Glomerular and tubular adaptive responses to acute nephron loss in the rat. Effect of prostaglandin synthesis inhibition.

These studies, using in vivo micropuncture techniques in the Munich-Wistar rat, document the magnitude of changes in glomerular and tubular function and structure 24 h after approximately 75% nephron loss (Nx) and compared these results with those obtained in sham-operated rats. The contribution of either nephron hypertrophy or renal prostaglandin to these adjustments in nephron function was also explored. After acute Nx, single nephron GFR (SNGFR) was increased, on average by approximately 30%, due primarily to glomerular hyperperfusion and hypertension. The approximately 45% reduction in preglomerular and the constancy in postglomerular vascular resistances was entirely responsible for these adaptations. Although increases in fluid reabsorption in proximal convoluted tubules correlated closely with increase in SNGFR, the fractional fluid reabsorption between late proximal and early distal tubular segments was depressed. Nephron hypertrophy could not be substantiated based on either measurements of protein content in renal tissue homogenates or morphometric analysis of proximal convoluted tubules. However, acute Nx was associated with increased urinary excretory rates per functional nephron for 6-keto-PGF1 alpha and TXB2. Prostaglandin synthesis inhibition did not affect function in control nephrons, but this maneuver was associated with normalization of glomerular and tubular function in remnant nephrons. The results suggest that enhanced synthesis of cyclooxygenase-dependent products is one of the earliest responses to Nx, and even before hypertrophy the pathophysiologic effects of prostaglandin may be important contributors to the adaptations in remnant nephron function.

Failure of postnatal adaptation of the pulmonary circulation after chronic intrauterine pulmonary hypertension in fetal lambs.

To determine the effects of chronic intrauterine pulmonary hypertension on the perinatal pulmonary circulation, we induced chronic elevations of pulmonary artery pressure in 24 late-gestation fetal lambs by maintaining partial compression of the ductus arteriosus with an inflatable vascular occluder. Pulmonary artery pressure was increased from 44 +/- 1 to 62 +/- 3 mmHg for 3-14 d. Although left pulmonary artery blood flow initially increased during acute partial ductus compression, the increase in flow was not sustained during chronic ductus compression despite persistent elevations of pulmonary artery pressure (P less than 0.01). Chronic hypertension decreased the slope of the pressure-flow relationship from 3.4 +/- 0.3 (initial) to 0.9 +/- 0.1 ml/min per mmHg, and blunted the fetal pulmonary vascular response to small increases in PO2 (P less than 0.0001). Pulmonary hypertension for greater than 8 d increased the wall thickness of small pulmonary arteries (P less than 0.001). Compared with controls, hypertensive animals had higher pulmonary artery pressure, lower pulmonary blood flow, and predominant right-to-left ductus shunting after cesarean-section delivery (P less than 0.0001). We conclude that chronic pulmonary hypertension in utero, in the absence of hypoxemia or sustained increases in blood flow, causes abnormal fetal pulmonary vasoreactivity, structural remodeling, and the failure to achieve the normal decline in pulmonary resistance at birth.

In vitro and in vivo protective effect of atriopeptin III on ischemic acute renal failure.

The effect of atriopeptin III (AP-III) on ameliorate ischemic acute renal failure was first examined in the isolated perfused kidney. Isolated rat kidneys were clamped for 1 h and reperfused for 30 min without therapy and then perfused with either 0 (control) or 100 micrograms/dl AP-III. In this system AP-III significantly improved renal plasma flow (39.6 +/- 2.4 vs. 32.2 +/- 2.1 ml/min per g; P less than 0.05) inulin clearance (182.6 +/- 49.2 vs. 24.6 +/- 6.2 microliters/min per g; P less than 0.05), urine flow (52.9 +/- 12.1 vs. 7.1 +/- 0.8 microliters/min per g, P less than 0.01), and net tubular sodium reabsorption (21.2 +/- 6.6 vs. 2.9 +/- 0.9 mumol/min per g, P less than 0.05) as compared with control. A second series of in vivo studies experiments were performed using 1 h of bilateral renal artery clamping followed by an intravenous infusion of either saline alone (control) or AP-III (0.20 microgram/kg per min) for 60 min. The results demonstrated that inulin clearance (244.4 +/- 25.1 vs. 15.8 +/- 8.2 microliters/min per 100 g; P less than 0.01), urine flow (23.1 +/- 5.9 vs. 1.1 +/- 0.5 microliters/min per 100 g; P less than 0.01), and net tubular sodium reabsorption (38.9 +/- 4.7 vs. 4.3 +/- 1.6 mumol/min per 100 g; P less than 0.01) were significantly higher in AP-III-treated rats than controls during the hour of AP-III infusion. In 1 h posttreatment study this significant protective effect of AP-III was documented to persist. In more chronic studies animals treated acutely with AP-III had lower serum creatinine concentration at 24 h (1.8 +/- 0.3 vs. 3.3 +/- 0.4 mg/dl; P less than 0.01) and 48 (1.0 +/- 0.2 vs. 2.4 +/- 4.0 mg/dl; P less than 0.01) after the 60 min of ischemia than controls. Renal adenosine triphosphate regeneration as assessed by P-31 nuclear magnetic resonance during reflow was also significantly improved in AP-III-treated animals at 1 h (3.03 +/- 0.30 vs. 1.45 +/- 0.40 mumol/g dry wt; P less than 0.05) and 2 h (3.98 +/- 0.46 vs. 1.80 +/- 0.05 mumol/g dry wt; P less than 0.01) or reflow as compared with control rats. Thus, AP-III significantly ameliorates ischemic acute renal failure both in vitro and in vivo in the rat.

Transgenic mice with expression of elevated levels of copper-zinc superoxide dismutase in the lungs are resistant to pulmonary oxygen toxicity.

To test the hypothesis that increases in lung superoxide dismutase can cause tolerance to pulmonary oxygen toxicity, we studied transgenic mice which constitutively express elevated levels of the human copper-zinc SOD (CuZnSOD). Upon exposure to hyperoxia (greater than 99% O2, 630 torr) the transgenic CuZnSOD mice showed increased survival, decreased morphologic evidence of lung damage such as edema and hyaline membrane formation, and reduction in the number of lung neutrophils. During continuous exposure to oxygen, both control and transgenic animals who successfully adapted to hyperoxia showed increased activity of lung antioxidant enzymes such as glutathione peroxidase (GPX), glutathione reductase (GR), and glucose-6-phosphate dehydrogenase (G6PD), whereas superoxide dismutase activity remained unchanged. The results show that expression of elevated levels of CuZnSOD decreases pulmonary oxygen toxicity and associated histologic damage and mortality.

31P nuclear magnetic resonance study of renal allograft rejection in the rat.

Phosphorus (31P) nuclear magnetic resonance (NMR) spectroscopy was used to serially evaluate heterotopic renal allograft rejection in the rat. Renal allografts transplanted to the groin of recipient animals were studied using a 1.89 Tesla horizontal bore magnet. The relative intracellular concentrations of phosphorus metabolites such as adenosine triphosphate and inorganic phosphate as well as intracellular pH were determined by 31P NMR on days 4, 7, 10, and 14 following transplantation across a major histocompatibility mismatch. Recipient rats chosen to be rejectors received no immunosuppression while animals chosen to be nonrejectors received cyclosporine during the first 7 days following transplantation. By day 7, all rejector rats could be distinguished from nonrejector rats by their higher relative concentration of inorganic phosphate and their lower relative concentration of adenosine triphosphate. These NMR findings correlated with histologic findings of renal infarction probably related to vascular rejection in the allografts. 31P NMR spectroscopy may have application as a noninvasive tool in the differential diagnosis of posttransplantation renal insufficiency.

Adenovirus infection of the renal allograft with sparing of pancreas graft function in the recipient of a combined kidney-pancreas transplant.

We report a case of adenovirus infection of the renal allograft in a combined kidney/pancreas transplant recipient. The clinical presentation was renal allograft failure, which eventually reversed. The pancreatic graft function remained stable. A renal biopsy showed massive tubular necrosis associated with a prominent granulomatous reaction. The process had a striking regional distribution within the kidney with the injury and inflammation limited to the outer medulla. Adenovirus type 11 was isolated from renal tissue by culture, and adenovirus was demonstrated by immunofluorescence and electron microscopy in the kidney biopsy. Immunosuppression may result in unusual patterns of response to infectious agents. This case demonstrated tropism of the adenovirus to only selected tubules within the kidney, with sparing of other organ function including, specifically, the pancreas allograft. The differential diagnosis of a granulomatous reaction in the transplant kidney must be expanded to include viral infection, in particular, adenovirus.

The pathology of chronic renal ischemia.

Chronic ischemia may cause end stage renal disease, especially in older patients with atherosclerotic renal artery stenosis. Examining the pathology of the ischemic kidney is a fundamental first step toward understanding the mechanisms of this injury. In experimental renal hypoperfusion, there is evidence of a mixture of adaptive responses, tubular and endothelial cell damage and repair events. These processes are reflected in a wide spectrum of morphological changes that include atrophy, focal necrosis, epithelial regeneration, apoptosis, inflammation, interstitial fibrosis, and thrombosis. The most severe damage is seen in the outer medulla, a region with marginal oxygenation even in normal circumstances. In the usual clinical case, the effects of aging, pre-existent hypertension, and the process of atherosclerosis further complicate the pathological picture. Lesions related to these factors include arteriosclerosis, athero-emboli, various types of glomerulosclerosis, and severe tubulointerstitial damage leading to "atubular glomeruli" and regional cortical scarring (nephrosclerosis). In this article, some mechanisms determining the varied and complex pathological findings that may be observed in individual cases are outlined.

Marginating neutrophils are reversibly adherent to normal lung endothelium.

Neutrophils have been implicated in the pathogenesis of several inflammatory lung disorders including asthma, emphysema, and adult respiratory distress syndrome. The precursors of these destructive cells are thought to be marginating neutrophils that, although intravascular, remain intimately associated with endothelium, resisting the shearing forces of flowing blood. The purposes of this study were (1) to examine a method for quantitating marginating lung neutrophils, (2) to assess the adherence of marginating neutrophils to normal lung endothelium, and (3) to determine the reversibility of neutrophil-endothelial cell adherence. Rats were anesthetized and ventilated, and their lungs were exposed through a median sternotomy. The left lung was tied off with blood in situ and the right lung was perfused intraarterially with colloid for 2 minutes. In separate experiments, both left and right lungs were perfused intraarterially with colloid for 25 minutes. Myeloperoxidase, a neutrophil granule enzyme, was related to lung neutrophils. Dithionite-sensitive optical density (DSOD) was related to lung hemoglobin. Marginating lung neutrophils were quantitated by measuring the peroxidase activity of normal blood-perfused lung (myeloperoxidase assay) and subtracting from it the fraction of activity corresponding to the lung blood content (DSOD). The marginating neutrophil pool was identified by 2.1 units myeloperoxidase (5 x 10(6) neutrophils) per gm wet lung. Although the marginating pool was depleted by 54% during 2 minutes of lung colloid perfusion, lung erythrocytes (DSOD) were decreased by a significantly greater 93% (p less than 0.05). Lungs perfused with colloid for 25 minutes had negligible remaining myeloperoxidase activity. We conclude that (1) marginating lung neutrophils can be quantitated with the myeloperoxidase and DSOD assays, (2) marginating neutrophils are relatively adherent to normal lung endothelium compared with intravascular erythrocytes, and (3) the adherence of marginating neutrophils is fully reversible.

Liposome-entrapped PGE1 posttreatment decreases IL-1 alpha-induced neutrophil accumulation and lung leak in rats.

We found that treatment with liposome-entrapped prostaglandin E1 (Lip-PGE1), but not with empty liposomes and/or free PGE1, decreased the leak of intravascularly administered 125I-labeled albumin into lungs of rats given interleukin-1 alpha (IL-1 alpha) intratracheally. Lip-PGE1 treatment also decreased lung myeloperoxidase activity, lung lavage neutrophil increases, and lung histological abnormalities found in rats given IL-1 alpha intratracheally. Interestingly, decreased lung leak and lung neutrophil accumulation occurred when Lip-PGE1 was given intravenously 2.5 h after, but not immediately before, intratracheal IL-1 alpha administration. When Lip-PGE1 treatment was given both before and 2.5 h after IL-1 alpha administration, lung leak was decreased to baseline levels. Lip-PGE1 treatment given 2.5 h after IL-1 alpha administration also decreased lung oxidized glutathione levels, which increased in rats given IL-1 alpha intratracheally. We conclude that postinsult treatment with Lip-PGE1 decreases lung leak, neutrophil recruitment, and oxidative responses in lungs of rats given IL-1 alpha intratracheally.

Xanthine oxidase promotes neutrophil sequestration but not injury in hyperoxic lungs.

Neutrophil accumulation in alveolar spaces is a conspicuous finding in hyperoxia-exposed lungs. We hypothesized that xanthine oxidase (XO)-derived oxidants contribute to retention of neutrophils in hyperoxic lungs. Rats were subjected to normobaric hyperoxia (100% O2) for 48 h, and lungs were assessed for neutrophil sequestration (morphometry and lavage cell counts) and injury (lavage albumin levels and lung weights). In rats exposed to hyperoxia, we found increased (P < 0.05) lung neutrophil retention, lavage albumin levels, and lung weights compared with normoxia-exposed control rats. Suppression of XO activity by pretreatment with allopurinol decreased (P < 0.05) lung neutrophil retention but increased (P < 0.05) lavage albumin concentrations and lung weights in hyperoxic rats. Allopurinol treatment had no effect (P > 0.05) on the numbers of macrophages or lymphocytes recoverable by lung lavage. Depletion of XO activity by an independent method, tungsten feeding, also decreased (P < 0.05) lung lavage neutrophil counts and increased (P < 0.05) lavage albumin concentrations. We conclude that XO may be involved in lung neutrophil retention but not lung injury during exposure to hyperoxia.

Cutaneous macroglobulinosis. A case report with unique ultrastructural findings.

BACKGROUND: Cutaneous macroglobulinosis is a rare cutaneous manifestation of Waldenström's macroglobulinemia. Lesions result from the direct deposition of macroglobulin in the skin and have been called IgM storage papules. A case of cutaneous macroglobulinosis with unique ultrastructural findings was studied. OBSERVATIONS: Cutaneous macroglobulinosis is characterized by multiple flesh-colored papules on extensor skin surfaces. Histologically, there are dermal collections of eosinophilic hyaline material, simulating amyloid. The material is positive on periodic acid-Schiff staining. Amyloid stains are negative or equivocal. Electron microscopy reveals thick, nonbranching, 56-nm-wide, linear material with cross striations at 12-nm intervals. These ultrastructural findings differ from the three previously reported cases. CONCLUSIONS: Cutaneous macroglobulinosis may be a rare presenting sign of Waldenström's macroglobulinemia. Deposits of macroglobulin in the skin result in a histologic picture that greatly resembles amyloid. Histochemical stains, direct immunofluorescence microscopy, and electron microscopy are useful tools that enable accurate diagnosis and help to distinguish cutaneous macroglobulinosis from other deposition disorders.

Interleukin-1 treatment increases neutrophils but not antioxidant enzyme activity or resistance to ischemia-reperfusion injury in rat kidneys.

Hearts from rats treated with interleukin-1 (IL-1) intraperitoneally developed a rapid (6 h after IL-1), transient increase in neutrophils, tissue hydrogen peroxide (H2O2), and oxidized glutathione (GSSG) levels, and a subsequent (36 h after IL-1) increase in myocardial glucose-6-phosphate dehydrogenase (G6PD) activity and tolerance to ischemia-reperfusion. In the present investigation, we found that rats treated similarly with IL-1 had increased numbers of neutrophils in their kidneys, which were comparable to myocardial neutrophil increases, but did not develop increased renal tissue H2O2 or GSSG levels acutely (6 h after IL-1) or increased G6PD activity or resistance to ischemia-reperfusion injury later (36 h after IL-1). Our findings indicate that IL-1 treatment increased neutrophil accumulation in rat kidneys but did not increase oxidative stress, antioxidant enzyme activity, or resistance to ischemia-reperfusion injury. We conclude that organ-to-organ differences exist with respect to IL-1-induced tolerance.

Differential susceptibility to gentamicin toxicity within the proximal convoluted tubule.

The proximal convoluted tubule (PCT) is the major target for injury in gentamicin nephrotoxicity but the necrosis is often patchy and focal. The PCT is structurally, functionally, and metabolically heterogeneous, and the possibility of differential vulnerability to gentamicin-induced necrosis based on this heterogeneity has not been examined. A quantitative analysis comparing the extent of necrosis in the initial portion of the PCT (S1) to that in the more distal PCT (S2) and comparing necrosis in the PCT of superficial nephrons to that in juxtamedullary nephrons was done in rats after eight daily intraperitoneal doses of 100 mg gentamicin/kg rat weight. The results indicate that the PCT of superficial nephrons are more susceptible to necrosis than the PCT of juxtamedullary nephrons and that the initial S1 segment even in the superficial nephrons is remarkably resistant to injury. These findings suggest that some aspects of the functional or metabolic heterogeneity within the PCT may be related to either differential rates of uptake of the drug or to differences in intrinsic susceptibility to its toxic effects.

Adenine nucleotides, transport activity and hypoxic necrosis in the thick ascending limb of Henle.

Thick ascending limb of Henle (TAL) necrosis in the isolated perfused kidney is an important model of renal hypoxia, but physiologic and metabolic correlation with this morphologic damage has been inadequate. More precise estimation of TAL adenine nucleotides in this model was obtained in the present study by high pressure liquid chromatography analysis of biopsy samples from the inner stripe of the outer medulla during perfusion. The inner stripe, which is the zone where TAL are concentrated, showed ATP depletion and low adenylate energy charge (AEC) early in perfusion prior to the appearance of TAL necrosis. Free water clearance (CH2O) was used as an estimate of TAL transport activity; the CH2O observed during 90 minute perfusions was found to be predictive of the extent of TAL necrosis in each experiment. The results support the idea that there is significant medullary hypoxia in the isolated perfused kidney and that TAL solute transport is a determinant of injury in this model. In further studies, the effects of ouabain (10(-3) M), furosemide (10(-4) M) or acidosis (pH 7.0 rather than the usual pH 7.4) on TAL transport activity and adenine nucleotide levels were compared. All three maneuvers have been shown previously to reduce TAL injury in the isolated perfused kidney. Addition of ouabain or furosemide reduced CH2O and TAL necrosis in parallel while acidosis had no effect on CH2O during perfusion. Both ouabain and furosemide attenuated ATP depletion and resulted in higher AEC while acidosis had no effect on these indices of cellular hypoxia. Therefore, the mechanism of cytoprotection by acidosis appears distinct from that of ouabain or furosemide.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium and acidosis in renal hypoxia.

The effects of lowering extracellular calcium concentration on hypoxic injury in the thick ascending limb of Henle (TAL) were studied in the isolated perfused rat kidney. At standard conditions of pH 7.4 and total perfusate calcium 1.9 mM, widespread TAL necrosis results from the combined effects of low medullary O2 delivery and the demands of solute transport activity. Reducing calcium to 0.5 or 0.1 mM, effectively prevented TAL membrane fragmentation. This cytoprotection was not accompanied by improved O2 delivery or by any consistent effects on renal physiology (glomerular filtration rate, sodium reabsorption, free water clearance or O2 consumption) that might have suggested that the mechanism was reduced O2 demand. In addition, the medullary ATP depletion which characteristically precedes TAL necrosis was not reversed. Finally, reduced perfusate calcium also markedly decreased TAL damage in an alternative model of hypoxia-like injury caused by a respiratory uncoupler. In aggregate, these findings indicate that reducing extracellular calcium does not prevent hypoxia itself, but rather disrupts the mechanism of its effects on cell integrity. The relationship of H+ and Ca2+ in the pathogenesis of hypoxic TAL injury was also studied. Lowering media pH to 7.0 reduced TAL damage but this cytoprotection was overcome by increasing media calcium concentration. Furthermore, with more severe acidosis (media pH 6.5 or 6.0), progressively greater perfusate calcium concentrations were required to reproduce severe TAL damage. These results indicate that extracellular calcium promotes the development of hypoxic TAL necrosis and that the cytoprotective effect of acidosis in hypoxia may be to counteract the calcium-dependent mechanism of injury.

Angiotensin II control of the renal microcirculation in rats with reduced renal mass.

It has been suggested that angiotensin II (ANG II) activation after renal ablation contributes to the altered glomerular dynamics and proteinuria that characterizes this model of chronic renal failure. In the present study, male Munich-Wistar rats underwent 75% renal ablation (Nx group). Two weeks later, micropuncture studies were performed in sham-operated rats (sham group) and Nx group rats during intravenous infusion of either a vehicle or two ANG II inhibitors, namely [Sar1, Ala8]ANG II or MK-421 administered at a rate of 0.3 and 1 mg.kg body wt-1.h-1, respectively. Acute ANG II inhibition in sham group had no effect on mean arterial pressure (MAP), glomerular dynamics, or proteinuria. In contrast, in Nx group ANG II inhibition lessened glomerular hypertension (from 64.7 +/- 1.0 to 55.4 +/- 1.7 mmHg, P less than 0.0001) the result of postglomerular vasodilation (P less than 0.01), normalized the glomerular ultrafiltration coefficient (from 0.038 +/- 0.002 to 0.005 +/- 0.002 nl.s-1.mmHg-1, P less than 0.0001), and attenuated proteinuria (from 42.1 +/- 6.5 to 28.1 +/- 5.4 micrograms/min, P less than 0.01). MAP, single-nephron GFR and plasma flow were unaffected. These results suggest that ANG II activity is enhanced in nephrectomy, contributing in a major way to altered glomerular dynamics and proteinuria.

Mild ischemia predisposes the S3 segment to gentamicin toxicity.

The purpose of these studies was to determine if a functionally insignificant ischemic insult, occurring prior to gentamicin administration, enhanced gentamicin nephrotoxicity. Bilateral renal pedicle clamp studies demonstrated that 15 minutes of ischemia did not increase the plasma creatinine yet markedly enhanced gentamicin nephrotoxicity. Further studies, in uninephrectomized rats, demonstrated that following fifteen minutes of renal ischemia and four hours of reperfusion inulin clearance, FENa+ and cellular morphology were normal. This model, therefore, was used in all subsequent studies. While the plasma creatinine concentrations were normal 24 hours following 15 minutes of ischemia and only slightly increased following gentamicin administration (100 mg/kg, i.p.) gentamicin administered four hours following 15 minutes of renal ischemia resulted in significantly increased 24-hour plasma creatinine values. Light microscopic quantitation of tissue injury, performed 24 hours following experimental manipulation, was notable for S3 segment damage in the ischemia plus gentamicin group. This was not observed in either the ischemia group or the sham operated gentamicin group. Cortical gentamicin levels were elevated in the ischemia plus gentamicin group, despite similar plasma gentamicin half-lives. However, the elevation in cortical gentamicin levels was dissociated from the enhanced nephrotoxicity seen following mild ischemic injury. Taken together these data indicate that mild renal ischemia, occurring prior to gentamicin administration, greatly enhanced gentamicin nephrotoxicity with the greatest damage occurring to S3 cells.

Neutrophils accentuate ischemia-reperfusion injury in isolated perfused rat kidneys.

The contribution of neutrophils to reperfusion injury after ischemia is not known. To determine the effect of neutrophils on the function of ischemic kidneys, we added purified human neutrophils during perfusion of isolated ischemic or nonischemic rat kidneys. Reperfusion of ischemic kidneys with neutrophils caused a distinct morphological lesion of vascular endothelial and smooth muscle cells and more functional injury than reperfusion with buffered albumin alone; with neutrophils, glomerular filtration rate (GFR) was 113 +/- 7 microliter.min-1.g-1, tubular sodium reabsorption (TNa) was 72 +/- 2%; without neutrophils, GFR was 222 +/- 18 microliter.min-1.g-1; TNa was 90 +/- 2%; both P less than 0.01 vs. reperfusion with neutrophils. In contrast, addition of neutrophils did not injure control kidneys, unless the neutrophil activator, phorbol myristate acetate, was also added. Two experiments suggested that O2 metabolites contributed to neutrophil-mediated injury to ischemic kidneys. First, reperfusion of ischemic kidneys with O2 metabolite-deficient neutrophils from a patient with chronic granulomatous disease did not cause more injury than reperfusion with buffered albumin alone. Second, simultaneous addition of the O2 metabolite scavenger, catalase, prevented the GFR and TNa decreases caused by neutrophils but did not decrease injury in the absence of neutrophils. We conclude that neutrophils by an O2 metabolite-dependent mechanism contribute to ischemia-reperfusion injury in the isolated perfused kidney.

Acidosis and hypoxic medullary injury in the isolated perfused kidney.

The effects of acidosis on renal function and morphology were examined in the isolated perfused rat kidney (IPK). Kidneys were perfused with oxygenated Krebs-Henseleit-albumin medium for 60 minutes at pH 7.4 or pH 7.0. At the lower pH, GFR was reduced by 25%, TRNa by 32% and oxygen consumption by 41% as compared to perfusion at pH 7.4 (all P less than 0.05). In addition, the usual hypoxic injury observed in the medullary thick ascending limb of the Loop of Henle (TAL) in the IPK at pH 7.4 (consisting of nuclear pyknosis and focal fragmentation necrosis) was reduced by acidosis from 62% to 14% of tubules involved (P less than 0.005). This cytoprotection was not the result of improved oxygenation since O2 delivery was actually slighty reduced at pH 7.0 compared to pH 7.4. Furthermore, acidosis was protective even after perfusion with non-oxygenated media (42% tubules damaged at pH 7.0 vs. 95% of tubules damaged at pH 7.4; P less than 0.01), making it very unlikely that the effect of acidosis is to improve TAL oxygenation. Since previous studies indicate that the TAL lesion is transport dependent and prevented in the non-filtering kidney, it was possible that the decrease in GFR associated with acidosis could account for decreased injury. The GFR was manipulated by alterations in perfusion pressure or albumin concentration, and no consistent relationship between the extent of injury and GFR could be shown at either pH over a wide range of GFR values. Therefore, acidosis protected the TAL from hypoxic injury by a mechanism apparently independent of oxygen or solute delivery.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential responsiveness of proximal tubule segments to metabolic inhibitors in the isolated perfused rat kidney.

Rat kidneys were perfused for 90 minutes with cyanide, rotenone, antimycin, 2-deoxyglucose, or combinations of rotenone or antimycin with 2-deoxyglucose in oxygenated Krebs-albumin medium. Following perfusion, proximal tubule injury was evaluated by light microscopy. The types of lesions seen were similar to those previously reported after hypoxic perfusion and included brush border clubbing/mitochondrial swelling in S1 and S2 and cytoplasmic edema or cell fragmentation in S3. This finding supports the contention that these lesions represent characteristic responses of these segment types and that the S3 response differs from that in S1 and S2. S1 appeared most vulnerable to low dose cyanide or inhibition of mitochondrial electron transport (rotenone, antimycin). Inhibition of glycolysis (2-deoxyglucose) only produced injury in S2 tubules. With high dose cyanide or a combination of 2-deoxyglucose with either rotenone or antimycin, there was diffuse proximal tubule damage. Thus S3 appeared more resistant than the convoluted tubular segments to both inhibition of glycolysis and to inhibition of mitochondrial electron transport. This finding stands in contrast to the selective vulnerability of the S3 segment in ischemic renal injury.