Ischemia-induced Acute Renal Failure Research Articles

Reduced abundance of aquaporins in rats with bilateral ischemia-induced acute renal failure: prevention by alpha-MSH.

We examined the effect of temporary renal ischemia (30 min or 60 min) and reperfusion (1 day or 5 days) on the expression of renal aquaporins (AQPs) and urinary concentration in rats with bilateral ischemia-induced acute renal failure (ARF). Next, we tested whether reducing ischemia/reperfusion (I/R) injury by treatment with alpha-melanocyte stimulating hormone (alpha-MSH) affects the expression of AQPs and urine output. Rats with ARF showed significant renal insufficiency, and urinary concentration was markedly impaired. In rats with mild ischemic injury (30 min), urine output increased significantly to a maximum at 48 h, and then nearly normalized within 5 days. Consistent with this, semiquantitative immunoblotting revealed that kidney AQP1 and AQP2 abundance was significantly decreased after 24 h to 30 +/- 5% and 40 +/- 11% (n = 8) of controls (n = 9), respectively (P < 0.05). Five days after ischemia, AQP2 abundance was not significantly decreased and urine output was normalized. In contrast, severe ischemic injury (60 min) resulted in a marked reduction in urine output at 24 h, despite a significant decrease in urine osmolality and solute-free water reabsorption, T(c)H(2)O. AQP1 and AQP2 abundance was markedly decreased to 51 +/- 5% and 31 +/- 9% (n = 10) of controls (n = 8) at 24 h (P < 0.05). After 5 days, the rats developed gradually severe polyuria and had very low AQP2 and AQP1 levels [11 +/- 4% and 6 +/- 2% (n = 5) of controls (n = 8), respectively; P < 0.05]. A similar reduction was observed for AQP3. The reduction in AQP expression in the proximal tubule and inner medullary collecting duct was confirmed by immunocytochemistry. Next, we found that intravenous alpha-MSH treatment of rats with ARF significantly reduced the ischemia-induced downregulation of renal AQPs and reduced the polyuria. In conclusion, the I/R injury is associated with markedly reduced expression of the collecting duct and proximal tubule AQPs, in association with an impairment of urinary concentration. Moreover, alpha-MSH treatment significantly prevented the reduction in expression of AQPs and renal functional defects. Thus decreased AQP expression is likely to contribute to the impairment in urinary concentration in the postischemic period.

Expression of bone morphogenetic protein-7 mRNA in normal and ischemic adult rat kidney.

BMP-7, a member of the bone morphogenic protein subfamily (BMPs) of the transforming growth factor-beta superfamily of secreted growth factors, is abundantly expressed in the fetal kidney. The precise role of this protein in renal physiology or pathology is unknown. A cDNA that encodes rat BMP-7 was cloned and used as a probe to localize BMP-7 mRNA expression by in situ hybridization in the adult rat kidney. The highest expression of BMP-7 mRNA could be seen in tubules of the outer medulla. In glomeruli, a few cells, mainly located at the periphery of the glomerular tuft, showed specific and strong signals. Also, high BMP-7 mRNA expression could be localized to the adventitia of renal arteries, as well as to the epithelial cell layer of the renal pelvis and the ureter. Preliminary evidence suggests that BMP-7 enhances recovery when infused into rats with ischemia-induced acute renal failure. We examined BMP-7 mRNA expression in kidneys with acute renal failure induced by unilateral renal artery clamping. BMP-7 mRNA abundance as analyzed by solution hybridization was reduced in ischemic kidneys after 6 and 16 h of reperfusion compared with the contralateral kidney. In situ hybridization in ischemic kidneys showed a marked decrease of BMP-7 mRNA in the outer medulla and in glomeruli. Utilizing rat metanephric mesenchymal cells in culture, we also demonstrate that BMP-7 induces epithelial cell differentiation. Taken together, these data suggest that BMP-7 is important in both stimulating and maintaining a healthy differentiated epithelial cell phenotype.

Endothelin up-regulation and localization following renal ischemia and reperfusion

Endothelin (ET), a potent vasoconstrictor, is known to play a role in ischemic acute renal failure. Although preproET-1 (ppET-1) mRNA is known to be up-regulated following ischemia/reperfusion injury, it has not been determined which component of the injury (ischemia or reperfusion) leads to initial gene up-regulation. Likewise, although ET-1 peptide expression has been localized in the normal kidney, its expression pattern in the ischemic kidney has not been determined. Therefore, the purpose of this study was twofold: (a) to determine whether ischemia alone or ischemia plus reperfusion is required for the up-regulation of ppET-1 mRNA to occur, and (b) to localize ET-1 peptide expression following ischemia in the rat kidney to clarify better the role of ET in the pathophysiology of ischemia-induced acute renal failure. Male Lewis rats underwent clamping of the right renal vascular pedicle for either 30 minutes of ischemia (group 1), 60 minutes of ischemia (group 2), 30 minutes of ischemia followed by 30 minutes of reperfusion (group 3), or 60 minutes of ischemia followed by three hours of reperfusion (group 4). The contralateral kidney acted as a control. ppET-1 mRNA up-regulation and ET-1 peptide expression were examined using the reverse transcription-polymerase chain reaction and immunohistochemistry, respectively. Reverse transcription-polymerase chain reaction yielded a control (nonischemic) value of 0.6 +/- 0.2 densitometric units (DU) of ppET-1 mRNA in the kidney. Group 1 levels (30 min of ischemia alone) were 1.8 +/- 0.4 DU, a threefold increase (P < 0.05). Group 2 levels (60 min of ischemia alone) increased almost six times above baseline, 3.5 +/- 0.2 DU (P < 0.01), whereas both group 3 and group 4 (ischemia plus reperfusion) did not experience any further significant increases in mRNA levels (1.9 +/- 0.4 DU and 2.8 +/- 0.6 DU, respectively) beyond levels in group 1 or 2 animals subjected to similar ischemic periods. ET-1 peptide expression in the ischemic kidneys was significantly increased over controls and was clearly localized to the endothelium of the peritubular capillary network of the kidney. Initial ET-1 gene up-regulation in the kidney occurs secondary to ischemia, but reperfusion most likely contributes to sustaining this up-regulation. The marked increase of ET-1 in the peritubular capillary network suggests that ET-induced vasoconstriction may have a pathophysiological role in ischemic acute tubular necrosis.

Novel Sodium Binding Properties of Some Cyclopentapeptide Endothelin A Selective Receptor Antagonists: Electrospray and Fast-Atom-Bombardment Mass Spectrometric Studies

Electrospray ionization and fast atom bombardment mass spectrometric methods reveal novel interactions of endothelin A selective receptor antagonists, cyclo(D-Trp-D-Asp-Pro-D-Val-Leu), cyclo(D-Trp-D-Glu-Ala-D-allo-Ile-Leu) and cyclo(D-Trp-D-Asp-Pro-D-Ile-Leu) with sodium ions. The peptides have very high intrinsic affinities for sodium ions, and form multiple sodium adducts and sandwich structures: [M + Na]+, [M + 2Na − H]+, [M + 3Na − 2H]+, [M + 4Na − 3H]+, [M + 5Na − 4H]+, [2M + Na]+, [2M + 2Na − H]+, [2M + 3Na − 2H]+, [2M + 4Na − 3H]+, [2M + 5Na − 4H]+, [2M + 6Na − 5H]+, and [2M + 7Na − 6H]+. The three cyclic peptides exhibit similar sodium binding stoichiometries despite differences in their amino acids. The observed sodium binding properties may have implications in understanding their protective effects against ischemia-induced acute renal failure. Those cyclic peptides that offer protection may be those that have high affinities for multiple sodium ions.

Down regulation of kidney neutral endopeptidase mRNA, protein and activity during acute renal failure: possible mechanism for ischemia-induced acute renal failure in rats?

Neutral endopeptidase (NEP, 24.11) is an ectoenzyme involved in the degradation of peptide hormones such as endothelin (ET), atrial natriuretic factor and enkephalins. The current study was designed to assess the involvement of NEP in ischemia-induced acute renal failure (ARF). In unilaterally nephrectomized Sprague-Dawley rats, the left renal artery was occluded for 30 min under pentobarbital anesthesia (40 mg/kg, i.p.) at 37 degree C. In addition to plasma creatinine levels, NEP activity was determined in renal cortical membranes at 0, 2, 5, and 24 h following reperfusion. Plasma creatinine levels significantly increased at 2, 5 and 24 h. There was a significant decrease in NEP activity as early as 2 h following reperfusion that was maintained up to 24 h (57.9 +/- 4%) with a concomitant loss of enzyme protein shown by Western analysis. Northern analysis of kidney cortical RNA, probed with an NEP cDNA, showed a 45% decrease in NEP mRNA level by the end of the ischemic period and decreased further during reperfusion. Thus, decrease in NEP mRNA levels preceded the changes in protein level, enzyme activity and plasma creatinine levels. These data, along with the reported increase in the tissue level of ET in kidney cortex, and the beneficial effect of ET antibody as well as ET receptor antagonist in ARF, suggest that down regulation of NEP, one of the mechanisms leading to increased tissue level of ET, may be a contributing factor to ARF.

Macrophage and myofibroblast involvement in ischemic acute renal failure is attenuated by endothelin receptor antagonists

Endothelin (ET) may be a mediator of injury following ischemia-induced acute renal failure (ARF). ET receptor (ETR) antagonists have been reported to increase survival rates and lower serum creatinines when administered postrenal ischemia-reperfusion injury in the rat. Renal cellular and extracellular matrix responses to this therapy have not been addressed. We investigated the use of ETR antagonists, PD 156707 (ETA) and SB 209670 (ETA and ETB) in the treatment of sublethal postischemic ARF. The right kidney of female Sprague-Dawley rats weighing approximately 200 g was removed. After five days, the left renal pedicle was occluded for 45 minutes. Twenty-four hours after renal ischemia, one of two ETR antagonists, PD 156707 (N = 7) or SB 209670 (N = 8), was administered. Experimental animals were compared with an ischemic group receiving only saline (N = 9). Three nephrectomized groups that did not undergo ischemia but that received infusions of saline (N = 6), PD 156707 (N = 6), and SB 209670 (N = 6), respectively, were also studied. Animals were sacrificed one week postischemia. Quantitation of monocytes and macrophages (Mo/Mphi), alpha-smooth muscle actin-positive myofibroblasts, and collagens type III and IV was performed by immunohistochemical staining. Cell kinetics were examined by staining for apoptosis with terminal deoxyuridine triphosphate (dUTP) nick end labeling and for proliferation with proliferating cell nuclear antigen. All ischemic groups of rats initially developed raised serum creatinine levels; however, no significant difference was observed between the groups (Kruskal-Wallis). Creatinines returned to preischemic values in all groups by the time of sacrifice. No significant difference in kidney weights or body weights was found between groups. Histologically, infiltration of Mo/Mphi was significantly reduced in groups treated with ETR antagonists (P < 0.001). The presence of myofibroblasts was also significantly reduced in the antagonist-treated groups (P < 0. 001). This was also paralleled by reduced quantities of collagen IV in the treated rat groups (P < 0.001). The interstitial area was also significantly greater in the saline group (P < 0.001). The amount of collagen III did not significantly differ between rat groups. Apoptosis was reduced (P < 0.001) by treatment with ETR antagonists, whereas proliferation was enhanced (P < 0.005). All non-ischemic groups showed no variation in any parameter studied at this time point. Treatment of ischemic ARF in the rat with ETR antagonists PD 156707 and SB 209670 attenuated cellular infiltration and matrix accumulation. An advantage of one antagonist over the other could not be determined in this study. The marked discrepancy between function and pathology (former unchanged, latter markedly improved) may be due to the time frame of this experiment, and longer outcome measures need to be assessed.

Effect of YM435, a Dopamine DA 1 Receptor Agonist, in a Canine Model of Ischemic Acute Renal Failure

1. The effects of (-)-( S)-4-(3,4-dihydroxyphenyl)-1,2,3,4-tetrahydroisoquinoline-7,8-diol monohydrochloride monohydrate (YM435), a dopamine DA1 receptor agonist, were evaluated in a canine model of ischemic acute renal failure (ARF). 2. ARF was induced by clamping the left renal artery for 1 hr and subsequent reperfusion of the left kidney in anesthetized uninephrectomized dogs. 3. After 1-hr complete renal artery occlusion, an intravenous infusion of either YM435 (0.3 μg/kg/min) or 0.9% saline (vehicle) was begun and continued for 1 hr. 4. In the vehicle group, renal ischemia markedly decreased glomerular filtration rate, urine flow and urinary sodium excretion. The YM435 group was characterized by significant recoveries in glomerular filtration rate, urine flow, and urinary sodium excretion as compared with the vehicle group. 5. These results indicate that YM435 can facilitate recovery in glomerular filtration rate, urine flow, and urinary sodium excretion in a canine model of ARF induced by ischemia. YM435 may be useful in the preservation of renal function in ischemia-induced ARF.

Upregulation of Osteopontin in Ischemia-Induced Renal Failure in Rats: A Role for ET-1?

In this study, the involvement of osteopontin in a rat model of ischemia-induced acute renal failure (ARF) was evaluated. In unilaterally nephrectomized Sprague Dawley rats where the left artery was occluded for 30 min., plasma creatinine levels increased significantly within two hours following reperfusion indicating the onset of renal failure. Northern analysis of kidney cortical RNA from these rats showed a time-dependent increase in osteopontin mRNA expression that was significantly higher than sham-operated rats. Since endothelin-1 (ET-1) is implicated as a mediator of acute renal failure, we evaluated its effects on osteopontin expression in a rat mesangial cell-line. Data fromin vitrostudies indicated that endothelin-1 (ET-1) caused a modest but reproducible increase in osteopontin mRNA in these cells. While the signal for osteopontin upregulation in the rat model is not known, ET-1, which is known to be increased during ischemia, may contribute at least in part to this process.

Reversal of postischemic acute renal failure with a selective endothelinA receptor antagonist in the rat.

Studies were designed to examine the effect of a selective endothelinA (ETA) receptor antagonist, BQ123, on severe postischemic acute renal failure (ARF) in Sprague-Dawley rats. Severe ARF was induced in uninephectomized, chronically instrumented rats by 45-min renal artery occlusion. BQ123 (0.1 mg/kg.min) or vehicle was infused intravenously for 3 h on the day after ischemia. Measurements before infusion (24 h control) showed a 98% decrease in glomerular filtration rate (GFR), increase in fractional excretion of sodium from 0.6 to 39%, and in plasma K+ from 4.3 to 6.5 mEq/liter. All vehicle-treated rats died in 4 d because of continuous deterioration of renal function, resulting in an increase of plasma K+ to fatal levels (> 8 mEq/liter). Infusion of BQ123 significantly improved survival rate (75%) by markedly improving tubular reabsorption of Na+ and moderately increasing GFR and K+ excretion. Plasma K+ returned to basal levels by the 5th d after ischemia. Improved tubular function was followed by gradual recovery in GFR and urinary concentrating mechanism. Additional data from renal clearance studies in rats with moderate ARF (30-min ischemia) and in normal rats with intact kidneys showed that ETA receptor blockade increases Na+ reabsorption and has no effect on renal hemodynamics. These results indicate that in the rat, the ETA receptor subtype mediates tubular epithelial function, and it plays a significant role in the pathogenesis of ischemia-induced ARF. Treatment with the selective ETA receptor antagonist reverses deteriorating tubular function in established ARF, an effect of possible therapeutic significance.

Epidermal growth factor in acute renal failure.

Epidermal growth factor (EGF) is produced in large amounts in the kidney in the form of a membrane-bound high molecular weight precursor. This precursor is inserted in the apical plasma membrane of the EGF-producing cells, which are localized in the thick ascending limb and distal convoluted tubule in mouse and rat kidney, and probably also in human kidney. High levels of EGF are excreted in urine, although renal tissue contains little mature EGF. It modulates renal cell proliferation and differentiation in vitro, but the role of the distal tubular EGF and/or its precursor in vivo is unknown. The expression of EGF in the kidney and its liberation into the urine are quickly abolished during several types of drug- or ischemia-induced acute renal failure and also in ureteral obstruction. Moreover, its expression is restored only after morphological and functional recovery of the kidney. This absence of EGF in conditions in which its mitogenic properties would be most appropriate suggests that the EGF of renal origin is not acting as a mitogen during kidney regeneration. Nevertheless, since the number of EGF receptors, which are localized at the basolateral cell surface in most nephron segments, is increased in regenerating renal epithelia, EGF of systemic origin or other members of the EGF family of growth factors, released from infiltrated inflammatory cells at the sites of injury, could enhance cellular proliferation by interacting with the EGF receptor. Administration of EGF indeed has a mildly beneficial effect on recovery from acute renal injury.

Endogenous EGF as a potential renotrophic factor in ischemia-induced acute renal failure

The time course for the increases in soluble renal epidermal growth factor (EGF) after ischemia has been established. These elevated levels of EGF have been compared with the degree of tissue injury as well as the extent of cell proliferation in the recovering tissue. Levels of soluble immunoreactive EGF (irEGF) in control animals were 9.74 +/- 1.1 ng/g wet wt (n = 4-8 for all values) and rose to 83.9 +/- 30 ng/g within 12 h after injury. Soluble irEGF content peaked at 88.8 +/- 15 ng/g at 24 h postinjury and returned to control values by 72 h. We previously reported that trypsin digestion of crude renal membranes (CRM) generates rat EGF that is indistinguishable from that isolated from the submandibular gland. Initial levels of trypsin-releasable membrane-associated irEGF were 439 +/- 26 ng/g. These levels fell to 46.6 +/- 9.6 ng/g at 48 h after injury. The total renal EGF demonstrated an 80% decline 48 h after injury but returned to 50% of the initial values after 72 h representing significant new synthesis of EGF-containing proteins between 48 and 72 h postinjury. Immunohistochemical staining of kidney paraffin sections for EGF immunoreactivity demonstrated staining intensities that paralleled the amount of irEGF in the trypsin-digested CRM fraction, suggesting that the membrane-associated irEGF is the predominant form detected by this technique. Regenerative hyperplasia subsequent to tubular insult was monitored by immunostaining nuclei of S phase cells after pulse labeling with the thymidine analogue 5-bromo-2'-deoxyuridine. Cell proliferation was particularly prominent in the outer stripe of outer medulla of kidneys exposed to ischemia and reached a maximum (19-fold higher than the baseline value) 48 h after reperfusion. Renal cell turnover returned to control values by day 7. The observation that the peak in soluble EGF levels (24 h) precedes the peak in tubular regeneration (48 h) by 24 h is consistent with the hypothesis that EGF is one of the mitogenic signals triggering regenerative hyperplasia after renal injury.

Sodium azide protects against ischemia-induced acute renal failure in rats.

Sodium azide (AZ) is a nitrovasodilator with diverse biochemical properties. We found that low doses of AZ led to a profound protective effect against postischemic, acute renal failure (ARF) in rats. AZ, given at 250 micrograms/kg iv, before 25 min of renal artery occlusion (RAO) and again before reperfusion, conferred almost complete protection against loss of kidney function determined 18 h after RAO. The effect of AZ was evidenced by a higher creatinine clearance (+348%) and lower levels of blood urea nitrogen (-69%) and histological renal damage (-50%) compared with ischemic control animals. Indexes of kidney function in AZ-treated animals subjected to RAO were not significantly different from those of nonischemic control animals. Two other nitrovasodilators, sodium nitroprusside and hydralazine, at doses which produced decreases in blood pressure similar to that of AZ, were ineffective at preventing ARF. The beneficial effect of AZ may be due to its known ability to inhibit one or more enzymes including adenosinetriphosphatase, cytochrome-c oxidase, and myeloperoxidase.

Increased soluble EGF after ischemia is accompanied by a decrease in membrane-associated precursors

We have characterized the distribution of immunoreactive epidermal growth factor (irEGF) in control and ischemia-injured rat kidneys. Kidneys that had undergone ischemic injury contained levels of soluble irEGF that were six times those of uninjured kidneys. The predominant forms of soluble irEGF were native and des-Arg-epidermal growth factor (EGF), both of which are biologically active. Crude membrane fractions from whole kidneys were solubilized in Triton X-100 and tested for irEGF. Amounts of irEGF were slightly decreased in the ischemia-injured kidney membranes. However, when solubilized membrane fractions were digested with trypsin, which generates a single immunoreactive species which appears identical to native EGF, the amount of irEGF in control fractions increased 13-fold and the amount in injured fractions increased only 4-fold as measured by radioimmunoassay. To better characterize the membrane-associated irEGF, Triton X-100-solubilized membrane fractions from control animals were affinity purified and subjected to high-performance liquid molecular sieve chromatography. Three major peaks of material exhibited immunoreactivity to EGF antibodies, bound the EGF receptor, and stimulated [3H]thymidine incorporation in growth-arrested fibroblasts. Trypsin digestion of the two high-molecular-mass peaks enhanced these activities. The third peak eluted with native EGF and showed no change in activity with trypsin addition. We propose that EGF is released from membrane-associated EGF precursors and can then act in an autocrine or paracrine fashion to promote cell growth after ischemia-induced acute renal failure.

Reduced renal prepro-epidermal growth factor mRNA and decreased EGF excretion in ARF

Levels of prepro epidermal growth factor (EGF) mRNA in renal cortical tissue and urinary EGF excretion have been determined during cisplatin and ischemia-induced acute renal failure in the rat. Northern analysis of polyadenylated RNAs of kidney cortical tissue showed diminished renal preproEGF mRNA in rats injected with cisplatin (5 mg/kg). The decrease in preproEGF mRNA occurred as early as 12 hours in the kidney and persisted for at least three days after cisplatin injection. The submandibular gland, a major site of EGF synthesis, contained normal levels of preproEGF mRNA. Transplatin, a non-nephrotoxic isomer of cisplatin, did not reduce renal preproEGF mRNA levels. Northern analysis of polyadenylated RNAs of kidney cortical tissue 24 hours after a 50 minute period of renal pedicle clamping also showed reduced preproEGF mRNA levels. By contrast, cisplatin increased renal c-fos mRNA. Urinary EGF excretion was also reduced after cisplatin and ischemia and the decrease in EGF excretion correlated significantly with the degree of renal failure. The data show that nephrotoxic and ischemic renal cell injury reduces preproEGF mRNA and urinary EGF excretion. Reduced preproEGF mRNA and diminished EGF excretion may be important in the functional and regenerative responses to renal injury.

The effect of α-human atrial natriuretic peptide on the incidence of acute renal failure in cadaveric kidney transplantation

In previous studies in humans, mannitol (20%, 250 ml) has been shown to reduce the incidence of acute renal failure (ARF) after transplantation from 54% to 19%. In rats, atrial natriuretic peptide appears to prevent ischemia-induced ARF. We therefore decided to evaluate the effects of alpha-human atrial natriuretic peptide (alpha-h-ANP) both alone and combined with mannitol during transplantation in humans. First, we demonstrated that systemic alpha-h-ANP infusion during kidney transplantation was safe in dosages up to 0.08 micrograms/kg per minute. In these patients the calculated metabolic clearance rate of alpha-h-ANP was relatively low ranging from 0.68 to 1.80 l/min. In a second study of 11 renal graft recipients, no mannitol was used and alpha-h-ANP (0.05 micrograms/kg per minute) was infused into the donor kidney artery during transplantation for 46 +/- 2 min, followed by IV administration for 71 +/- 2 min. Our aim was to reduce the incidence of ARF. Nevertheless, ARF occurred immediately after surgery in four of the patients (36%) in this group and, as a result, mannitol was reintroduced. A third group of nine renal graft recipients received alpha-h-ANP (total dose 400 micrograms) as five IV injections within 90 min after transplantation. ARF occurred in four of these patients (44%). We conclude that alpha-h-ANP, administered according to the aforementioned protocols in such small groups of patients, does not seem to be of value in the prevention of ARF after transplantation.

The effect of α-human atrial natriuretic peptide on the incidence of acute renal failure in cadaveric kidney transplantation

Abstract. In previous studies in humans, mannito (20%, 250 ml) has been shown to reduce the in cidence of acute renal failure (ARF) after transplan tation from 54% to 19%. In rats, atrial natriuretic peptide appears to prevent ischemia-induced ARF We therefore decided to evaluate the effects of α-human atrial natriuretic peptide (α-h-ANP) both alone and combined with mannitol during transplantation in humans. First, we demonstrated thai systemic α-h-ANP infusion during kidney transplantation was safe in dosages up to 0. 08 μg/kg pei minute. In these patients the calculated metabolic clearance rate of α-h-ANP was relatively low ranging from 0. 68 to 1. 801/min. In a second study of 11 renal graft recipients, no mannitol was used and α-h-ANP (0. 05 μg/kg per minute) was infused into the donor kidney artery during transplantation for 46 ± 2min, followed by IV administration for 71 ± 2 min. Our aim was to reduce the incidence of ARF. Nevertheless, ARF occurred immediately after surgery in four of the patients (36%) in this group and, as a result, mannitol was reintroduced. A third group of nine renal graft recipients received α-h-ANP (total dose 400 μg) as five IV injections within 90 min after transplantation. ARF occurred in four of these patients (44%). We conclude that α-h-ANP, administered according to the aforementioned protocols in such small groups of patients, does not seem to be of value in the prevention of ARF after transplantation.

The angiotensin converting enzyme inhibitor enalapril in acute ischemic renal failure in rats.

The influence of the renin-angiotensin system on renal hemodynamics, tubular pressure and tubulo-glomerular feedback was investigated with the angiotensin converting enzyme inhibitor MK 421 (enalapril), in uninephrectomized rats with and without ischemia-induced acute renal failure. In animals with normal renal function proximal tubular pressure and tubulo-glomerular feedback response were lowered by enalapril long-term treatment, whereas glomerular filtration rate and renal blood flow were not influenced by the drug. After 45 and 70 minutes ischemia there was no difference between treated and untreated animals in the severely impaired glomerular filtration rate. Renal blood flow remained unaffected by the treatment. The histological damage due to ischemia (tubular casts, tubular necrosis and medullary capillary congestion) was not influenced by enalapril. As tubulo-glomerular feedback had been significantly inhibited during renin-angiotensin inhibition, its importance in mediating acute renal failure remains doubtful; other factors such as tubular obstruction and medullary congestion may be crucial.

Theophylline in rats during maintenance phase of post-ischemic acute renal failure

We have shown previously that theophylline increases both renal plasma flow (RPF) and glomerular filtration rate (GFR) during the initiation phase of post-ischemic acute renal failure (ARF) in rats. The purpose of the present experiments was to determine the effects of theophylline during the maintenance phase of ARF, five days after initiation. Clearance techniques were used to measure renal function in a control group of pentobarbital anesthetized rats (group C) and in three experimental groups, five days after subjecting the left kidney to a thirty-minute period of complete ischemia. Group SS received saline during both the ischemic episode and the clearance measurements; group ST received saline during ischemia and theophylline, acutely, during the clearance measurements; group TS received theophylline during ischemia and saline during the clearance measurements. In comparison with the values for the control group (group C), RPF and GFR of the post-ischemic left kidneys of group SS were approximately half normal. In groups ST and TS, RPF and GFR of the left kidneys were higher than in group SS. Collectively, these results demonstrate that pretreatment with theophylline during the initiation phase of ischemia-induced ARF leads to increased RPF and GFR during the maintenance phase, and that acute theophylline treatment during the maintenance phase acutely increases RPF and GFR. Since increases in GFR were associated with increases in RPF, and since theophylline is an adenosine receptor antagonist, these results are consistent with the hypothesis that adenosine-mediated hemodynamic changes play a pathogenic role in ischemia-induced ARF in rats.

Pathogenesis of acute renal failure following temporary renal ischemia in the rat.

In this study, we characterized the sequence of several intrarenal events and evaluated their relative importance in the pathogenesis of unilateral oliguric acute renal failure induced experimentally in rats by complete occlusion of a renal artery for 1 hour. Kidneys were studied prior to occlusion and 1-3 hours and 22-26 hours after release of the temporary occlusion. Renal blood flow measured by an electromagnetic flow transducer was reduced to 40-50% of control during both postocclusion periods. Flow of tubular fluid was markedly reduced, and the damaged kidneys were oliguric. Proximal and distal convolutions were filled with fluid and dilated 1-3 hours after occlusion; their pressures were greatly heterogeneous and were elevated, on the average, to 31 and 16 mm Hg, respectively. Glomerular capillary pressure at this time was normal or slightly increased. Histological sections showed extensive tubular obstruction. We conclude that initially the oliguria is primarily due to intraluminal obstruction in the absence of predominant increases in preglomerular vascular resistance. Observations at 22-26 hours after occlusion indicated acute tubular necrosis. Moreover, the combined involvement of preglomerular vasoconstriction, presisting tubular obstruction, and passive backflow of tubular fluid appeared to be important in the maintenance of the oliguria. Glomerular capillary, proximal intratubular, and peritubular capillary hydrostatic pressures were reduced below control values. After acute volume expansion, the reduced pressures and renal blood flow were reversed, yet the experimental kidneys remained oliguric. Thus, it is clear that tubular obstruction is a significant factor responsible for both the genesis and the maintenance of oliguria in this experimental model of ischemia-induced acute renal failure.