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Biomedical subjects

M Brezis

Publications and source records attributed to M Brezis.

At least 91 records · Page 5Linked to original sources
PubMed1991

Effects of adenosine on intrarenal oxygenation.

Although generally a vasodilator, adenosine vasoconstricts cortical vessels in the kidney, reduces glomerular filtration rate (GFR), and increases medullary blood flow, effects likely to improve the medullary O2 deficiency characteristic of mammalian kidneys. To evaluate a possible role of adenosine in medullary O2 balance, we investigated the effect of adenosine upon cortical and medullary tissue PO2. Adenosine was infused into renal interstitium through chronically implanted capsules. Cortical and medullary PO2 were measured using sensitive Clark-type O2 microelectrodes inserted into kidneys of anesthetized rats at the respective depths of 1.8 and 3.7 mm. Infusion of adenosine (0.1-0.5 mumol/min) increased medullary PO2 from 17 +/- 3 (SE) to 40 +/- 5 mmHG (P less than 0.001) and decreased cortical PO2 from 64 +/- 4 to 47 +/- 3 mmHg (P less than 0.001). After the infusion was stopped, PO2 returned to baseline at both sites. Coadministration of adenosine receptor antagonist 8-phenyltheophylline (0.01 mumol/min) prevented both cortical and medullary effects of adenosine. We concluded that adenosine could play an important protective and regulatory role in renal medullary O2 balance.

Adenosine↗
PubMed1991

Role of nitric oxide in renal medullary oxygenation. Studies in isolated and intact rat kidneys.

We investigated the role of the endothelial-derived relaxing factor nitric oxide (NO) in the homeostasis of O2 supply to the renal medulla, a region normally operating on the verge of hypoxia. Sensitive Clark-type O2 microelectrodes were inserted into renal cortex and medulla of anesthetized rats. The inhibitor of NO formation, L-NG-monomethylarginine (LNMMA), while increasing blood pressure and reducing renal blood flow, decreased medullary pO2 from 23 +/- 3 mmHg to 12 +/- 3 (P less than 0.001), with no change in the cortex. These responses were promptly reversed by L-arginine, which bypasses the LNMMA blockade. In isolated rat kidneys, LNMMA reduced perfusion flow without altering glomerular filtration rate, and augmented deep medullary hypoxic injury to thick ascending limbs from 68 to 90% of the tubules (P less than 0.02). These changes were prevented by L-arginine. Nitroprusside had a protective effect upon thick limb injury. Finally, in a previously reported model of radiocontrast nephropathy (1988. J. Clin. Invest. 82:401), LNMMA increased the severity of renal failure (final plasma creatinine from 2.3 +/- 2 mg% to 3.4 +/- 3, P less than 0.005) and the proportion of damaged thick limbs (from 24 +/- 6% to 53 +/- 9, P less than 0.01). Nitrovasodilatation may participate in the balance of renal medullary oxygenation and play an important role in the prevention of medullary hypoxic injury.

Acute Kidney Injury↗
PubMed1990

Hypercalcemic nephropathy: chronic disease with predominant medullary inner stripe injury.

Because of the recently observed augmentation of medullary hypoxic injury by calcium in isolated perfused rat kidneys (Kidney Int 34:186-194, 1988), renal morphology of chronic, prolonged hypercalcemia was investigated in vivo. Rats were treated with repeated injections of vitamin D2 (400,000 units/week) for two to eight weeks. Chronic elevation of plasma calcium from 2.1 to 2.8 mmol/liter (P less than 0.001) was associated by a fall in maximal urine osmolality with no change in glomerular filtration rate. The most significant morphological alterations occurred in the inner stripe of the outer medulla; these changes were characterized by a sequence of active injury with subsequent destruction and atrophy of the medullary thick ascending limbs, fibroblastic and lymphocytic infiltration, and secondary dilatation of collecting ducts. Similar changes occurred in the medullary rays. These alterations were accompanied by increased renal prostanoid production and a predisposition to acute kidney failure from indomethacin. Because of its selective occurrence in zones of poorest oxygen supply, this inner stripe injury may derive from vulnerability to hypoxia and may play a role in some chronic nephropathies.

Animals↗
PubMed1990

Chronic cyclosporine-induced nephropathy in the rat. A medullary ray and inner stripe injury.

Cyclosporine CsA nephrotoxicity was examined in male Sprague-Dawley rats with or without prior uninephrectomy, injected daily with 12.5 mg/kg CsA, and fed a salt-depleted or normal diet for 3-10 weeks. Control rats received the CsA vehicle. CsA induced a fall in creatinine clearance in salt-depleted rats, from 1.3 +/- 0.1 to 0.8 +/- 0.1 ml/min (P less than 0.001), and in normally fed rats from 1.8 +/- 0.2 to 1.0 +/- 0.2 ml/min (P less than 0.02). Vehicle treatment had no effect. The most striking morphologic changes were those of thick ascending limb cell atrophy with concomitant fibroblastic proliferation and collagen formation; these alterations were present in the inner stripe of the outer medulla and the medullary ray. The medullary-ray findings included S2-S3 degenerative changes as well and apparently correspond to the striped fibrosis described in human CsA nephropathy. The alterations were specific to the CsA group, progressive, and most severe in the salt-depleted, CsA-injected rats (on a scale of 0-4: 1.7 +/- 0.2 for medullary rays, and 2.0 +/- 0.2 for inner stripe, P less than 0.001). Morphologic changes predicted renal failure (r = 0.3, P less than 0.01 for cortical alterations, and r = 0.5, P less than 0.001 for medullary alterations). Prior uninephrectomy did not enhance these changes. Thus, chronic CsA administration impaired kidney function and induced morphologic alterations found in regions characterized by, and in nephron segments particularly vulnerable to, limited O2 availability. Salt depletion appears to accelerate the development of chronic CsA renal injury in the rat.

Animals↗
PubMed1990

Angiotensin II augments medullary hypoxia and predisposes to acute renal failure.

The effects of angiotensin II (AII) upon medullary hypoxic injury and kidney function were investigated in vitro and in vivo. Synthetic AII added to perfusate of isolated rat kidneys reduced perfusion flow from 48 +/- 2 ml min-1 (+/- SE) to 19 +/- 1 (P less than 0.001) without altering glomerular filtration rate (GFR), raising filtration fraction from 1% to 3% (P less than 0.001). AII-extended hypoxic injury to medullary thick ascending limbs (mTAL) from 66 +/- 4% of tubules to 79 +/- 3 (P less than 0.05) in correlation with filtration fraction (r = 0.8, P less than 0.001). Addition of indomethacin (10(-4) mol l-1) further extended medullary hypoxic damage to 89 +/- 2% of mTAL (P less than 0.001). Uninephrectomized rats kept in metabolic cages were given AII by continuous infusion (0.1-0.8 microgram min-1) and indomethacin (10 mg kg-1 day-1) for 24 h. Creatinine clearance declined from 1.3 +/- 0.1 ml min-1 to 0.6 +/- 0.06 (P less than 0.001). Morphological examination revealed either selective necrosis of mTAL (in 12 +/- 4% of tubules) or luminal collapse (in 63 +/- 8%). Both necrosis and collapse correlated inversely with creatinine clearance and with each other (r = -0.5, P less than 0.001), the latter correlation suggesting protection from hypoxic injury by cessation of solute delivery. By increasing filtration fraction and decreasing blood flow, AII decreases renal oxygen supply while maintaining oxygen consumption for solute reabsorption. AII may predispose to acute renal failure by augmenting medullary hypoxia.

Acute Kidney Injury↗
PubMed1990

Effects of perfusion pressure and renal flow upon albumin excretion in isolated perfused kidneys.

To explore the effects of renal hemodynamics upon urinary albumin excretion, sequential changes in perfusion pressure and/or flow were performed in isolated perfused rat kidneys. Elevation of perfusion pressure from 90 to 130 mm Hg increased renal flow from 48.9 +/- 1.1 to 54.3 +/- 1.4 ml/min and glomerular filtration rate (GFR) from 0.37 +/- 0.03 to 0.81 +/- 0.06 ml/min (p less than 0.001). Despite more than a doubling in GFR, albumin excretion remained unchanged (from 252 +/- 53 to 167 +/- 36 micrograms/min, p not significant), resulting in a decreased fractional clearance of albumin (theta) from 0.009 +/- 0.002 to 0.004 +/- 0.005 ml/min (p less than 0.01). To dissociate the effects of flow from those of pressure, angiotensin II was infused to decrease renal flow from 49.9 +/- 0.6 to 38.7 +/- 0.6 ml/min (p less than 0.001), while keeping perfusion pressure constant at 96 +/- 1 mm Hg. Although GFR was essentially unchanged (from 0.59 +/- 0.02 to 0.65 +/- 0.05 ml/min, p not significant), albumin excretion increased from 68 +/- 8 to 151 +/- 21 micrograms/min (p less than 0.001) and theta rose from 0.002 +/- 0.000 to 0.005 +/- 0.001 (p less than 0.02). Whole kidney hemodynamics acutely affect renal excretion of albumin in isolated kidneys.

Albuminuria↗
PubMed1990

Postpartum renal failure in systemic lupus erythematosus.

The present report describes an unusual association between postpartum renal failure and systemic lupus erythematosus. Two healty young women developed progressive renal failure several weeks after delivery accompanied by the presence in their serum of strongly reactive anti-nuclear antibodies and positive anti-DNA antibodies. In both cases kidney biopsy disclosed light and electron microscopy pictures typical of idiopathic postpartum renal failure, with multiple intravascular thrombi and no evidence of active lupus nephritis. Intrarenal microthrombi formation may represent a form of exacerbation of systemic lupus erythematosus after delivery. The early recognition of this syndrome may have therapeutic implications.

Acute Kidney Injury↗
PubMed1990

Relation of adenosine to medullary injury in the perfused rat kidney.

In isolated perfused rat kidneys the medullary thick ascending limb (mTAL) is uniquely vulnerable to cellular injury produced by its hypoxic milieu and exacerbated by active transport. Endogenous inhibitors of transport might therefore be expected to reduce cell injury. We studied the possible role of adenosine in altering mTAL damage in isolated rat kidneys perfused for 60 min. When adenosine deaminase was added to the recirculating perfusate in 8 experiments, severe damage to mTAL cells adjacent to the inner medulla was significantly exacerbated to involve 89.4 +/- 3% of them as compared to 74.9 +/- 4.7% in 9 controls (p less than 0.025). Similar results were obtained when 6-nitrobenzylthioinosine, which inhibits adenosine efflux from hypoxic cells, was added to the perfusion (n = 5, p less than 0.025). The addition of the adenosine analogue R(-)-phenylisopropyladenosine [R(-)-PIA] conferred protection, so that now only 12.5 +/- 2.5% of deep mTAL cells exhibited severe morphological damage (n = 7, p less than 0.005). The protective effect of R(-)-PIA was minimized by 8-phenyltheophylline, which blocks adenosine receptors. The S(+)-isomer of PIA was significantly less potent than R(-)-PIA in protecting against hypoxic injury. These results suggest that endogenous adenosine may play a role in modifying the injurious effects of anoxia on medullary cells, by inhibiting active transport.

Adenosine↗
PubMed1989

[Bilateral hydronephrosis and erythrocytosis].

A 36-year-old woman who developed extreme erythrocytosis following partial correction of severe bilateral hydronephrosis by bilateral ureterolithotomy is presented. Hydronephrosis appears to stimulate renal synthesis and release of erythropoietin. The mechanism could involve increase in medullary hypoxia by increased pressure of the renal pelvis on the medullary vasculature. This might be especially marked when the renal blood supply is compromised by concomitant atherosclerosis, as in this case.

Adult↗
PubMed1989

Anti-DNA antibodies bind directly to renal antigens and induce kidney dysfunction in the isolated perfused rat kidney.

The pathogenesis of SLE is commonly attributed to the deposition of circulating immune complexes consisting of DNA and anti-DNA autoantibodies. However, recent work has shown multiple cross-reactions between anti-DNA antibodies and a variety of cellular and extracellular Ag. To test the possibility that these antibodies interact directly with glomerular Ag and induce kidney dysfunction, we applied mouse and human anti-DNA IgG to the isolated perfused rat kidney. The NZB/NZW mouse monoclonal anti-DNA bound to glomerular Ag with a concomitant induction of proteinuria and a decrease in inulin clearance. The albumin excretion was 2301 +/- 734 micrograms/min at 160 min of perfusion, as compared with 85 +/- 21 micrograms/min in controls (p less than 0.001). The inulin clearance was reduced to 0.17 +/- 0.02 ml/min as compared with 0.28 +/- 0.09 ml/min in controls (p less than 0.05). Polyclonal anti-DNA IgG obtained from patients with lupus nephritis bound to rat glomeruli and induced albumin excretion of 542 +/- 217 micrograms/min at 160 min of perfusion, as compared with 163 +/- 77 micrograms/min in controls (p = NS). The addition of plasma as a source of C to the human IgG increased the proteinuria markedly (albumin excretion of 1115 +/- 195 micrograms/min at 160 min of perfusion, p less than 0.02), probably due to C activation. Preincubation of the reactive mouse and human IgG with DNA completely abolished their binding to renal tissue and its physiologic consequences. These results suggest that direct binding of anti-DNA antibodies to renal Ag may play an important role in the induction of lupus nephritis.

Adolescent↗
PubMed1989

Polyethylene glycol effect on the oxygenated and hypoxic isolated perfused rat kidney.

Polyethylene glycol protects against O2 deprivation after clamping of the renal artery or norepinephrine infusion and in hypoxic primary cell culture. Isolated perfused kidneys under hypoxic conditions develop morphological alterations in all segments of the proximal tubule and medullary thick ascending limb. In an attempt to ameliorate the effect of hypoxia, rat kidneys were perfused for 90 min with regularly oxygenated (95% O2 + 5% CO2) or hypoxic perfusate (95% N2 + CO2) supplemented with 8-12% polyethylene glycol (MW approximately 8000). In oxygenated and hypoxic kidneys, polyethylene glycol produced similar changes in S1-S2 segments consisting of reduction of cell thickness and organelle compaction with internalization of brush border into the tubulo-vesicular system. In the S3 segment, the cellular volume loss was more limited; the brush border was transformed to membranous whorls and the cytoplasm contained large, irregular, clear zones. Mitochondrial swelling was pronounced in the hypoxic proximal tubules. Polyethylene glycol quantitatively increased and emphasized the damage in the medullary thick ascending limb. Inclusion of 10(-2) M ouabain preserved the medullary thick ascending limb from hypoxic injury and polyethylene glycol had no effect on this undamaged epithelium. Thus, polyethylene glycol affects renal tubules on the basis of their known water permeability and does not protect against but rather worsens hypoxic injury in the medullary thick ascending limb.

Animals↗
PubMed1989

The vulnerability of the thin descending limbs of Henle's loop in the isolated perfused rat kidney.

In the isolated rat kidney perfused without erythrocytes, the medullary thick ascending limb shows extensive injury. Damage to the thin limbs of Henle's loop has been mentioned only briefly. Thin limbs were examined in the isolated perfused kidney under a variety of conditions that alter oxygenation and active transport in the medulla and are known to affect injury to the medullary thick ascending limb. The thin descending limbs of short loops were preserved in all experimental groups, but those of the long loop showed necrosis that was restricted to the proximal portion, where the epithelium is more complex. In oxygenated kidneys, necrosis involved 41% +/- 5% (mean +/- SE) of the medullary thick ascending limbs and 10% +/- 3% of the proximal portion of long loops of thin descending limbs. Under hypoxic conditions, necrosis involved 90% +/- 3% of the medullary thick ascending limbs and 70% +/- 5% of the proximal portion of long loops of thin descending limbs (P less than 0.0001 compared with oxygenated kidneys). Ouabain and absence of filtration completely prevented necrosis of both nephron segments. Thus, the proximal portions of long loops of thin descending limbs, in resemblance to medullary thick ascending limbs, are especially susceptible to transport-dependent hypoxic injury.

Animals↗