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.

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.

Renal cortical blood flow in glycerol-induced acute renal failure in the rat

Renal hemodynamics and renal function were evaluated in rats at 3, 24, and 48 hours and at 7 days after the induction of acute renal failure (ARF) by glycerol injection. Three hours after induction of ARF, creatinine clearance was 0.04 ml/min/100 g; renal blood flow (RBF), 1.99 ml/min/100 g; and filtration fraction, 3.7%. All were abnormally low. Although the administration of isotonic saline (total dose, 3% of body weight) to rats 3 hours after glycerol injection significantly improved creatinine clearance (0.17 ml/min/100 g), RBF (2.54 ml/min/100 g), and filtration fraction (12.9%), these values still were significantly lower than those of controls (creatinine clearance = 0.50 ml. ml/min/100 g, RBF = 4.92 ml/min/100 g, filtration fraction = 20.0%, all P values less than 0.001). Serum creatinine concentrations were significantly elevated at 24 hours (3.72% gm/100 ml), 48 hours (4.69 mg/100 ml), and 7 days (0.66 mg/100 ml) after glycerol injection compared to control (0.46 mg/100 ml, all P less than 0.01). RBF during these phases was not different from normal (4.41 ml/min/100 g). RBF 3 hours after bilateral ureteral obstruction was measured to determine the effects of tubular obstruction on renal hemodynamics. The RBF of rats with ureteral obstruction (4.12 ml/min/100 g) was not significantly different from controls (4.41 ml/min/100 g), suggesting that tubular obstruction in this model of ARF is probably not the cause of decreased RBF. The depressed glomerular filtration, as reflected by the decreased creatinine clearance that occurs during glycerol-induced ARF, is probably related to altered intrarenal vascular resistance or to changes in glomerular capillary permeability, or both.

Acute renal failure: an important complication of cardiac surgery in infants

Acute renal failure occurred in association with cardiac surgery in 20 of 248 infants (8%). Hypotension, poor tissue perfusion, and hypoglycemia were the most important factors recognized in the pathogenesis and outcome of the ARF. However, many infants were extremely ill preoperatively. The most frequent operative procedures performed in the 20 patients were open-heart surgery with total correction under deep hypothermia and repair of coarctation of the aorta. Thirteen of the 20 infants with ARF died. The combination of a major operative procedure, cardiac failure, hypoglycemia, hypotension, and compromised renal function imposes important constraints in the treatment of hyperkalemia, hypoglycemia, correction of acid-base distrubances, and the administration of fluids.

Role of prostaglandins in the pathogenesis of acute renal failure

It is suggested that impaired glomerular infiltration in acute renal failure may be due, if only in part, to the derangement of a normal local feedback mechanism involving prostaglandins. According to this hypothesis, prostaglandins made in the medulla normally enter the loop of Henle and thus are present in distal tubule fluid reaching the macula densa. In the absence of direct vascular channels connecting the renal medulla with the outer cortex, this may be the only route by which medullary prostaglandins can reach the cortex without being destroyed by dehydrogenases. Under most circumstances in which renal perfusion and glomerular filtration fall, flow through Henle's loop continues, albeit at a reduced rate. This slowed flow through the loop and augmented prostaglandin release combine to produce a high concentration of prostaglandin in fluid leaving the medulla which, acting on the macula densa, counteracts the vasoconstrictor stimulus. If, however, filtration stops completely because of overwhelming vasoconstriction, flow along the loop also stops ans prostaglandins no longer reach the macula densa. Thus, the prostaglandin feedback loop would be opened, constrictor mechanism remain unchecked, and filtration failure perpetuated. It is proposed that such a self-perpetuating mechanism might operate in acute renal failure.

Studies of the mechanism of oliguria in a model of unilateral acute renal failure

To further evaluate the mechanism of the oliguria of acute renal failure, a model was utilized in which intense and prolonged vasoconstriction produced the unilateral cessation of urine flow. The radioactive microsphere method was used to measure total and regional blood flow before and after the intrarenal infusion of norepinephrine, 0.75 mug/kg/min, for 2 h in the dog. In the control kidney, renal blood flow increased 32% 48 h after norepinephrine in association with a fall in the fractional distribution of flow to the outer cortex. In the experimental kidney, total renal blood flow fell from 190 ml/min before norepinephrine to 116 ml/min at 48 h (P < 0.025) with a uniform reduction in cortical blood flow. After the administration of 10% body wt Ringer's solution, there was a marked redistribution of flow to inner cortical nephrons in both the control and experimental kidney. In addition, there was a marked increase in total blood flow in both kidneys. On the experimental side, flow rose to 235 ml/min, a value greater than in either the control period (P < 0.05) or at 48 h after norepinephrine (P < 0.001). However, in spite of this marked increase in blood flow, there was essentially no urine flow from the experimental kidney. In separate studies, the animals were prepared for micropuncture. In all studies, the surface tubules were collapsed, and there was no evidence of tubular obstruction or leakage of filtrate. Over 99% of the 15-muM spheres were extracted in one pass through the experimental kidney. An analysis of the forces affecting filtration suggested that an alteration in the ultrafiltration coefficient may be responsible, at least in part, for the anuria in this model. In this regard, transmission and scanning electron microscopy revealed a marked abnormality in the epithelial structure of the glomerulus. It is suggested that a decrease in glomerular capillary permeability may be present in this model of acute renal failure.

The renal functional defect of postobstructive nephyropathy. The effects of bilateral ureteral obstruction in the rat

This study was designed to examine the pathogenesis of the excretory defect produced by bilateral ureteral obstruction in the rat. After release of obstruction of 24 hr duration glomerular filtration rate was reduced to 20% of normal. Free flow proximal tubular pressure was normal, excluding residual obstruction as a cause of depressed filtration, and indicating that an intrarenal hemodynamic abnormality was primarily responsible for the excretory defect. Total renal blood flow and cortical distribution of flow were normal. Clearance and micropuncture studies indicated the presence of marked heterogeneity of nephron function with residual excretory function residing primarily in vasodilated nephrons in which decreased postglomerular arteriolar resistance effected a reduction in glomerular filtration pressure. Heterogeneity of nephron function was evidenced by a wide scatter of values for single nephron filtration rate and from direct intratubular injection of dye which revealed that at least 28% of surface nephrons were either nonfiltering or had filtration rates too low to measure. The observed decrease in Hippuran extraction and increased ratio of Hippuran to inulin clearance ratio is characteristic of the vasodilated kidney. Further evidence of the vasodilated nature of residual functioning nephrons was demonstrated by the failure of intrarenal papaverine infusion to increase filtration rate in this lesion. The hemodynamic defect produced by bilateral obstruction is contrasted with that seen after release of unilateral ureteral ligation in which depression of filtration rate appears to result primarily from preglomerular vasoconstriction. This difference raises the possibility that a vasodilating substance accumulates during total suppression of renal excretory function. Diuresis and natriuresis were constant features of the postobstructive lesion. The present data support previously published studies which localize the defect in sodium transport to the distal nephron and indicate that this defect is a consequence of increased intraluminal pressure and tubular dilatation induced by bilateral ureteral ligation.

Renal handling of phosphorus in oliguric and nonoliguric mercury-induced acute renal failure in rats

The renal handling of phosphorus was evaluated in rats with acute renal failure (ARF) induced by injection of mercuric chloride (HgCl(2)). Clearances of endogenous creatinine (Ccr) and of phosphorus (Cp) were measured in the following groups: 1. Intact animals (control); 2. Parathyroidectomized rats (PTX) with normal kidney function (PTX control); 3. Animals with mercury-induced acute renal failure (Hg-ARF); 4. PTX rats with Hg-ARF; 5. Rats with Hg-ARF maintained normophosphatemic with dietary phosphate restriction; 6. Animals with oliguric ARF following renal artery constriction; 7. Rats with unilateral Hg-ARF. In addition, radioinulin clearances were measured in 6 normal and in 14 azotemic animals and correlated with simultaneously recorded endogenous Ccr. Radioinulin clearance was also used as an estimate of GFR (glomerular filtration rate) in the animals of group 7. The Cp/GFR in the intact animals (group 1) was 0.25 +/-0.06 (mean +/-SD). PTX (group 2) caused a subsequent decrease in Cp/GFR to 0.11 +/-0.04 P < 0.0005. The ARF animals in group 3 were classified either as oliguric (U(vol) [urine volume] <2 ml/24 hr, Ccr 0.008 +/-0.005 ml/min) or nonoliguric (V(vol) >2 ml/24 hr, Ccr 0.136 +/-0.12). The Cp/GFR in the oliguric animals (0.16 +/-0.09) was lower than that in group 1, P < 0.0005, and failed to increase following administration of exogenous parathyroid hormone. The Cp/GFR in the oliguric animals in groups 5 and 7 was also lower than the clearance ratio in group 1, 0.030 +/-0.08 and 0.077 +/-0.006, respectively. In the nonoliguric ARF animals of group 3 the Cp/GFR (0.94 +/-0.29) was higher than that in group 1, P < 0.0005. In the nonoliguric ARF animals of group 4 the Cp/GFR 0.27 +/-0.08 did not differ from the clearance ratio in group 1, however it was higher than that in the PTX animals (group 2) P < 0.0005. Cp/GFR in the nonoliguric animals of group 5 was not different from that in the nonoliguric rats of group 3. In the animals with nonoliguric unilateral Hg-ARF Cp/GFR on the affected side 0.51 +/-0.16 was higher than that on the control (contralateral) side, 0.23 +/-0.07, P < 0.0005. These results indicate that the low Cp/GFR observed in the oliguric ARF animals was not related to the level of circulating parathyroid hormone nor to the presence or absence of azotemia but probably was due to a reduced renal cortical perfusion. The high Cp/GFR in the nonoliguric ARF animals could be explained by secondary hyperparathyroidism and impaired phosphorus reabsorption due to tubular injury.

Inducible heme oxygenase in the kidney: a model for the homeostatic control of hemoglobin catabolism

We have recently identified and characterized NADPH-dependent microsomal heme oxygenase as the major enzymatic mechanism for the conversion of hemoglobin-heme to bilirubin-IXalpha in vivo. Enzyme activity is highest in tissues normally involved in red cell breakdown, that is, spleen, liver, and bone marrow, but it usually is negligible in the kidney. However, renal heme oxygenase activity may be transiently increased 30- to 100-fold following hemoglobinemia that exceeded the plasma haptoglobin-binding capacity and consequently resulted in hemoglobinuria. Maximal stimulation of enzyme activity in rats is reached 6-16 hr following a single intravenous injection of 30 mg of hemoglobin per 100 g body weight; activity returns to basal levels after about 48 hr. At peak level, total enzyme activity in the kidneys exceeds that of the spleen or liver. Cyclohexamide, puromycin, or actinomycin D, given just before, or within a few hours after, a single intravenous injection of hemoglobin minimizes or prevents the rise in renal enzyme activity; this suggests that the increase in enzyme activity is dependent on continued synthesis of ribonucleic acid and protein. The apparent biological half-life of renal heme oxygenase is about 6 hr. These observations indicate that functional adaptation of renal heme oxygenase activity reflects enzyme induction either directly or indirectly by the substrate, hemoglobin. Filtered rather than plasma hemoglobin appears to regulate renal heme oxygenase activity. Thus, stabilization of plasma hemoglobin in its tetrameric form with bis (N-maleimidomethyl) ether, which diminishes its glomerular filtration and retards it plasma clearance, results in reduced enzyme stimulation in the kidney, but enhances its activity in the liver. These findings suggest that the enzyme is localized in the tubular epithelial cells rather than in the glomeruli and is activated by luminal hemoglobin. Direct support for this concept was obtained by the demonstration of heme oxygenase activity in renal tubules isolated from rabbits that had been injected with hemoglobin.

Evaluation of the renal toxicity of heme proteins and their derivatives: a role in the genesis of acute tubule necrosis

This investigation studies the toxicity of heme proteins and/or their break-down products on renal function. Heme proteinemia precedes acute tubule necrosis at a frequency great enough to suggest a causal relationship between the two events. Physiological and metabolic functions of kidney slices are investigated in several models of acute tubule necrosis. Organic acid and organic base transport is depressed earliest. These alterations in tubule function cannot be explained by ischemia or obstruction alone. Heme proteinemia in rats or incubation of renal slices in medium containing heme proteins yields several interesting observations. Neither in vivo or in vitro do hemoglobin and methemoglobin alone produce a depressive effect on the transport systems studied. However, parallel to many clinical situations, when such secondary insults as hypoxia and elevated ammonia concentrations are included in the experimental design, transport functions are depressed. Ferrihemate, a molecule smaller than hemoglobin or methemoglobin, depresses transport function without secondary insults. From these studies it is concluded that heme proteins play a role in tubule dysfunction seen in acute tubule necrosis. A model is presented that collates these data with other factors known to play a part in the pathogenesis of this renal syndrome.

Renin and acute renal failure: studies in man

Plasma renin concentration was increased, usually appreciably, in 22 out of 25 patients with acute renal failure, the average value being 226 units/litre (mean for normal subjects 8.2 units/1.). The highest renin values were found in the first 10 days of the disease; lower and sometimes normal values were found subsequently. Unequivocal acute tubular necrosis was present in only two of the eight cases examined post mortem.These findings are compatible with Goormaghtigh's proposal that an excess of renin and angiotensin may act within the kidney to produce acute renal failure.