Proximal tubular injury attenuates outer medullary hypoxic damage: studies in perfused rat kidneys

The straight segment (S3) of the proximal tubule is predominantly damaged during renal ischemia-reflow, whereas medullary thick ascending limbs (mTALs) are principally affected in other models of hypoxic acute tubular necrosis (ATN). Since the latter injury pattern largely depends on the extent of reabsorptive activity during hypoxic stress, we hypothesized that proximal tubular damage might attenuate downstream mTAL injury by means of diminished distal solute delivery for reabsorption. In isolated rat kidneys perfused for 90 min with oxygenated Krebs-Henseleit solution, mTAL necrosis developed in 75 +/- 3% of tubules in the mid-inner stripe of the outer medulla. By contrast, S3 segments in the outer stripe were minimally affected, with tubular fragmentation involving some 5 +/- 2% of tubules. In kidneys subjected in vivo to proximal tubular injury and subsequently used for isolated perfusion studies, the injury pattern was inverted: following 20 and 30 min ischemia and reflow for 24 h, S3 fragmentation rose to 18 +/- 16% and 72 +/- 13%, while mTAL damage was reduced to 33 +/- 10 and 24 +/- 8%, respectively. In kidneys subjected in vivo to D-serine S3 necrosis rose to 100%, while mTAL damage fell to 1 +/- 1% (p < 0.001). Substantial S3 tubular collapse (involving approximately 30% of tubules) and inner stripe interstitial hemorrhage were also noted, exclusively in kidneys subjected to ischemia-reflow. Proximal tubular necrosis alone or in combination with collapse inversely correlated with mTAL necrosis (R = -0.51 and -0.72, respectively, p < 0.003). This cogent inverse association might imply that disruption of the proximal nephron attenuates downstream mTAL necrosis by a reduction of distal tubular reabsorptive workload.     

Determinants of intrarenal oxygenation: factors in acute renal failure.

Oxygen tension within the renal parenchyma is influenced by two factors: metabolic demand and oxygen supply. There are three regions within the kidney in which there is an anatomical basis for limited oxygen availability. The first is the inner stripe where oxygen diffusion between arterial and venous vasa recta reduces PO2. The other two are the outer stripe and medullary rays which are fed by O2-poor blood from venous vasa recta. The balance between oxygen demand and supply is most critical in the inner stripe where the PO2 is most influenced by transport activity. In contrast, altering transport activities in the outer stripe will not change the prevalence of hypoxic S3 injury but will alter its type (i.e., cell fragmentation related to high GFR and increased workload versus cell edema related to low GFR and minimal workload). The effect of transport activity on medullary ray PO2 has not been well defined. Using sensitive oxygen microelectrodes, cortical PO2 (52 +/- 2 mm Hg) in the rat was found to be higher than medullary PO2 (21 +/- 2 mm Hg, p less than 0.001). How are these observations reflected in current models of acute renal failure? The ischemia-reflow model affects proximal tubules with a predilection for S3 (located within the outer stripe of medulla) after short-term ischemia. With hyperfiltration (induced by glycine or renal hypertrophy) and the pursuant increase in transport related O2 demand, hypoxic mTAL inner stripe injury becomes prominent. Renal parenchymal hypertrophy exaggerates injury in the contrast nephropathy model, in which mTAL inner stripe injury is a predominant feature and medullary PO2 is very low.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hypothyroidism protects against free radical damage in ischemic acute renal failure

The effect of hypothyroidism on ischemic acute renal failure was studied in rats. Ten days after thyroidectomy with parathyroid reimplantation, rats underwent right uninephrectomy followed by occlusion of the left renal artery for 60 min. Plasma creatinine was lower in thyroidectomized than control rats 24 hr after ischemia; 1.3 +/- 0.5 vs. 3.2 +/- 0.6 mg%; P less than 0.05. Twenty-four hours after ischemia, inulin clearance was higher in thyroidectomized than control animals (0.40 +/- 0.06 vs. 0.17 +/- 0.03 mliter/min; P less than 0.01), despite an initially lower inulin clearance in thyroidectomized animals (0.81 vs. 1.1 +/- 0.07 mliter/min; P less than 0.05). Administration of the antithyroid drug prophylthiouracil for 14 days also resulted in lower plasma creatinine after ischemia. Kidneys from thyroidectomized animals showed less histologic damage 24 hr after ischemia. Renal cortical content of the lipid peroxidation product malondialdehyde was increased less in thyroidectomy than control kidneys after 60 min ischemia plus 15 min reflow (0.08 +/- 0.02 vs. 0.42 +/- 0.1 nmole/mg protein; P less than 0.005). Renal cortical glutathione content was higher in thyroidectomized animals by approximately 36%, 650 +/- 46 vs. 479 +/- 32 nmole/mg protein (P less than 0.02). In normal rats, glutathione infusion also increased renal cortical glutathione content and resulted in lower plasma creatinine 24 hr after renal artery ischemia. Therefore, hypothyroidism resulted in functional and histologic protection against injury after ischemia. Post-ischemic renal lipid peroxidation was reduced in thyroidectomized animals, perhaps the result of increased scavenging of reactive oxygen species (oxygen free radicals and H2O2) by glutathione.     

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.     

Compensated heart failure predisposes to outer medullary tubular injury: studies in rats

BACKGROUND: Heart failure (HF) is considered a putative factor predisposing to acute renal failure (ARF). Since outer medullary hypoxic injury may play an important role in the pathogenesis of acute tubular necrosis, we explored the impact of experimental HF on the propensity to develop ARF with hypoxic medullary injury following the inhibition of prostaglandin and nitric oxide synthesis. METHODS: Compensated, high-output HF was induced in Sprague-Dawley rats by aorto-caval fistula. At the eighth to ninth postoperative day, the rats were injected with indomethacin and N(omega) nitro-L-arginine methyl ester (L-NAME; ARF protocol) and were sacrificed 24 hours later for morphologic evaluation. RESULTS: Kidney function comparably declined in HF-ARF rats and in control sham operated animals (CTR-ARF). Nevertheless, outer medullary hypoxic damage with medullary thick ascending limb (mTAL) necrosis occurred almost exclusively in the HF-ARF group (11 +/- 4% vs. 0.2 +/- 0.2% of tubules in CTR-ARF, P < 0.03). In a third group of HF animals subjected to vehicles only (HF-Nil), kidney function was preserved and renal morphology remained intact. Papillary-tip necrosis was consistently found in all animals subjected to indomethacin and L-NAME, irrespective of preconditioning. Morphometric evaluation disclosed that HF was not associated with mTAL hypertrophy. CONCLUSIONS: Incipient HF predisposes to hypoxic outer medullary injury, probably reflecting the impact of regional vasoconstrictive stimuli rather than tubular hypertrophy when protective local vasodilating mechanisms are hampered. The presence and extent of outer medullary hypoxic damage cannot be predicted from the functional derangement, which in the experimental settings may also represent prerenal azotemia or papillary damage.     

Renal medullary Na-K-ATPase and hypoxic injury in perfused rat kidneys

We wished to see if chronic alterations in Na-K-ATPase activity in the medullary thick ascending limb would modify the susceptibility of its cells to the hypoxic injury produced by perfusion of the isolated kidney. Rats were fed a diet high (64%) or low (8%) in protein for three weeks. Renal medullary Na-K-ATPase was 75 +/- 12 U/mg protein/hr (mean +/- SE) in the high protein group and 44 +/- 3 in rats given low protein. After 90 minutes of perfusion, the kidneys of rats fed a high protein diet showed almost all mTAL cells near the inner medulla with severe damage (93 +/- 4.8%), whereas the same zone in perfused kidneys of rats on a low protein diet showed only 47 +/- 7.7% injury. In a similar fashion, damage to mTAL cells seen in perfused kidneys was greatly augmented by compensatory renal hypertrophy produced by removal of the contralateral kidney two weeks earlier, and by a diet high in potassium given for two weeks, procedures which also increased the activity of medullary Na-K-ATPase. The results suggest that the level of transport work of medullary cells mediated by Na-K-ATPase is a determinant of the vulnerability of mTAL cells to hypoxic injury.     

Selective ADH-induced hypertrophy of the medullary thick ascending limb in Brattleboro rats

A morphometric study was undertaken to quantitate the morphologic changes induced by ADH availability in the rat kidney. Homozygous Brattleboro rats with hereditary diabetes insipidus (DI) (no ADH) were compared to heterozygous Brattleboro control rats (HZ) and to DI rats after 5 to 6 weeks of continuous ADH infusion by implantable Alzet osmotic minipumps (TDI). ADH resulted in a 37% increase in mass of kidney per unit body wt. All kidney zones and all nephron segments were not increased uniformly. The inner stripe was enlarged more than other renal zones. It represented 15.5 +/- 0.7% of the total kidney height along the cortico-papillary axis in DI and 22.2 +/- 1.5% in TDI (P less than 0.025). The volume of the inner stripe in DI and TDI amounted to 10.9 +/- 0.9 and 18.0 +/- 1.0% of the total kidney volume, respectively (P less than 0.001). Selective increases in tubular diameter and cell height, due mostly to an hypertrophy of pre-existing cells, were observed in the earliest part of the thick ascending limbs (TAL) in the inner stripe, resulting in a twofold increase in epithelial volume per unit tubular length (P less than 0.001). Volume density of mitochondria and surface density of basolateral membranes were unchanged but, due to the increase in cell volume and inner stripe thickness, the amount of mitochondria and the surface area of basolateral membrane in the TAL were more than tripled in the inner stripe of treated rats. These changes provide a much greater salt transport capacity in the TAL of treated rats. They probably represent an adaptation of the early TAL to an enhanced sodium chloride transport in response to a direct ADH stimulation and/or to an increased salt delivery to this segment in the concentrating kidney.     

Effect of glycine on medullary thick ascending limb injury in perfused kidneys

The addition of 2 mM glycine to the recirculating perfusate of isolated perfused rat kidneys almost completely prevented the severe morphological injury to tubular cells lining the medullary thick ascending limb (mTAL) that normally develops in this preparation. Glycine was similarly effective in reducing mTAL injury associated with hypoxic perfusion, indomethacin and amphotericin. Fractional reabsorption of sodium was increased with glycine, without any change in perfusate flow to the whole kidney and without consistent improvement in GFR. L-alanine demonstrated a similar though less pronounced cytoprotective action, but glutamine, cysteine, glutamate, cysteine plus glutamate, 1-serine and 4-aminoisobutyric acid all had little or no effect in preventing severe mTAL injury. The protective effect of glycine was unimpaired by the arginine analogue NG-monomethyl-l-arginine (L-NMMA), suggesting that the endothelial-derived relaxing factor, NO, was not involved. The action of glycine was not reduced by the addition of a substrate (benzoate) or a product (hippurate) of the glycine N-acyltransferase reaction. Glycine did not depress the respiration of dispersed mTALs prepared from rat kidneys. The cytoprotective effect of glycine in the mTAL of perfused kidneys, shared with l-alanine, appears to be relatively specific for these amino acids and probably unrelated to a diminution in cell work.     

Protective effect of prostacyclin on postischemic acute renal failure in the rat

Infusion of prostacyclin (PGI2) reportedly attenuates renal ischemic injury in the dog and the rat. In the dog, PGI2 is a potent renal vasodilator; in the rat a direct action on the renal vasculature is not always apparent. To determine whether or not the protective effect of PGI2 on postischemic ARF was hemodynamically mediated, studies were performed in uninephrectomized Sprague-Dawley rats before and after a 40 minute period of complete renal artery occlusion. In response to the preischemic infusion of PGI2 for 30 minutes at 160 ng/kg body wt/min i.v. (N = 7), MAP and RBF fell to 86 +/- 7% (P less than 0.0001) and 84 +/- 9% (P less than 0.05) of baseline values, respectively. RVR initially declined to 81 +/- 9% of baseline values (P less than 0.025) but returned to 102 +/- 13% of baseline values prior to the period of ischemia. Following the period of ischemia, reflow of blood in the rats receiving PGI2 was delayed when compared to rats not receiving PGI2 (N = 7). RBF returned to only 76 +/- 19% of the initial values in PGI2-treated rats (P less than 0.01) but to 90 +/- 12% of the initial values in rats receiving buffer alone (NS).(ABSTRACT TRUNCATED AT 250 WORDS)     

Mannitol stimulates atrial natriuretic peptide release in humans

The purpose of this study was to determine if mannitol stimulates atrial natriuretic peptide (ANP) release in humans and to examine potential mechanisms for this effect. Twenty patients requiring cardiac catheterization were randomized to receive either mannitol (15-g bolus followed by 15% infusion mixed in 75 mmol/L saline at 100 mL/h for 1 hour) or an equal volume of 75 mmol/L saline, intravenously (IV). All measurements were made at three time points: at baseline, at 10 minutes (after the bolus but before radiocontrast administration), and at 60 minutes (after completion of the study). Baseline plasma ANP (PANP) measurements (mean +/- SE) were similar in both groups (saline, 73 +/- 38 pg/mL; mannitol, 62 +/- 11 pg/mL). PANP increased significantly over time for the set of all patients (analysis of variance [ANOVA], P less than 0.05); however, at 10 minutes PANP increased significantly only in the group receiving mannitol (saline, 76 +/- 43 pg/mL; mannitol, 100 +/- 29 pg/mL) (P less than 0.04). Serum osmolality (SOSM), over time for the set of all patients (ANOVA, P less than 0.04). At 10 minutes there were significant increases only in the group receiving mannitol, and after radiocontrast, there were significant increases in both groups for all parameters. Regression analysis demonstrated a significant correlation between the change in PANP and the change in SOSM (P less than 0.04, r = 0.33). In conclusion, intravascular infusion of mannitol or radiocontrast increased PANP levels. The mechanism may be multifactorial, with a potential role for an increase in SOSM and/or PADH.     

Early renal medullary hypoxic injury from radiocontrast and indomethacin.

We evaluated the acute changes in cortical and outer medullary oxygen tension and the alterations in renal function and morphology within the first 90 minutes after the administration of indomethacin and iothalamate to anesthetized Sprague-Dawley rats. Both agents were found to produce marked and protracted outer medullary hypoxia averaging 12 +/- 4 and 9 +/- 2 mm Hg, respectively (mean +/- SE). Given together to salt depleted uninephrectomized rats they produced an early hypoxic injury localized selectively in the outer medulla. This lesion progressed from 3 +/- 1% of medullary thick ascending limbs (mTALs) at 15 minutes to 22 +/- 7% at 24 hours. Condensed "dark" cells were observed at 15 minutes, probably representing a type of early injury. Residual red cell mass, quantified in the outer medullary vasculature of perfusion-fixed kidneys and presumably reflecting stasis, was substantially increased in iothalamate treated rats. Red cell mass in the interbundle zone correlated with mTAL necrosis. Taken together, these results show an early period of medullary hypoxia, accompanied by a selective injury to mTALs in the central interbundle zone with apparent stasis. These findings contrast sharply with the ischemia-reflow pattern of renal damage and emphasize the important role of medullary hypoxia in the genesis of acute renal failure in this model.     

Effects of graded oxygen tension on adenosine release by renal medullary and thick ascending limb suspensions.

Adenosine is released from renal cells, and extracellular adenosine may influence the effects of ischemia on medullary tubule segments by altering ion transport or renal hemodynamics. While adenosine release and excretion are enhanced during renal ischemia, the specific sites of renal adenosine production have not been completely elucidated. In the present study, extracellular adenosine concentrations in suspensions of renal outer medulla and thick ascending limb segments were quantitated by reversed-phase high performance liquid chromatography. Media from other medullary (OM) suspensions incubated for 8 and 15 minutes at 0% oxygen contained significantly greater amounts of adenosine (1.404 +/- 0.21 and 2.034 +/- 0.27 ng/micrograms protein, respectively), when compared to values obtained from media of suspensions incubated for equivalent periods under non-hypoxic conditions (8, 20, and 95% oxygen), 0.78 +/- 0.05 (8 min) and 1.37 +/- 0.21 ng/micrograms protein (15 min). Similarly, adenosine release was greater in medullary thick ascending limb (mTAL) suspensions incubated for 8 minutes at 0% versus 8% oxygen (0.81 +/- 0.17 vs. 0.20 +/- 0.12 ng/micrograms protein, respectively). Moreover, the observed increase in adenosine release by thick ascending limbs at 0% oxygen could be inhibited completely by either furosemide or ouabain. These studies demonstrate that: 1) the renal medulla and medullary thick ascending limb are sites of adenosine release; 2) adenosine release by the mTAL is enhanced significantly during hypoxic conditions; and 3) the increased release of adenosine during hypoxia appears to be related to ion transport and oxidative metabolism, as the increased release was prevented by two disparate inhibitors of transport in this segment.     

Role of the urinary concentrating process in the renal effects of high protein intake

High protein diet is known to increase glomerular filtration rate (GFR) and induce kidney hypertrophy. The mechanisms underlying these changes are not understood. Since the mammalian kidney comprises different nephron segments located in well-delineated zones, it is conceivable that the hypertrophy does not affect all kidney zones and all nephron segments uniformly. The present experiments were designed to study the chronic effects of high or low isocaloric protein diets (HP = 32% or LP = 10% casein, respectively) on kidney function and morphology in Sprague-Dawley rats. HP diet induced significant increases in kidney mass, GFR, free water clearance, and maximum urine concentrating ability. Kidney hypertrophy was characterized by: 1. a preferential increase in thickness of the inner stripe of the outer medulla (IS) (+54%, P less than 0.001, while total kidney height, from cortex to papillary tip, increased only by 18%); 2. a marked hypertrophy of the thick ascending limbs (TAL) in the inner stripe (+40% epithelium volume/unit tubular length, P less than 0.05) but not in the outer stripe nor in the cortex; 3. an increase in heterogeneity of glomeruli between superficial (S) and deep (D) nephrons (D/S = 1.47 in HP vs. 1.17 in LP, P less than 0.05). In contrast, normal kidney growth with age and kidney hypertrophy induced by uninephrectomy were not accompanied by preferential enlargement of IS structures. The morphologic changes induced by high protein intake parallel those we previously reported in rats fed a normal diet (25% protein) but in which the operation of the urine concentrating mechanism was chronically stimulated by ADH infusion or by reduction in water intake.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of iron in postischemic renal injury in the rat

To determine whether iron participates in free radical-mediated postischemic renal injury and lipid peroxidation, we examined the effects of removal of endogenous iron or provision of exogenous iron following renal ischemia, as well as the effects of renal ischemia and reperfusion on renal venous and urinary "free" iron. Rats underwent 60 minutes of renal ischemia and were studied after either 24 hours (inulin clearance) or 15 minutes (renal malondialdehyde content) of reperfusion. Infusion of the iron chelator deferoxamine (200 mg/kg/hr) during the first 60 minutes of reperfusion resulted in a marked improvement in renal function (inulin clearance: 879 +/- 154 vs. 314 +/- 74 microliter/min; P less than 0.025) and a reduction in lipid peroxidation (renal malondialdehyde: 0.449 +/- 0.06 vs. 0.698 +/- 0.08 mmol/mg prot; P less than 0.05) compared to control animals. Infusion of 50 mg/kg/hr deferoxamine also protected renal function after ischemia (inulin clearance: 624 +/- 116 vs. 285 +/- 90 microliter/min; P less than 0.05) and resulted in less histologic injury. Iron-saturated deferoxamine had no protective effect. Conversely, infusion of the iron complex EDTA-FeCl3 during reperfusion exacerbated postischemic renal dysfunction and lipid peroxidation. Following renal ischemia there was no detectable increase in "free" iron in arterial or renal venous plasma. However, urinary "free" iron increased 10- to 20-fold following reperfusion. Iron chelators which underwent filtration and gained access to this free iron in the urine (free deferoxamine or inulin-conjugated deferoxamine) provided protection, whereas a chelator confined to the vascular space (dextran-conjugated deferoxamine) did not.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glucagon potentiates intestinal reperfusion injury

Vasoactive agents, including glucagon, have been used in treatment of mesenteric ischemia. Such drugs change both intestinal blood flow and metabolism. Since reperfusion injury reflects the metabolic state of an organ as well as the duration and severity of ischemia, we investigated the effect of glucagon in a standard model of intestinal ischemia. Data were generated from denervated isoperfused rat small intestinal preparations (n = 39). Arterial and venous pressures, intestinal blood flow, and oxygen consumption were monitored. Animals were subjected to 15, 30, or 45 minutes of ischemia followed by 1 hour reperfusion. Experiments were performed without drug infusion or during intravenous glucagon administration (0.1, 0.2, or 0.4 micrograms/kg/min). After the rats were killed, histologic sections of intestine were graded 1 through 5 in a blinded fashion with 1 = normal villi and 5 = severe injury. Results (mean +/- SD) were analyzed by analysis of variance (*p less than 0.05). Glucagon at all concentrations increased intestinal blood flow and oxygen consumption before ischemia. For example, with 0.2 micrograms/kg/min glucagon, intestinal blood flow increased from 80.78 +/- 13.5 to 114.79 +/- 21.02 ml/min.100 gm* and oxygen consumption increased from 3.65 +/- 0.73 to 5.73 +/- 1.37 ml/min.100 gm.* Mucosal injury after ischemia reflected duration of ischemia and glucagon infusion rate. At all ischemic intervals, increased glucagon concentrations were associated with greater mucosal injury. In fact the histologic injury with 15 minutes of ischemia + 0.2 microgram/kg/min glucagon (3.04 +/- 0.49) exceeded that of 30 minutes of ischemia (2.87 +/- 0.06).(ABSTRACT TRUNCATED AT 250 WORDS)     

Renal effects of N-acetylcysteine in patients at risk for contrast nephropathy: decrease in oxidant stress-mediated renal tubular injury.

BACKGROUND: N-Acetylcysteine has been shown to protect against contrast nephropathy, although the mechanisms underlying such an effect are unclear. Surprisingly, studies have shown that post-radiocontrast renal function actually improves in chronic renal failure patients receiving N-acetylcysteine. However, there have been no studies investigating the cause of this improvement. METHODS: In a double-blind, placebo-controlled study, 24 patients (aged 65+/-2 years) suffering from stable mild-to-moderate renal insufficiency and undergoing elective coronary angiography were randomized to receive either placebo or N-acetylcysteine. All received similar hydration. Renal function parameters were assessed 48 h before and 48 h after radiocontrast administration. Urinary 15-isoprostane F2(t), a specific marker of oxidative stress, was measured immediately before and after the procedure. Expression of urinary alpha-glutathione S-transferase protein, a specific proximal tubular injury marker, was assessed after the procedure. RESULTS: Comparing creatinine clearance values before and after angiography, a significant increase was seen in N-acetylcysteine patients (44.7+/-4.2 vs 57.2+/-6.3 ml/min/1.73 m(2); P = 0.02), whereas placebo patients presented no change (46.6+/-5.0 vs 46.9+/-4.3 ml/min/1.73 m(2); P = 0.90). After radiocontrast, urinary 15-isoprostane F2(t) levels in placebo patients increased significantly over baseline values (2.9+/-0.7 vs 10.3+/-2.1 ng/mg creatinine; P = 0.007), whereas urinary 15-isoprostane F2(t) levels in N-acetylcysteine patients remained basically unchanged (3.5+/-0.5 vs 4.1+/-0.9 ng/mg creatinine; P = 0.63). Furthermore, N-acetylcysteine treatment led to lower levels of alpha-glutathione S-transferase than did placebo treatment (0.8+/-0.2 vs 2.4+/-0.7 micro g/g; P = 0.046). CONCLUSIONS: In chronic renal failure patients, the improvement in renal function induced by post-radiocontrast administration of N-acetylcysteine is strongly associated with suppression of oxidant stress-mediated proximal tubular injury.     

Histamine: a promoter of xanthine oxidase activity in intestinal ischemia/reperfusion.

Xanthine oxidase (XO)-derived oxygen radicals are thought to play an important role in the intestinal injury resulting from ischemia and reperfusion. In vitro data shows enhanced XO activity in the presence of histamine. Histamine is known to be released during intestinal ischemia and reperfusion. The purpose of this study was to evaluate the relationship between histamine and XO in vivo in intestinal ischemia/reperfusion injury. Using an established model of gut ischemia and reperfusion, portal venous plasma was obtained and assayed for histamine levels, XO activity, and xanthine dehydrogenase (XD) activity following injury. Intestinal ischemia for 120 minutes resulted in a 200% increase in plasma histamine levels (263.4 +/- 36.9 nmol/mL control, v 548.7 +/- 35.1 nmol/mL experimental, P less than .05). Reperfusion for 15 minutes resulted in a further increase in plasma histamine (to 658.3 +/- 33.9 nmol/mL), compared with 120 minutes of ischemia alone. No significant change in plasma XO activity resulted after simple ischemia for 120 minutes. However, XO activity doubled within 15 minutes of reperfusion of the ischemic intestine (6.37 +/- 0.53 nmol O2- per milliliter per minute v 3.12 +/- 0.25 nmol O2- per milliliter per minute, P less than .05). Reperfusion for 60 minutes resulted in the maximal observed increase in plasma XO activity (9.49 +/- 0.67 nmol O2- per milliliter per minute). Analysis of XD activity demonstrated no significant decrease compared with controls until 120 minutes of ischemia and 60 minutes of reperfusion (1.62 +/- 0.49 nmol uric acid per milliliter per minute at 60 minutes of reperfusion, versus 5.02 +/- 0.52 nmol uric acid per milliliter per minute control, P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)     

GLP-2alpha accelerates recovery of mucosal absorptive function after intestinal ischemia/reperfusion

BACKGROUND/PURPOSE: The authors' previous laboratory results have shown that rats treated for 3 days with intravenous GLP-2alpha, a synthetic protease-resistant form of glucagonlike peptide-2, showed increased mucosal mass and absorptive function when compared with saline-treated controls after intestinal ischemia/reperfusion (I/R). This study was designed to explore the temporal relationship between injury that occurs secondary to intestinal I/R and recovery of mucosal absorptive function with and without GLP-2alpha treatment. METHODS: Each of 18 male Sprague-Dawley rats (300 to 333 g) was subjected to superior mesenteric artery occlusion for 30 minutes, during which time a jugular venous catheter was placed and connected to a subcutaneous infusion pump. Rats were divided into 4 groups based on the type and duration of infusion as follows: group 1, systemic saline at 1 microL/h for 24 hours (n = 5); group 2, systemic GLP-2alpha at 100 microg/kg/d for 24 hours (n = 5); group 3, systemic saline at 1 microL/h for 72 hours (n = 4); and group 4, systemic GLP-2alpha at 100 microg/kg/d for 72 hours (n = 4). Immediately after the infusions, (14)C-galactose and (14)C-glycine absorption was measured using an in vivo, closed-recirculation technique and expressed as micromoles per square centimeter intestine +/- SEM. Statistical analysis was performed using analysis of variance. RESULTS: Twenty-four hours after intestinal I/R injury, there was a decrease in substrate absorption but no significant difference between the saline and GLP-2alpha-treated groups (galactose absorption, 1.13 +/- 0.09 in group 1 v 1.35 +/- 0.11 in group 2, P =.15; glycine absorption, 1.18 +/- 0.13 in group 1 v 1.34 +/- 0.15 in group 2, P =.36). However, after the 72-hour infusion, absorption of galactose and glycine was significantly increased in the rats receiving GLP-2alpha as compared with the saline-infused control group (galactose absorption, 1.24 +/- 0.13 in group 3 v 1.88 +/- 0.10 in group 4, P <.01; glycine absorption, 1.64 +/- 0.07 in group 3 v 2.05 +/- 0.08 in group 4, P <.05). Compared with previously determined levels of absorption in normal, uninjured rat intestine (1.50 +/- 0.12 micromol/cm(2) for galactose and 1.85 +/- 0.17 micromol/cm(2) for glycine), after I/R a 72-hour infusion of GLP-2alpha increased galactose absorption 26% (P <.05) and glycine absorption 11% (P =.29) beyond baseline. CONCLUSIONS: When initiated at the time of intestinal I/R, a continuous infusion of GLP-2alpha accelerated recovery of mucosal absorptive function in rats. Remarkably, carbohydrate absorption at 72 hours was increased to a level significantly greater than that in normal, uninjured rat intestine. J Pediatr Surg 36:570-572.     

Protective role of furosemide and saline in radiocontrast-induced acute renal failure in the rat

Acute renal failure (ARF) can be produced in rats by a combination of insults which augment transport activity and blunt regulatory mechanisms designed to maintain medullary oxygen sufficiency. This type of ARF is characterized by necrosis of medullary thick ascending limbs (mTALs). Uninephrectomized, salt-depleted rats injected with indomethacin (10 mg/kg) develop ARF following the administration of the radiocontrast agent, iothalamate. Furosemide (20 mg/kg, intravenous), administered immediately before the contrast material, attenuated the severity of ARF and reduced mTAL necrosis. Treatment with furosemide and/or normal saline prevented both the decline in renal function and mTAL injury. It is concluded that furosemide and normal saline may ameliorate the course of ARF if administered before radiocontrast.