Joseph I. Shapiro

Ischemic preconditioning attenuates functional, metabolic, and morphologic injury from ischemic acute renal failure in the rat.

Ischemic preconditioning has been shown to ameliorate injury due to subsequent ischemia in several organs. However, relatively little is known about preconditioning and the kidney. To address this, rats were randomized to control (C, N = 14), 2 min of ischemic preconditioning (P2 N = 10), 3 periods of 2 min of ischemia separated by 5 min periods of reflow (P2,3 N = 7), or three 5 min periods of ischemia separated by 5 min of reflow (P5,3 N = 6) prior to 45 min of bilateral renal ischemia followed by 24 hours of reperfusion. We observed a lower serum creatinine after 24 hours of reflow in P2, P2, 3 but not P5, 3 rats compared with C. Histology was examined in the C and P2, 3 groups and demonstrated less severe injury in the P2, 3 group. To gain insight into the mechanism by which preconditioning ameliorated ischemic injury, we performed near IR spectroscopy and 31P NMR spectroscopy. Based on near IR spectroscopy, the P2, 3 group had closer coupling of cytochrome aa3 redox state with that of hemoglobin during reflow. In the 31P NMR studies, the changes in ATP and pHi were similar during ischemia, but the P2, 3 group recovered ATP and pHi faster than C. These data suggest that ischemic preconditioning may ameliorate ischemic renal injury as assessed by functional, metabolic and morphological methods. The mechanism(s) by which this occurs requires additional study.

Tubular Hypermetabolism as a Factor in the Progression of Chronic Renal Failure

Thus, in summary, we hypothesize that nephron loss by a time-limited insult (eg, an acute immunological insult, surgical removal of five sixths of normal nephrons) may cause events in the tubules of the remaining nephrons that contribute substantially, though not exclusively, to the inexorable progression to ESRD. Specifically, hypermetabolism in the remaining tubules as assessed by oxygen consumption and ATP synthesis rates has been found to occur. This hypermetabolism in residual nephrons appears to be due to the known increased sodium transport per nephron, but nonsodium transport events also appear to be involved. With respect to the latter phenomenon, we propose that an increase in growth factor response per tubule, as a mechanism of renal hypertrophy, activates the DAG----protein kinase C----Na/H antiporter system. We have evidence in support of this sequence of events by the demonstration of a two-fold increase in membrane (particulate) protein kinase C within 24 hours after removal of the contralateral kidney and an increase in intracellular pH as assessed by NMR spectroscopy. Activation of the Na/H antiporter not only leads to proton extrusion and cellular alkalinization, which may activate cellular alkalinization, which may activate cellular enzymes such as phospholipases, but also increases intracellular Na concentration, thereby further increasing Na/K-ATPase, ATP use, and enhancing ATP synthesis. The increase in mitochondrial oxygen consumption, which accompanies the enhanced ATP synthesis, would be expected to be associated with increased oxygen radicle generation. If the tissue scavengers of oxygen radicles are not sufficient to scavenge the increase in oxygen radicles, then lipid peroxidation and tissue damage will occur.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of verapamil on renal function after warm and cold ischemia in the isolated perfused rat kidney.

The potential usefulness of verapamil, a calcium channel blocker to renal allograft preservation, was investigated using the isolated perfused rat kidney. Two models of ischemic injury were used. In the first model, rat kidneys were exposed to 40 min of 37† C ischemia on the perfusion circuit. Addition of verapamil in doses of 2.5, 5, and 100 μM concentration to the perfusate significantly improved inulin clearance (Cin) and total sodium absorption (TNa) in the hour of reperfusion following ischemia. Regeneration of adenosine triphos-phate (ATP) and total adenine nucleotide TAN levels during reperfusion following warm ischemia were also significantly higher in verapamil-treated kidneys. In the second model, rat kidneys were flushed in situ with Collins C2 solution and stored at 0† C for 8 hr. After this period of cold ischemia, they were perfused on a perfusion circuit with perfusion media. Verapamil 2.5 μM was absent from both flush and perfusate (control), or added to just the flush, both the flush and perfusate, or just the perfusate. Addition of verapamil to the flush or the flush and perfusate significantly improved Cin, urine flow rate (V) and TNa during reperfusion, compared with control. Addition of verapamil to just the perfusate did not effect Cin Tna, or V but did significantly increase RPF. These findings suggest the verapamil may protect against organ damage occurring during both warm and cold ischemia in the absence of any systemic effects and thus may be useful for renal allograft preservation.

Loss of epithelial polarity: A novel hypothesis for reduced proximal tubule Na+ transport following ischemic injury

SummaryIschemia results in the marked reduction of renal proximal tubule function which is manifested by decreased Na+ and H2O reabsorption. In the present studies the possibility that altered Na+ and H2O reabsorption were due to ischemia-induced loss of surface membrane polarity was investigated. Following 15 min of renal ischemia and 2 hr of reperfusion, proximal tubule cellular ultrastructure was normal. However, abnormal redistribution of NaK-ATPase to the apical membrane domain was observed and large alterations in apical membrane lipid composition consistent with loss of surface membrane polarity were noted. These changes were associated with large decreases in Na+ (37.4vs. 23.0%,P<0.01) and H2O (48.6vs. 36.9%,P<0.01) reabsorption at a time when cellular morphology, apical Na+ permeability, Na+-coupled cotransport, intracellular pH and single nephron filtration rates were normal. We propose that the abnormal redistribution of NaK-ATPase to the apical membrane domain is in part responsible for reduced Na+ and H2O reabsorption following ischemic injury.

Increased Nephron Oxygen Consumption: Potential Role in Progression of Chronic Renal Disease

We have previously reported that remnant kidneys demonstrate marked increases in oxygen consumption (QO2) when normalized for sodium transport as compared with normal kidneys. This increase in oxygen consumption could be attenuated by dietary maneuvers such as protein restriction and phosphate restriction and also by calcium channel blockers. The basis of this enhanced metabolic activity, however, has not been fully defined. Furthermore, circumstances of increased oxygen consumption are associated with enhanced oxygen radical generation. These oxygen radicals could lead to renal tissue lipid peroxidation if the remnant kidney contains insufficient oxygen radical scavengers. This review summarizes available evidence for increased nephron oxygen consumption as a cause of tubulointerstitial injury and its relationship to progression of chronic renal disease.

Mucormycosis in Deferoxamine-Treated Patients on Dialysis

Excerpt To the editor: Deferoxamine has been increasingly used to treat iron and aluminum overload in uremic patients on dialysis. Because of the lack of renal function, the half-life of deferoxami...

P-31 nuclear magnetic resonance spectroscopic evaluation of heterotopic cardiac allograft rejection in the rat

P-31 nuclear magnetic resonance (NMR) spectroscopy was used to evaluate heterotropic cardiac allograft rejection in the rat. To enable optimal application of NMR spectroscopy for the in vivo study of myocardial metabolism in the transplanted organ, an accessory heart transplantation to groin in the rat was used. The allografts were studied in a 1.89 Tesla horizontal bore magnet. Each spectrum was obtained by Fourier transform of 512 scans using 60-degree pulses with 2-sec delays. Changes in phosphocreatine (PCr), adenosine 5-triphosphate (ATP), and inorganic phosphate (Pi) and intracellular pH as determined by P-31 NMR were compared with rejection process as judged by histological studies. Allografts treated with cyclosporine (CsA) did not show any rejection (NR) and had relatively high levels of PCr, and low levels of Pi. Allografts that did not receive any CsA revealed both vascular and cellular rejection. These rejected allografts (R) had relatively low levels of PCr and high levels of Pi. It is concluded that P-31 NMR spectroscopy may have potential application to the clinical diagnosis of cardiac allograft rejection.

Intraocular Pressures During High-Flux Hemodialysis

The intraocular pressures of 16 patients with end stage renal failure treated with high-flux dialysis were measured before and during a high-flux dialysis treatment. The patients were selected so as not to have glaucoma or history of glaucoma. Intraocular pressures did not change significantly in any patients during or following a high-flux hemodialysis treatment. These data suggest that high-flux hemodialysis does not result in increases in intraocular pressure nor does it precipitate acute glaucoma in well-dialyzed patients undergoing intermittent in-center hemodialysis.

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 rejction 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 metabloities such as adenosine triphosphite 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 chossen to be rejectors received no immunosuppression while animals chose to be nonrejectors recieved 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 probable related to vascular rejection in the allografts. 31P NMR spectroscopy may have application as a noninvasive tool in the differential diagnosis of posttransplantation renal insuffieciencey.

Reduction of remnant nephron hypermetabolism by protein restriction

To study the metabolic mechanisms involved in the protective effect of dietary protein restriction on the progression of chronic renal failure, experiments were performed in Sprague-Dawley rats subjected to five-sixths nephrectomy and pair-fed on isocaloric low (4%) protein (LP) or high (50%) protein (HP) diets. Protein restriction reduced the severity of uremia, with lower blood urea nitrogen (BUN) concentrations (8.9 +/- 1.1 v 30.0 +/- 2.9 mmol/L [25 +/- 3 v 84 +/- 8 mg/dL] both n = 12, P less than 0.01), and resulted in lower mortality at 2 weeks (0% v 33%, P less than 0.05), 4 weeks (16% v 58%, P less than 0.05), and 10 weeks (16 v 83%, P less than 0.01). Isolated perfusion of the remnant kidney at 3 weeks demonstrated reduced O2 consumption (QO2) (0.77 +/- 0.2 v 2.56 +/- 0.5 mumol/min/g, both n = 7, P less than 0.05) in the absence of significant differences in inulin clearance (239 +/- 53 v 341 +/- 39 microL/min/g, NS) and net sodium reabsorption (34 +/- 8 v 49 +/- 6 mumol/min/g, NS) in rats fed the LP diet. A lower renal QO2 in protein-restricted animals was also demonstrated in vivo (4.1 +/- 0.9 v 13.8 +/- 2.7 mumol/min/g, P less than 0.01). In vivo P-31 nuclear magnetic resonance (NMR) studies of remnant kidneys did not demonstrate any difference in the steady-state tissue concentrations of adenosine triphosphate (ATP) or inorganic phosphate between rats fed LP and HP diets. Dietary protein restriction decreases the severity of uremia and diminishes renal QO2 in the remnant kidney model.(ABSTRACT TRUNCATED AT 250 WORDS)