Severe systemic vascular necrosis in cyclosporin-treated rabbits with acute serum sickness.

Rabbits given acute serum sickness (ASS) and treated with cyclosporin A (CyA) developed a severe, systemic vascular injury, which was not similar to that normally seen in ASS. Thirty-three NZW rabbits received a single intravenous injection of 250 mg/kg bovine serum albumen (BSA) with or without endotoxin (5 micrograms/kg), on day 0. Groups of rabbits were given intramuscular CyA as follows: 15 mg/kg/day from day -2 to +8, or 25 mg/kg/day from day -2 to +3 or day 0 to 5. Muscular arteries of the heart and splanchnic organs developed an arterial injury in which there was extensive fibrinoid necrosis of the vessel wall but little or none of the mononuclear cell reaction that is normally associated with the arteritis of ASS. A microvascular injury also occurred which led to interstitial haemorrhage in the gastric mucosa and multi-focal necrosis in the heart and liver. These lesions were seen with equal frequency in all groups of rabbits with serum sickness who received CyA, irrespective of whether they also received endotoxin. We suggest that CyA altered the host inflammatory response to the injury initiated by the BSA-anti-BSA immune complexes and this led to enhanced vascular injury. The inhibition by CyA of the perivascular cellular reaction suggests that this reaction may be mediated by T lymphocytes. This model should provide further insight into the pathogenesis of arteritis, as well as the mechanisms of cyclosporin toxicity.     

Severe systemic vascular necrosis in cyclosporin-treated rabbits with acute serum sickness

Rabbits given acute serum sickness (ASS) and treated with cyclosporin A (CyA) developed a severe, systemic vascular injury, which was not similar to that normally seen in ASS. Thirty-three NZW rabbits received a single intravenous injection of 250 mg/kg bovine serum albumen (BSA) with or without endotoxin (5 micrograms/kg), on day 0. Groups of rabbits were given intramuscular CyA as follows: 15 mg/kg/day from day -2 to +8, or 25 mg/kg/day from day -2 to +3 or day 0 to 5. Muscular arteries of the heart and splanchnic organs developed an arterial injury in which there was extensive fibrinoid necrosis of the vessel wall but little or none of the mononuclear cell reaction that is normally associated with the arteritis of ASS. A microvascular injury also occurred which led to interstitial haemorrhage in the gastric mucosa and multi-focal necrosis in the heart and liver. These lesions were seen with equal frequency in all groups of rabbits with serum sickness who received CyA, irrespective of whether they also received endotoxin. We suggest that CyA altered the host inflammatory response to the injury initiated by the BSA-anti-BSA immune complexes and this led to enhanced vascular injury. The inhibition by CyA of the perivascular cellular reaction suggests that this reaction may be mediated by T lymphocytes. This model should provide further insight into the pathogenesis of arteritis, as well as the mechanisms of cyclosporin toxicity.     

Cyclosporin A and anti-glomerular basement membrane antibody glomerulonephritis in rats

In a telescoped model of antiglomerular basement membrane (GBM) antibody induced nephritis, Lewis strain rats were injected in the footpad with rabbit IgG on day 0 and then given a single intravenous injection of rabbit anti-rat GBM antibody on day 5. Proteinuria developed within 24 h and renal histology 7 days later showed a focal or diffuse proliferative glomerulonephritis. In this study rats treated as above were given Cyclosporin A (CyA) 20 mg/kg daily by intraperitoneal injection from day 0 or from day 5. Rats given CyA plus anti-GBM antibody developed extensive glomerular infiltration with polymorphs and glomerular thrombosis, lesions not seen with unmodified anti-GBM nephritis or in rats who received CyA alone. The mechanism by which CyA given prior to or at the onset of immunological insult in this model worsens glomerular injury is unclear.     

Cyclosporin A and anti-glomerular basement membrane antibody glomerulonephritis in rats.

In a telescoped model of antiglomerular basement membrane (GBM) antibody induced nephritis, Lewis strain rats were injected in the footpad with rabbit IgG on day 0 and then given a single intravenous injection of rabbit anti-rat GBM antibody on day 5. Proteinuria developed within 24 h and renal histology 7 days later showed a focal or diffuse proliferative glomerulonephritis. In this study rats treated as above were given Cyclosporin A (CyA) 20 mg/kg daily by intraperitoneal injection from day 0 or from day 5. Rats given CyA plus anti-GBM antibody developed extensive glomerular infiltration with polymorphs and glomerular thrombosis, lesions not seen with unmodified anti-GBM nephritis or in rats who received CyA alone. The mechanism by which CyA given prior to or at the onset of immunological insult in this model worsens glomerular injury is unclear.     

Interaction of Angiotensin with Disseminated Intravascular Coagulation: A Possible Mechanism in the Genesis of Acute Renal Failure

Because of the importance of the renin-angiotensin system in renal homeostatic mechanisms, the effect of angiotensin administration upon disseminated intravascular coagulation has been studied in rabbits. An infusion of angiotensin II (0.1 μg/kg/min for 2 hours) produced neither histologic abnormalities in the kidneys nor an elevation of creatinine. After an infusion of thrombin (2.0 units/kg/min for 2 hours) only 3 of 10 rabbits, when sacrified 24 hours later, showed histologic lesions comprised of occasional fibrin thrombi and foci of tubular necrosis. Creatinine levels did not rise. In contrast, the combination of angiotensin and thrombin resulted in renal lesions in 12 of 14 animals. Four had frank cortical necrosis, while combinations of tubular necrosis, glomerular thrombosis and segmental glomerular infarction occurred in the others, together with elevated creatinine levels. Blockade of α-adrenoreceptors with phenoxybenzamine in 12 animals did not prevent either these histologic changes or creatinine elevation, showing that the effect of angiotensin was independent of α-adrenoreceptor stimulation. The synergistic interaction between angiotensin and disseminated intravascular coagulation was not explained by differences in the consumption of plasma fibrinogen but apparently was due to localization of fibrin thrombi within glomerular capillaries by the vasomotor actions of angiotensin, as has previously been shown to occur with α-adrenoreceptor simulation. Such a mechanism might contribute to renal glomerular deposition of fibrin in acute ischemic renal failure.     

Vasoactive agents and production of thrombosis during intravascular coagulation. 2. alpha-Adrenergic stimulation: effects and mechanisms

The mechanism whereby norepinephrine elicits thrombosis during intravascular coagulation was investigated further in rabbits given a 4 h infusion of thrombin (1 NIH unit/kg/min). Norepinephrine (3 micrograms/kg/min) combined with thrombin produced glomerular capillary thrombosis in all animals as compared to 4.3% with thrombin alone. Alpha-adrenergic receptors mediated this effect, as indicated (a) by prevention of glomerular thrombosis by dibenzyline but not by methysergide, and (b) by failure of histamine or acetylcholine combined with thrombin to induce the phenomenon. However, in combination with thrombin, these two agents induced duodenal mucosal microthrombosis. Study of the glomerular circulation with colloidal carbon showed that norepinephrine elicits severe glomerular capillary stasis in thrombin treated rabbits; the vasomotor reaction precedes increased fibrinogen consumption and focal deposition of fibrin in the glomeruli. Pretreatment with dibenzyline prevented glomerular stasis and reduced fibrinogen consumption. The phagocytic activity of the reticulo-endothelial system was increased 7 times by thrombin infusions, with or without norepinephrine. We conclude that stimulation of the alpha 1-adrenergic receptors triggers glomerular thrombosis by production of severe glomerular stasis which localizes formation of thrombi in the dilated vessels. These results provide a rational explanation for the role of alpha-adrenergic stimulation in the endotoxin-induced generalized Shwartzman reaction and outline some of the mechanisms and agents implied in the selection of the target organs for thrombosis during intravascular coagulation.     

Initiation and recovery processes of endotoxin induced disseminated intravascular coagulation (DIC): scanning and transmission electron microscopic observations of rat renal tissues

To clarify the initiation, development and recovery processes of disseminated intravascular coagulation (DIC), rat glomerular capillaries and fibrin thrombi were examined under transmission and scanning electron microscopes. DIC was induced in rats by a single intraperitoneal injection of endotoxin (Et., 7.5 mg/kg lipopolysaccharide:B, E. coli 026:B6). At 2 h after Et. injection, the endothelial surface of the glomerular capillary became irregular with projections like a sea anemone. At 4 h after Et. injection, agglomerated fibrin thrombi composed of fibrin fiber bundles with fine cross-striated fibriform structures were observed in the capillary lumen. The fibrin thrombi gradually changed into fine reticular systems suggesting a degradation process by 6 h after Et. injection, and formed a coarse granular agglomerate by 8 h after Et. injection. These fibrin thrombi disappeared within 12 h of Et. injection, but the endothelial surface remained edematous. At 24 h after Et. injection, the microstructure of the glomerular capillaries returned normal. Based on these observations, we concluded that DIC was primarily initiated by injury to the capillary endothelium, and that changes on the endothelial surface contributed to the development of DIC.     

Mesangiolysis: an important glomerular lesion in thrombotic microangiopathy

Six cases of malignancy-associated thrombotic microangiopathy and eight cases of idiopathic microangiopathy have been studied by renal biopsy. All patients of both groups had mild to severe renal impairment and microangiopathic hemolytic anemia. The renal lesions were histopathologically identical in the two groups. The most characteristic abnormalities were glomerular mesangiolysis and glomerular and arteriolar thrombosis. Subendothelial widening, presumably due to entrapment of blood components, and the formation of capillary and arteriolar thrombi may be attributed to endothelial damage. Glomerular fibrinogen was demonstrated by immunofluorescence in a majority of cases. Immunofluorescence also showed glomerular immunoglobulin M (IgM) and Clq in a majority of cases and C3 in slightly less than half. Mesangiolysis, present in every case, resulted in coalescence of capillary lumina, but mesangiolysis is a bland process, easily overlooked. The mesangial waists of the glomerular tufts seemed to unravel and come apart, with no inflammatory reaction or fibrin deposition on the luminal surface. The presence of capillary enlargement was confirmed morphometrically as an increased proportion of glomerular sectional area. In what appeared to be a late stage of mesangiolysis, the mesangium was thickened by pale fibrillary material, producing a lobulated glomerular tuft and eventual glomerular solidification. The early stages of mesangiolysis may be reflected only in glomerular capillary ectasia, whereas the late stages produce a distinctive form of glomerular sclerosis.     

Glomerular thrombi in renal allografts associated with cyclosporin treatment.

We have found glomerular capillary thrombi or afferent arteriolar thrombosis in eight renal biopsy specimens from seven renal allograft recipients. All patients were receiving cyclosporin and prednisolone. Biopsies were performed either routinely one and four weeks after transplantation or during periods of renal dysfunction. None of the patients whose biopsy material contained glomerular thrombi was considered, in retrospect, to have been undergoing rejection at the time of biopsy. Thrombi consisted of finely granular material partially obstructing glomerular capillaries. By light microscopy the staining characteristics of the thrombi were compatible with platelet-fibrin aggregates, and this was confirmed by immunoperoxidase examination. Such thrombi have not previously been seen in biopsy material from patients treated with prednisolone and azathioprine, except rarely associated with acute vascular injection. In none of these patients was there haematological evidence of the haemolytic uraemic syndrome as has been reported in bone marrow recipients treated with cyclosporin.     

Tumor necrosis factor induces glomerular damage in the rabbit.

Tumor necrosis factor (TNF) is a polypeptide hormone produced by activated macrophages detectable in the circulation of experimental animals given endotoxin. Recent evidence strongly suggests that many of the deleterious effects of endotoxin in experimental animals are mediated by TNF. Because endotoxemia in experimental animals and humans is associated with glomerular damage the present investigation was designed to establish whether TNF directly induces glomerular functional and structural changes. Twenty-three rabbits were given human recombinant TNF at the doses of 0.08, 0.8, and 8.0 micrograms/kg/h as a continuous 5-hour intravenous infusion. Animals were killed at the end of the infusion. All rabbits given 0.8 and 8.0 micrograms/kg/h TNF developed anemia (Ht value decrease at 5 hours: 0.8 microgram/kg/h, 15%; 8.0 micrograms/kg/h, 16%); leukopenia (leukocyte count decrease at 5 hours: 0.8 micrograms/kg/h, 47%; 8.0 micrograms/kg/h, 59%); thrombocytopenia (platelet count decrease at 5 hours; 0.8 micrograms/kg/h, 45%; 8.0 micrograms/kg/h, 57%). Rabbits given 8.0 micrograms/kg/h also had renal failure (serum creatinine from 1.02 +/- 0.15 to 1.64 +/- 0.34 mg/dl). By light microscopy only occasional polymorphonuclear leukocytes in the glomerular capillaries were detectable in rabbits infused with 0.08 micrograms/kg/h TNF, whereas with 0.8 micrograms/kg/h TNF the presence of inflammatory cells in the glomerular capillaries was the prominent finding. With 8.0 micrograms/kg/h TNF beside leukocyte accumulation, fibrin was detected in the glomerular capillary lumens of two of eight animals. Electron microscopy found dose-dependent glomerular endothelial cell damage in animals given TNF with fibrinlike material in the capillary lumens. Glomerular changes induced by TNF were remarkably similar to those previously found in animals given endotoxin. Thus, TNF is likely to be the mediator of endotoxin-induced glomerular damage and can be regarded as a new mediator of macrophage-dependent damage in glomerulonephritis.     

Vascular endothelial growth factor enhances glomerular capillary repair and accelerates resolution of experimentally induced glomerulonephritis

Vascular endothelial growth factor (VEGF) regulates angiogenesis through endothelial cell proliferation and plays an important role in capillary repair in damaged glomeruli. We tested the hypothesis that VEGF might be beneficial in rats with severe glomerular injury in glomerulonephritis (GN) based on its angiogenic and vascular remodeling properties. Acute GN with severe glomerular destruction was induced in rats by injection of anti-Thy-1.1 antibody (day 0) and Habu-snake venom (day 1). Rats were intraperitoneally injected with recombinant human VEGF(165) (10 microg/100 g body wt/day) or vehicle from day 2 to day 9, and monitored changes in glomerular capillaries, development of glomerular inflammation, and progression to glomerular sclerosis after acute glomerular destruction in both groups. Rats that received anti-Thy-1.1 antibody and Habu-snake venom showed severe mesangiolysis and marked destruction of capillary network on day 2. VEGF was expressed on glomerular epithelial cells, proliferating mesangial cells, and some infiltrating leukocytes, and VEGF(165) protein levels increased in damaged glomeruli during day 5 to day 7. Normal, damaged, and regenerating glomerular endothelial cells expressed VEGF receptor flk-1. However, endothelial cell proliferation and capillary repair was rare in vehicle-treated rats with severe glomerular damage, which progressed to global sclerosis and chronic renal failure by week 8. In contrast, in the VEGF-treated group, VEGF(165) significantly enhanced endothelial cell proliferation and capillary repair in glomeruli by day 9 (proliferating endothelial cells: VEGF(165), 4.3 +/- 1.1; control, 2.2 +/- 0.9 cells on day 7, P < 0.001; and glomerular capillaries: VEGF(165), 24.6 +/- 4.8; control, 16.9 +/- 3.4 capillaries on day 7, P < 0.01). Thereafter, damaged glomeruli gradually recovered after development of capillary network by week 8, and significant improvement of renal function was evident in the VEGF-treated group during week 8 (creatinine: VEGF(165), 0.3 +/- 0.1; control, 2.6 +/- 0.9 mg/dl, P < 0.001; proteinuria: VEGF(165), 54 +/- 15; control, 318 +/- 60 mg/day, P < 0.001). We conclude that the beneficial effect of VEGF(165) in severe glomerular injury in GN emphasizes the importance of capillary repair in the resolution of GN, and may allow the design of new therapeutic strategies against severe GN.     

Rare glomerular capillary regeneration and subsequent capillary regression with endothelial cell apoptosis in progressive glomerulonephritis.

Glomerulonephritis (GN) leading to glomerular sclerosis remains an important cause of renal failure. The glomerulus is a capillary network, but endothelial and vascular reactions during progressive GN are not well understood. We have, therefore, examined the morphological alterations of glomerular capillary network and endothelial cells during the progression of damaged glomeruli to glomerular sclerosis. A progressive model of anti-glomerular basement membrane (GBM) GN was induced in Wistar-Kyoto (WKY) rats with a single injection of anti-rat GBM antibody. Severe necrotizing glomerular injuries were observed between day 5 and week 3 with a reduction in the number of total glomerular endothelial cells and total glomerular capillary lumina per glomerular cross sections. In necrotizing lesions, the glomerular endothelial cells were lost with the destruction of the glomerular capillary network. Moreover, angiogenic capillary repair with proliferation of endothelial cells was rare in severely damaged regions of glomeruli. Subsequently, mesangial hypercellularity and marked mesangial matrix accumulation occurred with absence of the development of a capillary network, and the necrotizing lesions progressed to sclerotic scars until 8 weeks. Although active necrotizing lesions could not be seen in damaged glomeruli between week 4 and week 8, the number of apoptotic endothelial cells gradually increased in the glomerular capillaries (0.10 +/- 0.01 apoptotic endothelial cells/glomerular cross section at week 8 versus 0.00 +/- 0.00 control cells (mean +/- SEM; P < 0.05) with the progression of glomerular sclerosis. Whereas the number of apoptotic endothelial cells increased in the damaged glomeruli, the number of total glomerular endothelial cells decreased (9.3 +/- 3.0 cells/glomerular cross section at week 8 versus 24.8 +/- 3.0 cells in control (mean +/- SD); P < 0.001) with regression of glomerular capillaries (3.6 +/- 2.5 capillary lumina/glomerular cross section at week 8 versus 35.0 +/- 5.0 capillary lumina in control (mean +/- SD); P < 0.001). Finally, glomerular endothelial cells could not be detected in the sclerotic lesions in progressive anti-GBM GN in WKY rats. These data indicate that the destruction of the capillary network of glomeruli and subsequent incomplete angiogenic capillary repair leads to glomerular sclerosis in progressive GN. Endothelial cell apoptosis with glomerular capillary regression may also contribute to the development of glomerular sclerosis. Injury of the glomerular capillary network with endothelial cell damage, including apoptosis and subsequent incomplete capillary repair, plays an important role in the progression of glomerular sclerosis during anti-GBM GN in WKY rats.     

Glomerular fibrin thrombi in ABO and crossmatch compatible renal allograft biopsies

Glomerular fibrin thrombi may be an early indication of antibody-mediated rejection in renal allograft biopsies. However, fibrin thrombi have a broad differential; thus, we sought to evaluate the etiology and implications of glomerular fibrin thrombi in allograft biopsies of blood group and cytotoxic crossmatch compatible renal allografts.Biopsies were identified from the pathology files of Oregon Health & Science University. Detailed histopathologic findings were retrospectively correlated with clinical data, treatment, and outcome.Sixteen early posttransplant biopsies had glomerular fibrin thrombi, including three surveillance biopsies. Six of 16 biopsies had no other histopathologic findings; 5/16 had glomerulitis and peritubular capillaritis; 4/16 had concomitant cellular vascular rejection; one had parenchymal infarction. C4d staining was positive in 4/16 cases. Most patients were treated with IVIg and plasmapheresis, others with rapamycin, thymoglobulin, or rituximab. At an average follow-up of 62 months, 8 patients with functioning grafts had a mean serum creatinine of 1.4 mg/dL (122 μmol/L).Antibody-mediated rejection is an important consideration in blood group compatible allograft biopsies with glomerular fibrin thrombi, even with C4d-negative biopsies. However, multidisciplinary evaluation is necessary, given other etiologies, including drug toxicity, hemolytic-uremia syndrome, and large vessel thrombosis. Despite aggressive treatment, both short and long-term graft survival may be compromised.     

Effects of ancrod and rtPA on fibrin accumulation, glomerular inflammation and renal function in nephrotoxic nephritis.

We have compared the effects of ancrod and recombinant tissue plasminogen activator (rtPA) on nephrotoxic nephritis induced in pre-immunized rabbits by the administration of nephrotoxic globulin (NTG; sheep anti-rabbit glomerular basement membrane). We used three different doses of NTG: in each experiment three groups of six rabbits were preimmunized with normal sheep globulin and given NTG: group A received no further treatment; group B received rtPA, 2 mg/kg 12 hourly; group C received ancrod 2 U/kg 12 hourly. Animals were bled daily for estimation of plasma fibrinogen and serum creatinine, then killed on day 5 and kidneys removed for histology. 1 ml/kg of NTG caused massive glomerular necrosis, all three groups having severe renal failure. With 0.5 ml/kg of NTG, ancrod and rtPA both effectively prevented fibrin deposition in Bowman's space, but all animals had severe proliferative glomerulonephritis and marked renal failure. With 0.25 ml/kg of NTG, control animals developed severe proliferative nephritis and advanced renal failure, ancrod provided almost complete protection, and the rtPA group had renal injury and functional impairment intermediate between the other two groups. We conclude that renal failure in severe nephrotoxic nephritis is fibrin-independent, but in less fulminant nephritis renal function can be protected by defibrination with ancrod. rtPA is capable of reducing glomerular fibrin accumulation as effectively as ancrod, but provides inferior protection of renal function.     

Cyclosporin A inhibits acute serum sickness nephritis in rabbits.

The effect of the immunosuppressive agent cyclosporin A (Cy A) on the renal injury in acute serum sickness was examined in rabbits. Serum sickness was induced in 23 untreated NZW rabbits by a single intravenous injection of bovine serum albumin (BSA) 250 mg/kg with E. coli endotoxin (5 micrograms/kg): BSA was eliminated after 8.6 +/- 0.16 days (mean +/- s.e. (mean]; proteinuria occurred in 19 (84%) and glomerular proliferation in 20 (87%) rabbits. When Cy A (15 or 25 mg/kg) was given daily by intramuscular injection, starting either 2 days before or at the time of induction of acute serum sickness, proteinuria was profoundly reduced and glomerular proliferation was inhibited. Even when rabbits were first treated with Cy A (25 mg/kg) 5 days after the induction of disease proteinuria and glomerular proliferation were similarly inhibited. When the treated animals were compared with controls there were no differences in the following: time to elimination of BSA, amount or size of circulating immune complexes, fall in serum C3 at immune elimination, or deposition of immune reactants in the glomeruli. These results show that Cy A inhibits the renal injury of acute serum sickness and indicate that T cells may play a role in mediating the nephritis in this condition.     

Mitomycin C associated hemolytic uremic syndrome

Mitomycin C associated Hemolytic Uremic Syndrome (HUS) is a potentially fatal but uncommon condition that is not yet widely recognised. It consists of microangiopathic hemolytic anemia, thrombocytopenia and progressive renal failure associated with mitomycin C treatment and affects about 10% of patients treated with this agent. The renal failure usually develops about 8-10 mth after start of mitomycin C treatment and the mortality is approximately 60% from renal failure or pulmonary edema. Renal lesions are similar to those seen in idiopathic HUS and include arteriolar fibrin thrombi, expanded subendothelial zones in glomerular capillary walls, ischemic wrinkling of glomerular basement membranes and mesangiolysis. The mechanism of action is postulated as mitomycin C-induced endothelial cell damage. We describe the clinical course and pathological findings in a 65 yr-old man with gastric adenocarcinoma who developed renal failure and thrombocytopenia while on treatment with mitomycin C and died in pulmonary edema.     

Endothelin-1 expression in scleroderma renal crisis

The objective of the study was to investigate the role of endothelin-1 in the pathogenesis of scleroderma renal crisis in patients with systemic sclerosis. We used immunohistochemical analysis with anti-endothelin-1 and anti-von Willebrand factor antibodies in comparing kidney biopsies from patients with systemic sclerosis and scleroderma renal crisis (n = 14); from normal kidneys (n = 5); and from patients with typical hemolytic uremic syndrome and thrombotic microangiopathy (n = 5), antiphospholipid syndrome (n = 6), diabetic nephropathy (n = 5), minimal change disease with cyclosporine toxicity (n = 5), or nephroangiosclerosis (n = 5). Kidney biopsies from all systemic sclerosis patients presented specific lesions: glomerular lesions with thickened capillary walls (n = 6, 42.8%), mesangiolysis (n = 3, 21.4%), fibrin thrombi (n = 3, 21.4%), hypertrophy of juxtaglomerular apparatus (n = 5, 35.7%), arteriolar lesions showing mucinous intimal thickening and lumen mucoid occlusions (n = 13, 92.8%), proliferation of intimal cells (ie, "onion-skin" lesions; n = 13, 92.8%), fibrinoid necrosis (n = 3, 21.4%), and fibrin thrombosis (n = 4, 28.6%). Chronic lesions in large arteries showed modifications such as fibrous intimal thickening (n = 13, 92.8%). The pattern of endothelial staining for endothelin-1 in both glomeruli and arteriolar lesions appears to be specific for scleroderma renal crisis. Glomerular endothelin-1 staining without arteriolar staining was seen in hemolytic uremic syndrome; and isolated arteriolar staining (without glomerular staining) was seen in a number of conditions including antiphospholipid nephropathy, cyclosporine toxicity, and diabetic nephropathy. Endothelin-1 is overexpressed in glomeruli and arterioles of patients with scleroderma renal crisis, which suggests that endothelin-1 might be a therapeutic target in this condition.     

Renal Involvement in the Antiphospholipid Syndrome (APS)—APS Nephropathy

Although the kidney represents a major target organ in antiphospholipid syndrome (APS), renal involvement in APS was poorly recognized until recently. The most well-recognized renal manifestations of APS are the renal artery thrombosis/stenosis, renal infarction, hypertension, renal vein thrombosis, end-stage renal disease, increased allograft vascular thrombosis, some types of glomerular disease, and a small-vessel vaso-occlusive nephropathy, recently defined as APS nephropathy. APS nephropathy was first described in primary APS patients, characterized by acute thrombotic lesions in glomeruli and/or arterioles (thrombotic microangiopathy) and chronic vascular lesions such as fibrous intimal hyperplasia of arterioles and interlobular arteries, organized thrombi with or without recanalization, and fibrous arterial and arteriolar occlusions or focal cortical atrophy. APS nephropathy was also detected in further studies including patients with systemic lupus erythematosus (SLE)-related APS and SLE/non-APS patients with positive antiphospholipid antibodies, independently of lupus nephritis. The same histologic lesions, especially thrombotic mictroangiopathy, were also observed in patients with catastrophic APS. The most frequent clinical and laboratory characteristics of APS nephropathy in all the above groups of patients are hypertension (often severe), proteinuria (ranging from mild to nephrotic range), hematuria, and acute or chronic renal insufficiency.     

Ureteral blockade sensitizes to the generalized Shwartzman reaction.

Renal cortical necrosis (RCN) has been reported in the normal kidney of patients with a contralateral ureteral occlusion (UO). So far, studies have examined the mechanisms protecting the affected kidney from glomerular thrombosis and cortical necrosis; but to the authors' knowledge, none has ever investigated the potential role of UO on the occurrence of the associated disseminated intravascular coagulation (DIC) episode leading to RCN. Female rats with a ligature of the right or left ureter were given injections, at different times after surgery, of 400 micrograms Salmonella typhosa 0901 endotoxin. Other experimental groups included normal and sham-operation rats and animals with a unilateral nephrectomy or with one kidney rendered ischemic by complete ligature of the renal vessels and of the ureter. All the animals were sacrificed 4 hours after endotoxin, and kidney sections stained with PTAH were examined for the presence of fibrin thrombi. Glomerular thrombosis was never observed in any hydronephrotic kidney, but occurred with a low incidence (16%) in the contralateral organ in the group given endotoxin the second day after UO. The incidence and severity of glomerular capillary thrombosis gradually increased in the normal kidney as the delay between surgery and endotoxin was prolonged; the incidences (P less than 0.01) were 45% and 83%, respectively, after 6 and 10 days. Endotoxin failed totally to initiate the lesion 1 day after UO as well as in normal, sham-operation and unilaterally nephrectomized rats, and in animals with combined UO and ligature of the renal circulation. We conclude that the perfused hydronephrotic kidney liberates a factor(s) that sensitizes to DIC and glomerular thrombosis, typical of the generalized Shwartzman reaction.     

Nonimmunologic mechanisms of glomerular injury

From the above discussion it is clear that many factors have been invoked in the pathogenesis of progressive glomerular injury. Those which are most important include increased PGC, coagulation, serum lipid abnormalities, and hypertrophy. Although many hemodynamic alterations have been identified, increased PGC was noted most constantly. Furthermore, the loss of autoregulatory capability which was observed in some models with progressive glomerulosclerosis usually resulted in increased PGC. Increased PGC has been associated with augmented dietary protein and is seen in the Munich-Wistar rat made diabetic. Such an increase in PGC could cause direct mechanical injury to endothelial and epithelial cells, as well as be responsible for increased mesangial traffic of macromolecules with the potential for stimulating cellular proliferation and mesangial matrix increase. Additional support for the importance of increased PGC is provided by the protective effect of decreasing PGC with CEI therapy and anemia, and by the enhanced autoregulatory capability in both the Milan and Okamoto hypertensive rats. The significance of coagulation factors is confirmed by the formation of platelet and fibrin thrombi in the development of the glomerular lesions. The sequence of glomerular injury suggests that endothelial damage occurs with subsequent formation of platelet aggregates as a response to this injury. Formation of platelet aggregates may be associated with the production of substances potentially injurious to the endothelial cells. Although blocking the appearance of such thrombi by administration of heparin or thromboxane synthetase inhibitor prevents glomerular injury, the blood pressure lowering effect of these agents complicates the interpretation of the studies. Serum lipid abnormalities are also important factors in the progression of nonimmunologic glomerular injury. Such abnormalities are observed with increased dietary phosphorus or lipid, in the obese Zucker rat, and in rats with diabetes mellitus. Reduction in serum cholesterol by administration of clofibric acid or mevinolin diminishes glomerular injury independent of alterations in glomerular hemodynamics. The possible link between increased serum lipids and augmentation of glomerular injury is at present indirect. The importance of hypertrophy as a contributing factor to the progression of nonimmunologic glomerular injury is suggested by several lines of evidence. Hypertrophy, with increase in glomerular size and caliber of capillary loops, may amplify the effect of increased PGC by further intensifying the tension and mechanical stress on all elements of the capillary wall.(ABSTRACT TRUNCATED AT 400 WORDS)