Membrane attack complex deposition in experimental glomerular injury.

The complement (C) system is an important mediator of glomerular injury both through its attraction of inflammatory cells and by a cell-independent effect on glomerular capillary wall permeability. We have postulated that the latter effect may be mediated by the terminal components of the C system, the membrane attack complex (MAC). We examined several models of immunologic renal injury in the rat by immunofluorescence for the presence of neoantigens of the MAC. Rats with experimental membranous nephropathy induced by antibody binding to a fixed glomerular antigen (passive Heymann nephritis, PHN) or a planted antigen (autologous phase of PHN) had moderate proteinuria and 1-2+ capillary wall deposits of IgG, rat C3, and MAC. C depletion with cobra venom factor (CVF) significantly decreased proteinuria and prevented deposition of C3 and MAC. Rats with active Heymann nephritis had similar capillary wall deposits of MAC. Rats with anti-glomerular basement membrane nephritis developed severe proteinuria which was not affected by CVF treatment and had no glomerular deposits of MAC. Rats with nonimmunologic proteinuria induced by aminonucleoside of puromycin also had no glomerular deposits of MAC. In rats unilaterally nephrectomized before the induction of PHN segmental glomerular sclerosis developed after 6 months with deposits of MAC in the sclerotic areas. The presence or absence of glomerular deposits of MAC in experimental renal disease correlates well with the pathogenetic role of C in the production of injury. These results support a role for the MAC in the mediation of several types of glomerular injury.     

Angiotensin-converting enzyme inhibition prevents loss of glomerular hydraulic permeability in passive heymann nephritis

We used morphometric techniques and theoretical analysis to investigate structural and functional changes of the glomerular membrane that develop in passive Heymann nephritis (PHN), an experimental model of human membranous glomerulopathy The effect of angiotensin-converting enzyme (ACE) inhibition on the above parameters was also investigated to explore the mechanisms by which this treatment exerts functional and structural protection at the renal tissue level. Morphometric analysis of glomerular capillary by light and electron microscopy was performed in normal control rats and in rats injected with rabbit anti-Fx 1A antibody, 12 months after induction of PHN. A group of PHN rats treated with lisinopril during the observation period was also investigated. Glomerular capillary architecture was not significantly altered in PHN rats, thus glomerular volume and capillary lumen volume were comparable with normal controls; only mesangial volume was significantly elevated in PHN rats. Glomerular membrane structure was significantly affected by PHN: the thickness of the glomerular basement membrane (GBM) increased, and the frequency of epithelial filtration slits decreased. Electron-dense deposits in the subepithelial space of the GBM were estimated to occupy more than 20% of the GBM area. Theoretical analysis of glomerular hydraulic permeability allowed us to predict that, after these structural changes, the permeability of the GBM and the epithelial layer significantly decreased, with an average reduction in the ultrafiltration coefficient (Kf) of approximately 43%. ACE inhibition limited mesangial expansion and prevented changes of glomerular epithelial cells (filtration slit frequency) but not GBM thickening. Immune deposits within the GBM were only partially prevented by lisinopril. A selective effect on epithelial permeability was calculated in lisinopril-treated rats, and a partial preservation of Kf reduction was observed. These results suggest that structural changes of the GBM and epithelial cells that develop in PHN are responsible for the reduced filtration capacity observed in this model. ACE inhibition only partially prevented immune-deposits in the GBM and favorably affected epithelial cell structure. These selective effects on glomerular podocytes may contribute to preserve water and macromolecule permeability of the glomerular capillary wall in this immunologic model of kidney disease.     

Determinants of glomerular localization of subepithelial immune deposits: effects of altered antigen to antibody ratio, steroids, vasoactive amine antagonists, and aminonucleoside of puromycin on passive Heymann nephritis in rats.

The role of circulating immune complex deposition versus in situ complex formation in membranous nephropathy is controversial. Passive Heymann nephritis in rats resembles membranous nephropathy in man and was induced by injection of sheep antibody to rat proximal tubular epithelial cell brush border antigen (anti-Fx1A). Minutes after injection of 1 ml. of anti-Fx1A, subepithelial immune deposits were seen by immunofluorescence and electron microscopy, and proteinuria appeared within 5 days. The effects of alterations in the dose of administered antibody, corticosteroid therapy, and vasoactive amine blockade on the development of subepithelial deposits and consequent proteinura were studied. Variation of the dose of anti-Fx1A from 0.25 ml. to 1 ml. resulted in a progressive increase in the size and number of glomerular capillary wall deposits, but no alterations in their distribution. Only those rats which received 1 ml. became proteinuric within 5 days. Corticosteroid therapy and vasoactive amine blockade, begun 24 hours prior to the induction of passive Heymann nephritis and continued until termination of the study 5 days later, had no effect on the amount or site of immune complex formation, nor on the extent of proteinuria as compared to untreated controls. In contrast, in rats with unilateral proteinuria produced by the selective perfusion of one kidney with aminonucleoside of puromycin 7 days prior to the induction of passive Heymann nephritis, there was a marked reduction of subepithelial deposits in the perfused kidney as compared to the nonperfused contralateral kidney. In this model of membranous nephropathy, systemic factors play little role in the development of subepithelial deposits, whereas local factors are critical. These findings are consistent with the hypothesis that subepithelial immune deposits form locally.     

Dynamics of glomerular ultrafiltration in Amphiuma means

To study renal function inAmphiuma means, the hydrostatic pressures in vascular and tubular structures and the glomerular filtration rate were determined at different arterial blood pressures. In the arterial blood pressure range studied no evidence of autoregulation of the glomerular capillary pressure or of the hydrostatic pressure gradient over the capillary membrane was found. The glomerular filtration ceases at an arterial blood pressure below 12 cm H₂O. No significant difference between tubular free flow pressure and peritubular capillary pressure was noted. Furthermore, it was found that the glomerular capillary pressure could be estimated by measuring the intratubular stop-flow pressure and arterial colloid osmotic pressure at an arterial pressure above 15 cm H₂O. It was also found possible to measure the glomerular capillary pressure at the very end of the afferent arteriole. The protein concentrations in afferent and efferent arteriolar blood were determined and the colloid osmotic pressures were calculated according to a new formula derived forAmphiuma plasma. The dynamics of glomerular ultrafiltration was evaluated. A filtration equilibrium across the glomerular membrane was reached, since the efferent colloid osmotic pressure was not significantly different from the hydrostatic pressure gradient across the glomerular capillary membrane.     

Pathophysiologic glomerulotubular growth factor link

Circumstantial evidence from clinical and pathologic correlations in patients with glomerular diseases and proteinuria suggest that glomerular protein ultrafiltration contributes to tubulointerstitial injury. A series of studies was performed to examine the hypothesis that in rats with adriamycin-induced nephropathy or with diabetic nephropathy (but not in normal rats) high molecular wt. growth factors are ultrafiltered into tubular fluid and act on tubular cells through apical membrane receptors. Analysis of proximal tubular fluid that was collected by nephron micropuncture indicates ultrafiltration of IGF-I, TGF-beta and HGF. Respective receptors are also expressed in apical membranes in some parts of the nephron as examined by immunohistochemistry. In vitro cell culture experiments using proximal tubular fluid obtained from rats with experimental glomerular diseases indicate that ultrafiltered IGF-I may contribute to increased distal tubular Na-absorption. Indirect evidence also suggests that this growth factor may increase the secretion of collagen types I and IV in proximal tubular cells. TGF-beta and HGF cause increased expression and basolateral secretion of MCP-1 in proximal tubular and collecting duct cells. There may be other biologic effects on tubules that are caused by apical exposure to ultrafiltered growth factors. These studies suggest that the glomerular ultrafiltration of bioactive proteins causes or contributes to tubulo-interstitial pathology in glomerular proteinuria.     

Sequence of events in the glomerular capillary wall at the onset of proteinuria in passive Heymann nephritis

Proteinuria in passive Heymann nephritis (PHN) results from complement-mediated glomerular injury, since complement depletion with cobra venom factor (CVF) prevents proteinuria. However, there are no comprehensive morphological studies identifying the sites of injury leading to onset of proteinuria. To address this issue, we attempted to locate sites of injury involved in the onset of proteinuria in PHN. PHN was induced in intact Munich-Wistar rats (PHN-rats, examined at days 3, 5, and 7) and in complement-depleted rats (CVF treated, PHN-CVF-rats, examined at days 3 and 5). The distribution of endogenous albumin in the glomerular basement membrane (GBM) was studied in in situ drip-fixed glomeruli using immunogold immunocytochemistry, and glomerular anionic sites were visualized by polyethyleneimine staining. In addition, the ultrastructural localization of an epitope recognized by a proteinuria-inducing monoclonal antibody (called 5-1-6) directed against the slit diaphragm was examined. Significant proteinuria was seen in intact PHN-rats, starting at day 5. The intensity of gold labeling for endogenous albumin was significantly increased at the outermost site of the GBM (GBM interfacing foot process and the filtration slit, designated area O) at day 3 in both PHN-rats and PHN-CVF-rats in comparison to untreated controls. At day 5, labeling for albumin in area O was decreased in PHN-rats, but not in PHN-CVF-rats, where it was then higher; in PHN-rats, some areas between epithelial cells and subepithelial deposits were almost free of albumin labeling at day 7. There was no evidence of epithelial cell detachment in any group at day 5, but on day 7 limited focal detachment was seen exclusively in PHN-rats. In proteinuric rats, amorphous material that stained for albumin could be seen in the urinary space, without any exocytosis of labeling by glomerular epithelial cells. A significant reduction of intensity of staining for anionic sites was seen in parallel in both groups, but only in the regions of the lamina rara externa adjacent to subepithelial deposits. This local loss of charge might contribute to enhanced permeability to albumin in both PHN- and PHN-CVF-rats. Changes in the appearance of the filtration slits and in the density and distribution of antigen recognised by monoclonal antibody 5-1-6 were similar in PHN- and PHN-CVF-rats at day 5. Complement depletion prevented neither the reduction in anionic sites of the GBM nor the changes in the slit diaphragm observed. These data suggest that albumin leakage between the epithelial cell and the GBM (area O) could occur in PHN-rats, perhaps as a result of epithelial foot-process changes. This may be the final link in the chain of events responsible for the onset of proteinuria in PHN.     

Prognostic significance of glomerular and tubulointerstitial morphometry in idiopathic membranous nephropathy

The purpose of our study was to investigate the prognostic value of clinical and pathological, in particular glomerular and tubulointerstitial morphometric variables in idiopathic membranous nephropathy (IMN). We prospectively followed 60 Caucasian patients diagnosed with idiopathic membranous nephropathy for at least 2 years or until primary outcome (≥50% permanent decrease in estimated glomerular filtration rate or death). Glomerular and tubulointerstitial morphometric variables at the time of renal biopsy were analyzed with respect to this outcome. Univariate analysis revealed that significant negative prognostic factors for this outcome were higher cholesterol and smaller albumin concentrations, higher creatinine and maximal 24-h proteinuria, higher grade of nephroangiosclerosis, higher glomerular basement membrane thickness and glomerulopathy index, higher interstitial fibrosis and tubular atrophy percentage and higher injury score. In multivariate analysis, only the maximal 24-h proteinuria and interstitial fibrosis and tubular atrophy percentage were independent predictors of this outcome. The results suggest that morphometric analysis, mainly quantitative measurement of interstitial fibrosis and tubular atrophy percentage, injury score, glomerular basement membrane thickness and glomerulopathy index could be used as an additional method for risk stratification of patients with idiopathic membranous nephropathy.     

Antibodies to glycolipids activate complement and promote proteinuria in passive Heymann nephritis.

Passive Heymann nephritis is an experimental rat model of human membranous nephropathy induced by injection of antisera against crude renal cortical fractions such as Fx1A or rat tubular microvilli. This results in the formation of subepithelial immune deposits, the activation of the C5b-9 membrane attack complex of complement, and severe proteinuria. While the formation of immune deposits is attributed to in situ immune complex formation with antibodies specific for the gp330-Heymann nephritis antigenic complex (HNAC), activation of complement and proteinuria appear to be caused by at least one additional antibody species present in anti-Fx1A sera. We have separated by affinity absorption polyspecific antisera against Fx1A and rat microvilli into one IgG fraction directed specifically against microvillar proteins (anti-Fx1A-prot) and another IgG fraction specific for glycolipids (ant-Fx1A-lip) of tubular microvilli. When injected into rats, the anti-Fx1A-prot fraction induced immune deposits but failed to activate complement or produce proteinuria, similar to results obtained with affinity-purified anti-gp330 IgG. When the antibodies of the anti-Fx1A-lip fraction were injected alone they did not bind to glomeruli. By contrast, when the IgGs specific for the Fx1A-prot fraction (or for gp330-HNAC) were combined with those directed against the Fx1A-lip glycolipid preparation, immune deposits were formed, in situ complement activation was observed, and also proteinuria was induced. It is concluded that within anti-Fx1A and anti-microvillar sera there are at least two IgG fractions of relevance for the development of PHN: one directed against the gp330-HNAC complex which is responsible for the development of immune deposits, and a second specific for glycolipid antigen(s) which activate(s) the complement cascade.     

Peritubular capillary control of proximal tubule reabsorption in the rat.

Changes in peritubular capillary hydrostatic and oncotic pressures, which probably affect net interstitial pressure and, thus, the force on fluid movement across the tubule basement membrane, can modulate absolute proximal reabsorption rate (APR). To examine the relationship between APR and net interstitial pressure, we measured peritubular capillary hydrostatic and oncotic pressure, single nephron filtration rate, APR, absolute distal reabsorption (ADR), and tubular hydrostatic pressure in hydropenic, saline-loaded, and plasma-loaded rats. Net interstitial pressure in saline loading was estimated from subcapsular hydrostatic pressure and lymph protein concentration measurements. The surface area-hydraulic conductivity product of the peritubular capillary network was estimated from these measurements with a model of capillary fluid exchange in which fluid uptake was defined to be APR plus ADR. The estimated value was assumed to remain constant in all three states, and was then used to estimate net interstitial pressure in hydropenic and plasma-loaded rats. APR and net interstitial pressure correlated strongly, a finding consistent with the hypothesized role for net interstitial pressure in regulating proximal reabsorption.     

An analysis of the determinants of nephron filtration rate.

Studies on glomerular filtration in the Munich-Wistar rat, a strain with surface glomeruli, have permitted for the first time the evaluation of the four factors that determine filtration rate: 1) the rate of nephron plasma flow (RPF), 2) the glomerular hydrostatic pressure gradient (deltaP) from capillary to Bowman's space, 3) systemic oncotic pressure (piA), and 4) the glomerular permeability coefficient (LpA), and their respective roles in producing change in filtration rate. The process of filtration in the Munich-Wistar rat is characterized by filtration pressure equilibrium and, therefore, filtration should be highly plasma flow-dependent. Analysis of data from this strain suggests that multiple factors can change LpA, and, at least in animals which do not achieve filtration pressure equilibrium, these alterations in LpA can influence the final filtration rate. Multivariate statistical analysis in a variety of experimental conditions in the Munich-Wistar rat suggest that changes in RPF remain the major mediator of change in nephron filtration rate, both in rats at filtration pressure equilibrium and in disequilibrated animals. Although the glomerulus is an ultrafilter driven by hydrostatic forces, changes in deltaP assume a lesser role in producing alterations in filtration rate.     

Effects of some vasodilator drugs on transcapillary fluid exchange in renal cortex.

In 23 Munich-Wistar rats with surface glomeruli, the determinants of glomerular ultrafiltration and peritubular capillary uptake of proximal reabsorbate were studied before and during intra-arterial infusions of mildly vasodepressor doses of prostaglandin E1,acetylcholine, and bradykinin. For each drug single-nephron glomerular filtration rate remained unchanged from normal hydropenic values while glomerular plasma flow rate increased, resulting in declines in single-nephron filtration fraction (SNFF). Mean glomerular transcapillary hydraulic pressure difference (delta P) increased or remained unchanged on average. Declines in SNFF were accompanied by reductions in efferent arteriolar oncotic pressure (piE). Filtration pressure equilibrium, equality between pi E and delta P, obtained before but not during drug infusions. In the latter situation values for the glomerular capillary ultrafiltration coefficient were calculated and found to be significantly reduced from published control values. Despite marked falls in pi E during drug infusion, absolute proximal reabsorption was not reduced significantly, due, it is suggested, to the opposing effects of increases in efferent arteriolar plasma flow and interstitial hydraulic pressure.     

被动型Heymann肾炎模型的建立及其发病机制的探讨

从正常大鼠肾小管刷状缘微绒毛上提取致病的小管抗原(Tub-Ag)免疫白兔可获得相应的抗血清。给大鼠被动注射此种抗血清后5分钟荧光检测即可见鼠肾小球毛细血管壁上出现兔抗体IgG。约1周后,实验鼠便产生了典型的膜性肾炎样的临床及病理学改变。应用小管抗体(Tub-Ab)进行鼠肾动脉灌注实验,结果表明:在缺乏CIC的情况下,灌注的抗体能与GBM上皮侧、裂隙孔等处结合,IC出现的部位与PHN大鼠IC的位置基本相似。上述实验均提示:PHN的发病机制乃是Tub-Ab与肾小球中固定的抗原直接结合,进而导致上皮下IC原位形成。     

雷帕霉素减缓大鼠被动Heymann肾炎的进展

 目的：观察雷帕霉素对大鼠被动Heymann肾炎（PHN）的影响,并探讨自噬在其中的作用。方法：雄性SD大鼠随机分为3组,即对照组、PHN模型组和雷帕霉素治疗组。以造模后第21天为观察结点,采用全自动生化分析仪测定24 h尿蛋白总量、血尿素氮和血清肌酐,过碘酸-六次甲基四胺银染色观察肾脏病变,Weibel-Gomez点计数方法计数足细胞数量,免疫荧光染色检测肾小球内C5b-9的沉积,免疫组化染色观察caspase-3的表达,Western blotting检测肾小球LC3的表达。结果：雷帕霉素明显减轻PHN模型大鼠的蛋白尿排出（P<0.05）,同时各组大鼠的肾功能均正常,其间无显著差异;雷帕霉素使PHN大鼠肾小球基底膜增厚的程度和范围有所减轻;雷帕霉素明显改善PHN大鼠足细胞缺失情况,减少足细胞凋亡;雷帕霉素可增强肾小球内固有细胞的自噬水平。结论：在PHN的病变过程中,适度增强自噬减少足细胞凋亡,减轻肾脏病变和缓解蛋白尿,可能是雷帕霉素减缓大鼠PHN进展的重要机制之一。     

Complement and leukocyte independent proteinuria and eicosanoid synthesis in rat membranous nephropathy

We examined the effect of complement depletion and leukocyte depletion on an experimental model of membranous nephropathy. Nephrosis was induced in 200-gm male Sprague-Dawley rats by priming with cationic bovine gamma-globulin in adjuvant on day 1 followed by intravenous challenge with antigen starting on day 10. No naive control rats had immunofluorescent deposits in glomeruli; urine protein was less than 10 mg/24 hour and glomerular thromboxane synthesis was 658 +/- 64 ng/mg glomerular dry weight. In contrast, all rats primed and challenged with cationic bovine gamma-globulin had intense granular capillary wall deposits of rats IgG, bovine gamma-globulin, C3 and C5; severe proteinuria (183 +/- 24 mg/24 hour) was observed, associated with a 3-fold increase in glomerular thromboxane (2,393 +/- 574 ng/mg, all p less than 0.01 versus naive controls). In some rats, administration of cobra venom factor and antiserum to rat C3, starting on day 8 was used to deplete complement; hemolytic C3 and C5 were less than 2% of normal at sacrifice. These rats had IgG and bovine gamma-globulin deposits, whereas they lacked glomerular C3 or C5. Proteinuria (209 +/- 28 mg/24 hour) and glomerular thromboxane (2,087 +/- 394 ng/mg) were markedly increased compared with control, but no different from normocomplementemic rats primed and challenged with cationic bovine gamma-globulin. In other rats, depletion of leukocytes was achieved by 1,000 R x-irradiation on day 7; at sacrifice, irradiated rats had 1,270 +/- 462 wbc/microliter versus 10,375 +/- 1,652 in nephrotic rats given no other treatment, with unaltered differentials. These rats had glomerular deposits of rat IgG, bovine gamma-globulin, C3 and C5 indistinguishable from nephrotic rats with normal leukocyte counts in intensity and distribution. Proteinuria (202 +/- 30) and glomerular thromboxane (2,358 +/- 189 ng/mg) were markedly elevated compared with naive controls, but were not different from the normocomplementemic or complement-depleted groups primed and challenged with antigen. An additional control group included rats primed with ovalbumin on day 1, irradiated with 1,000 R on day 7, and challenged with cationic bovine gamma-globulin starting on day 10. This group had granular capillary wall deposits of bovine gamma-globulin, but not deposits of IgG, C3, or C5; urine protein excretion (less than 10 mg/24 hours) and glomerular thromboxane synthesis (613 +/- 90) were not different from naive controls. Glomerular prostaglandin E2 synthesis did not differ among the five groups.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of complement in acute tubulointerstitial injury of rats with aminonucleoside nephrosis.

The present work was designed to elucidate the in vivo role of complement in the proteinuria-associated tubulointerstitial injury. Rats were intravenously injected with puromycin aminonucleoside, and massive proteinuria was observed within 5 days. Prominent tubulointerstitial injury characterized by proximal tubular degeneration, tubular dilatation, and leukocyte infiltration were observed 7 days after injection. C3 and C5b-9 were observed in the luminal side of proximal tubular cells. Renal function, assessed by inulin and para-aminohippurate clearance, was significantly decreased. To-assess the role of complement in this model, rats were injected with either cobra venom factor or soluble recombinant human complement receptor type 1 starting at day 3. These manipulations significantly improved tubulointerstitial pathology and para-aminohippurate clearance without affecting the degree of proteinuria. Deposition of C3 and C5b-9 was not detected in the kidney of rats depleted of complement by cobra venom factor. In rats treated with soluble complement receptor, C3 was still detected in the tubules, but deposition of C5b-9 was not observed. Soluble complement receptor was detected at the site of C3 deposition and in the urine. These data strongly suggest that complement plays a pivotal role in proteinuria-associated tubulointerstitial injury and that systemic complement depletion or inhibition of complement in the tubular lumen may diminish the tubulointerstitial damage.     

Complement and monocytes are essential for provoking glomerular injury in passive Heymann nephritis in rats. Terminal complement components are not the sole mediators of proteinuria

Complement but not polymorphonuclear granulocytes (PMN) causes glomerular injury in passive Heymann nephritis in rats. We have now identified monocytes as another important mediator in this model. Passive Heymann nephritis was induced in Wistar rats by intravenous injection of sheep anti-rat Fx1A antiserum. Four groups (all receiving anti-rat Fx1A antiserum) were studied: (a) rats given normal sheep globulin (nephritic controls), (b) rats given sheep anti-rat PMN globulin (PMN-depleted), (c) rats given sheep anti-rat monocyte globulin (monocyte-depleted), (d) rats injected with cobra venom factor (complement-depleted). In vitro specificity controls for anti-cell antisera were made by cytotoxicity tests and inhibition of phagocytosis. In vivo specificity controls were performed in heterologous Masugi nephritis (PMN-dependent) and accelerated Masugi nephritis (monocyte-dependent). Complement and monocyte depletion significantly delayed the onset of proteinuria (p less than 0.001 versus nephritic controls on day 5), PMN depletion had no significant effect. Monocyte infiltration was seen in control nephritic rats, but monocyte depletion prevented this influx. In the monocyte-depleted group, no differences in glomerular deposition of C3, C9, and C5b-9 were seen in comparison to the nephritic control rats. Serum C3 levels were comparable in groups a, b, and c, the complement system was biologically active in the monocyte depleted-group (c), and the amount of anti-Fx1A antibody bound was the same in all groups. This shows that, besides complement, monocytes are required for induction of renal damage in passive Heymann nephritis. The concept of a sole role for complement in glomerular immune injury involving subepithelial immune deposits should be reconsidered.     

Effect of vanadate on renal tubular function in rats

Orthovanadate (VO4) has been shown to cause a marked natriuresis in rats. This has been ascribed to its inhibitory action on renal Na-K-ATPase activity. Because virtually all nephron segments possess Na-K-ATPase activity the administration of VO4 should alter renal tubular transport along the entire nephron. To examine this possibility, adult rats were anesthetized and infused with VO4 (10 mumol.kg body wt-1.h-1 i.v.). This dose had no effect on glomerular filtration rate, effective renal plasma flow, and blood pressure, whereas urine flow and sodium and water excretion rose markedly. Potassium excretion remained unaltered. VO4 depressed only maximal bicarbonate and glucose reabsorption without causing a glucose or bicarbonate "leak" at normal levels of blood glucose or bicarbonate. In acutely thyroparathyroidectomized rats VO4 produced a striking phosphaturia, not accompanied by an increase in nephrogenous cAMP excretion. Both free water clearance in Brattleboro rats and free water reabsorption in normal rats was significantly depressed by VO4. These data demonstrate that VO4 depresses tubular reabsorption in proximal and distal nephron segments. We conclude that VO4 exerts its effect on tubular function by inhibition of Na-K-ATPase activity.     

Depletion of C6 prevents development of proteinuria in experimental membranous nephropathy in rats.

To study the possible role of the complement membrane attack complex, C5b-9, in an experimental rat model that is morphologically indistinguishable from membranous nephropathy in man (passive Heymann nephritis [PHN]), an antibody to rat C6 was used to deplete C6 levels to less than 5% of pretreatment values (C6D) during disease development. C3, C7, C8, and C9 levels were not different in C6D and control rats. After injection of nephritogenic quantities of 125I-anti-Fx1A antibody, the kinetics of disappearance of labeled IgG from the blood were identical in the complement deficient and sufficient groups, and glomerular deposition of 125I-antibody was the same in both groups at 5 days. Glomerular deposits of sheep IgG and C3 were also similar in C6D and controls, but glomerular deposits of C6 and C5b-9 neoantigens were markedly reduced or absent in C6 depleted rats. However, despite equivalent antibody deposits, proteinuria was abolished in C6D rats compared with normocomplementemic controls. Similar results were obtained when F(ab')2 anti-rat C6 IgG was used to deplete C6 during development of PHN. These results demonstrate that C6 is required for the development of the increased glomerular permeability that occurs in PHN, presumably because C6 is required for formation of C5b-9. We conclude that glomerular injury in the PHN model of membranous nephropathy in the rat is mediated by C5b-9.     

Renal corpuscular hydrodynamics: Digital computer simulation

Summary A mathematical model of the renal corpuscle is presented and used to quantify the effect on filtration rate, nephron blood flow and hydrostatic pressure in the glomerular capillaries of variations in: 1. the hydrostatic pressure in Bowman's space; 2. the hydrodynamic resistances of the afferent and efferent arterioles; 3. the ultrafiltration coefficient of the glomerular membrane; 4. the hydrostatic pressure in the peritubular capillaries; 5. the arterial haematocrit and plasma protein concentration. The model is derived from the principle of conservation of mass and volume. Hydrostatic pressure gradients along the glomerular capillaries are neglectec. The hydrodynamic resistances of the afferent and efferent arterioles are assumed to be determined by two independent factors, one being determined by the vascular dimensions, the other by the haematocrit. Blood flow is considered to be related in a linear manner to the hydrostatic pressure decreases along these vessels. The effect of changing the hydrostatic pressure in Bowman's space on nephronGFR was calculated and found to agree with experimental measurements. When corpuscular hydrodynamics are related to variations in the hydrodynamic resistance of the afferent or efferent arteriole it is seen that the change in efferent arteriolar plasma flow accompanying altered nephronGFR is very sensitive to the way in which the change is produced. In contrast changes in glomerular capillary pressure and filtration fraction are insensitive. The calculations indicate that differences measured in nephronGFR between superficial and juxtamedullary nephrons can be explained by assuming that the diameters of the afferent and efferent arterioles of the juxtamedullary nephrons increase in direct proportion to the diameter of the renal corpuscle.