Ultrapure polymerized bovine hemoglobin improves structural and functional integrity of the isolated perfused rat kidney.

Since it became evident that organ dysfunctions after acute hemolysis are not induced by hemoglobin per se, but by stroma-contaminated hemoglobin, solutions of ultrapure stroma-free hemoglobins were regarded to be possible substitutes for blood in transfusion medicine. We tested one of the recently developed modified bovine hemoglobins (Ultrapure polymerized bovine hemoglobin 1; UPPBHb1) in the isolated perfused rat kidney (IPRK) model, using a recirculating system. Control kidneys were perfused with a substrate-enriched Ringer solution containing hydroxyethyl starch (HES) to produce isoncotic conditions. In the experimental group HES was substituted in part by UPPBHb1 (34 g/l). For determination of functional parameters, the kidneys were perfused for 180 min. A separate set of kidneys of both groups was perfusion fixed after 80 min of perfusion which is the period of optimal function. Light and electron microscopic analysis revealed major alterations only for the outer medulla of HES kidneys. Only these suffered from a considerable extent of proximal tubular S3 damage, exhibiting condensed tubular epithelia. In the inner stripe of the outer medulla, which is the zone of greatest sensitivity to damage in the isolated perfused kidney, severe hydropic degeneration, cell detachment, and necrotic destruction of the medullary thick ascending limb were seen in the HES-perfused group, too. In the UPPBHb1 group, the medullary thick ascending limb was well preserved, and S3 showed only a minor degree of damage. UPPBHB1 kidneys were further characterized by the occurrence of intracapillary and interstitial precipitates of UPPBHb1 in inner stripe of the outer medulla and inner medulla. The glomerular filtration rate was significantly higher in UPPBHb1-perfused kidneys (870 +/- 80 vs. 630 +/- 55 microliters/min/g kidney weight for HES). Absolute reabsorption of sodium paralleled the behavior of the glomerular filtration rate. The values for renal perfusate flow and urinary flow rate did not differ significantly between both groups. Renal autoregulation was better preserved in UPPBHb1-perfused kidneys (74 +/- 6% of full autoregulatory response) than in HES-perfused controls (42 +/- 4%). Our results suggest that perfusion of isolated rat kidneys with UPPBHb1 improves kidney function and morphology, providing better oxygenation than in control kidneys. UPPBHb1 does not exert additional nephrotoxic effects on the IPRK that will exceed the noxious potential of the method itself. Thus, it must be concluded that UPPBHb1 may be an oxyphoretic blood substitute with nephroprotective characteristics when compared with nonoxyphoretic substitutes. At least, UPPBHb1 seems to be a promising candidate as oxyphoretic additive to perfusates for the IPRK model.

Ultrapure polymerized bovine hemoglobin (UPPBHb) improves integrity of the isolated perfused rat kidney (IPRK): effects on function and structure.

To test the oxyphoretic properties and potential nephrotoxic side-effects of polymerized hemoglobin solutions, isolated rat kidneys were perfused in a recirculating system for 180 min. Group I was perfused with a substrate enriched Ringer solution containing hydroxyethylstarch (HES) to produce isoncotic conditions. In group II HES was substituted in part by UPPBHb (34 g/l) with a high portion of low molecular weight molecules (= UPPBHb1). In group III 34 g/l of UPPBHb containing an increased fraction of high molecular weight polymers (= UPPBHb2) was used. Only UPPBHb2-perfused kidneys showed a reduced renal perfusate flow (RPF, 13.3 +/- 1.1 ml/min g kw), when compared to HES-perfused controls (15.5 +/- 0.8) and UPPBHb1 (15.1 +/- 1.2). Glomerular filtration rate (GFR) was significantly higher in UPPBHb1-perfused kidneys (902 +/- 107 vs 633 +/- 55 microliters/min g kw for HES). This difference became even more pronounced in the third hour of perfusion (474 +/- 125 vs. 103 +/- 33). In contrast, UPPBHb2 produced low initial GFR levels of 385 +/- 25, which had only a minor tendency to decline with time. Parallel to GFR, absolute reabsorption of sodium (TNa) andoxygen consumption (QO2) showed values of 110 +/- 16 and 5.46 +/- 0.33 mumol/min g kw in UPPBHb1-kidneys vs 83 +/- 6 and 5.09 +/- 0.27 in controls and vs 53 +/- 4 and 3.66 +/- 0.12 in UPPBHb2-kidneys. Fractional excretion of sodium (FENa), of potassium (FEK), and of water (FEH2O) in UPPBHb1 and UPPBHb2-perfused kidneys were not significantly different from HES-perfused controls at any time of perfusion. Urinary flow rate (UFR) was similar in UPPBHb1- and HES-kidneys. Nevertheless, control kidneys tended to render oliguric during the third hour of perfusion (UFR 19.9 +/- 4.1 microliters/min g kw), whereas UPPBHb1 preserved urinary flow in a better way (83.7 +/- 32.4). UFR of UPPBHb2-kidneys was significantly reduced initially (30.2 +/- 5.1 vs. 105 +/- 33 for HES), but increased steadily up to 67 +/- 23. In the UPPBHb1 and HES group, all functional parameters determined declined dramatically within the third hour of perfusion, whereas UPPBHb2 produced functional stability. The in vivo reaction pattern of renal autoregulation was better preserved in UPPBHb-perfused kidneys than in HES-perfused controls: 74 +/- 6 vs. 59 +/- 5 vs. 42 +/- 4% (of full autoregulatory response) for UPPBHb1, UPPBHb2, and HES kidneys, respectively. Light- and electron microscopic analysis revealed major alterations only for the outer medulla of HES-kidneys.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro nephrotoxicity of Russell's viper venom.

To assess direct nephrotoxicity of Russell's viper venom (RVV; Daboia russelii siamensis), isolated rat kidneys were perfused in single pass for 120 min. Ten micrograms/ml and 100 micrograms/ml RVV were administered 60 minutes and 80 minutes, respectively, after starting the perfusion. Furthermore, cultured mesangial cells and renal epithelial LLC-PK1 and MDCK cells were exposed to RVV (100 to 1000 micrograms/ml) for 5 minutes up to 48 hours. The IPRK dose-dependently exhibited reductions of renal perfusate flow (RPF, 7.7 +/- 2.4 vs. 16.5 +/- 0.7 ml/min g kidney wt in controls, experimental values given are those determined 10 minutes after termination of 100 micrograms/ml RVV admixture), glomerular filtration rate (GFR 141 +/- 23 vs. 626 +/- 72 microliters/min g kidney wt) and absolute reabsorption of sodium (TNa 8 +/- 1.7 vs. 79 +/- 9 mumol/min g kidney wt), and an increased fractional excretion of sodium (FENa 60 +/- 7 vs. 8 +/- 0.8%) and water (FEH2O 68 +/- 3.2 vs. 13 +/- 1.2%). Urinary flow rate (UFR) showed both oliguric and polyuric phases. Functional alterations of this type are consistent with ARF. Light and electron microscopy of perfusion fixed IPRK revealed an extensive destruction of the glomerular filter and lysis of vascular walls. Various degrees of epithelial injury occurred in all tubular segments. In cell culture studies RVV induced a complete disintegration of confluent mesangial cell layers, beginning at concentrations of 200 micrograms/ml. In epithelial LLC-PK1 and MDCK cell cultures only extremely high doses of RVV (> 600 and 800 micrograms/ml, respectively) led to microscopically discernible damage. These results clearly demonstrate a direct dose dependent toxic effect of RVV on the IPRK, directed primarily against glomerular and vascular structures, and on cultured mesangial cells.

The effect of sodium fluoride at prophylactic and toxic doses on renal structure and function in the isolated perfused rat kidney.

To assess the renal effects of fluoride, isolated rat kidneys were perfused in single pass mode for 120 min. Five, 15 and 50, as well as 150, 500 and 1500 mumol NaF were administered 60, 80 and 100 min after starting the perfusion, respectively. Kidneys were perfused with constant pressure (100 mmHg). The perfusate consisted of a substrate supplemented Ringer solution containing hydroxy ethyl starch (HES) to produce isoncotic conditions. Concentrations below 500 mumol/l NaF did not induce major changes in the main parameters of renal function. Only upon admixture of the highest concentration of 1500 mumol/l NaF severe changes in renal function could be observed, resulting in complete anuria and a drastic reduction of renal perfusion to 5% of control, associated with a cessation of glomerular filtration. Due to the lack in tubular load, tubular reabsorptive processes inevitably declined to zero. The morphological analysis of kidneys exhibited to 500 mumol/l NaF revealed the occurrence of vesicular material within the urinary space. These vesicles could electron microscopically be identified as membrane enclosed material of podocytic origin. The interstitium was widened. Upon admixture of 1500 mumol/l NaF, kidneys responded with a decrease of the interstitial space. Moreover, epithelial cell swelling, hydropic degeneration of all proximal and distal tubular segments, bleb formation and intraluminal casts were observed frequently. Glomerular capillaries were filled with fine precipitates and their endothelium was severely damaged. The results of our studies in the isolated perfused rat kidney (IPRK) model clearly demonstrate a direct dose dependent acute nephrotoxic effect of NaF only for extremely high doses, which, however, may be reached in human cases of severe fluoride intoxication. On the contrary, for low fluoride doses, especially for those concentrations occurring in human plasma upon cariesprophylactic intake of fluorides, no signs of direct acute nephrotoxic action could be observed in the IPRK model.

Hyperosmolality regulates endothelin release by Madin-Darby canine kidney cells.

ET release by the renal epithelial Madin-Darby canine kidney (MDCK) cell line was investigated under isosmotic (300 mosmol/kg H2O; pH 7.4) and hyperosmotic (400, 500, or 600 mosmol/kg H2O) culture and assay conditions by the use of a specific and sensitive RIA. During isosmotic incubation, MDCK cells, which may be of collecting duct origin, secreted by far more ET into the cell culture supernatant (495.7 +/- 25.5 fmol.mg of protein-1.24 h-1) than did the proximal tubule-derived LLC-PK1 (2.42 +/- 0.20 fmol.mg of protein-1.24 h-1) and opossum kidney (3.12 +/- 0.47 fmol.mg of protein-1.24 h-1) cells. ET secretion by MDCK monolayers increased progressively within 24 h and then only slightly declined up to 48 h. Phosphoramidon (100 mumol/L) inhibited the constitutive ET synthesis in MDCK cells by 60%, indicating the participation of a phosphoramidon-sensitive ET-converting enzyme in the processing of bigET to ET in these cells. MDCK epithelia grown on filter inserts showed a clear polarity in their ET release. The baseline secretion of ET was 2.5 times higher to the basolateral than to the apical side, which might be in support of a predominantly basolateral action of the peptide. Short-term incubation of MDCK cells in hyperosmotic NaCl media for 24 h dose dependently decreased ET production. When urea was used as the solute to generate hyperosmolality, ET release by MDCK cells significantly increased. In contrast, when raffinose was added to increase osmolality to 500 mosmol/kg H2O, a decrease of ET production in a range similar to the effect of NaCl was seen.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelin-3 modulates glomerular filtration rate in the isolated perfused rat kidney.

The present study has been performed to evaluate hemodynamic and tubular effects of various endothelin-3 (ET-3) concentrations on the isolated perfused rat kidney. Using this experimental system we observed a profound reduction of renal perfusate flow at all ET-3 concentrations tested (50, 250 and 500 pmol/l), suggesting that the vasoconstrictive potency of ET-3 in the kidney is comparable to that described for endothelin-1 (ET-1). The effects on glomerular filtration rate (GFR) differed depending on the ET-3 dose applied. While 250 pmol/l ET-3 increased GFR by 30%, 500 pmol/l ET-3 markedly reduced GFR. 50 pmol/l ET-3 did not alter GFR although renal vascular resistance significantly increased. Infusion of 1 mumol/l N-nitro-L-arginine, a specific and potent inhibitor of nitric oxide synthesis in endothelial cells, abolished the GFR elevation induced by 250 pmol/l ET-3. In parallel with the changes of GFR we observed an increase in sodium reabsorption at 250 pmol/l and a decrease of this parameter at 500 pmol/l ET-3. Moreover, an ET-3 concentration (500 pmol/l), which induced a dramatic fall in tubular sodium load, led to an increase of fractional sodium excretion and to a decrease of renal oxygen consumption. We conclude that ET-3 is a potent vasoconstrictor in the isolated perfused rat kidney. Furthermore, it modulates GFR in a differentiated mode, depending on the concentration used. The GFR increase at 250 pmol/l ET-3 seems to be mediated by endothelium-derived nitric oxide. In addition to its glomerular action, ET-3 might also affect tubular sodium transport.

Tissue distribution of neutrophils in postischemic acute renal failure.

Polymorphonuclear neutrophil granulocytes (PMNs) seem to participate in the pathogenesis of renal ischemic reperfusion injury. The kidneys from male Sprague Dawley rats were immersion-fixed after 45 min of renal artery clamping followed by reperfusion for 0, 5, 20, and 120 min, respectively. The tissue distribution of PMNs in the kidneys was studied histochemically using naphthol AS-D chloroacetate esterase as a specific marker for these cells. Neutrophil counts per unit sectional area were obtained for renal cortex, outer and inner medulla. In the cortex separate intraglomerular and peritubular counts, and in the outer medulla separate outer and inner stripe counts were made. After 120 min of reperfusion the total renal PMN counts were 488 +/- 62 (n = 4) compared with 54 +/- 4 (n = 4) per cm2 in nonischemic controls. Within 120 min of reperfusion PMN counts increased by a factor of 8 in the cortex, of 12 in the outer medulla and of 14 in the inner medulla, compared with controls. The ratio of intraglomerular against peritubular PMN counts was approximately 2 in controls, but 0.5 after a 120-min reperfusion interval. The outer stripe of the outer medulla contained only a small number of PMNs whereas PMN counts of 923 +/- 197 (n = 4) per cm2 were found in the inner stripe after 120 min reperfusion. Interestingly, there was a marked increase in PMNs in the inner stripe during the first 5 min of reperfusion but no extravasation of PMNs was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Morphology of renal tubular damage from nephrotoxins.

The proximal renal tubular cells' vulnerability to the direct toxic action of chemicals is largely due to the role played by this nephron portion in absorption and secretion. This is an energy-demanding function so that these cells must have a high rate of oxidative metabolism and thus contain many mitochondria supplying the Na+/K+ pumps at the basolateral plasma membrane domain, thereby driving the carrier systems for entry of water and solutes across the luminal membrane. Thus toxic mechanisms leading directly or indirectly to disturbances of the renal cells' energy metabolism will result in cell injury and acute renal insufficiency. Quantitative morphological-stereological-analysis of at least two, the mercuric chloride- and the maleate-induced experimental models of toxic acute renal failure, show a very early substantial loss of ATP-generating mitochondrial inner membrane surface as well as substantial decrease in those functions protecting cells against oxidative or auto-oxidative processes, i.e. glutathione content, activities of the free-radical-scavenging systems superoxide dismutase, glutathione peroxidase and glutathione reductase and catalase. The cellular dysfunction following these early events may be considered as causative of the subsequent development of most of the morphological alterations described, which are fairly similar in appearance regardless of the toxic principle acting upon the kidney.