Kurt L. Berens

PENTOXIFYLLINE IN THE ISOLATED PERFUSED RAT KIDNEY

The effects of pentoxifylline, a new methylxanthine with marked hemorrheologic properties, were studied following brief renal artery occlusion in the isolated rat kidney model perfused with cell-free Krebs-Henseleit buffer. Anuria was observed in 3 of 6 control kidneys within 5 min after reperfusion; urine flow was maintained in all rat kidneys perfused with pentoxifylline (2500 ng/ml). Glomerular filtration rate was significantly greater in kidneys administered pentoxifylline compared with controls following 40 min of postocclusion reperfusion (460 +/- 100 vs. 100 +/- 110 microliters/min/gKW; P less than 0.01). Pretreatment of kidneys with indomethacin, a nonspecific cyclooxygenase inhibitor, blocked the protective effects of pentoxifylline in this setting. These data suggest that the addition of pentoxifylline may prevent hypoxia-related changes in renal function of transplanted kidneys. Stimulation of renal prostaglandin synthesis, as well as an interaction at the level of the adenosine receptors, were most likely responsible for the observed beneficial effects of pentoxifylline.

Role of Vascular Decongestion in Ischemic Acute Renal Failure Defined by Postinsult Administration of Pentoxifylline

The patholophysiologic significance of vascular congestion in the mechanism of ischemic acute renal failure following postocclusive reflow was studied with a novel hemorheologic probe, pentoxifylline. Using the autoperfused rat kidney model, inulin clearances (CIN), urine flow rates (UFR), renal electrolyte excretions, and renal hemodynamic parameters (RVR, RBP, RBF) were compared in saline- and pentoxifylline-treated anesthetized rats prior to and following a 45-min occlusive period. Renal functional and hemodynamic parameters were significantly altered in saline controls. In contrast, postischemia treatment with pentoxifylline was associated with significant recovery in CIN and UFR, and stable RVR, RBF, and RBP. Kidneys treated with saline infusion had pronounced vascular congestion, in contrast to those administered pentoxifylline. Coupled with the absence in medullary hyperemia, the present experiments support the role of vascular congestion in ischemic acute renal failure. Pentoxifylline, administered in pharmacologic doses after the insult, provided benefit during the initiation phase of postischemic acute renal failure. These data strengthen the opinion that ischemic insult results in vascular congestion, and that restoration of blood flow will prevent further deterioration in renal function.

Role of Neutrophils and Macrophages in Experimental Nephrosis of the Rat

The single dose administration of the aminonucleoside of puromycin (PAN) induces a nephrotic syndrome in rats characterized by massive proteinuria and progressive histologic changes. This model of acute parenchymal nephritis is thought to be mediated by the renal recruitment of monocytes and macrophages. To investigate the role of leukocytes in the experimental nephrotic syndrome model, the effects of two methylxanthines, pentoxifylline (45 mg/kg i.p. twice daily) and torbafylline (5 mg/kg i.p. twice daily) were compared with controls over a 2-week period. Pentoxifylline treatment was associated with 3- and 6-fold reductions in urinary protein excretion at 7 and 14 days, respectively, compared with PAN-treated control animals (p < .01). Similarly, 14-day dosing of torbafylline resulted in a 3-fold decrease in urinary protein excretion. Glomerular filtration and electrolyte excretion rates were similar between all treatment groups. There were significant reductions in glomerular neutrophil and macro-phage counts, but not T-cells (OX19+) or suppressor/cytotoxic T-cells (0X8+), in kidneys of rats given either treatment compared with PAN con-trol rats. In summary, both pentoxifylline and torbafylline attenuated the proteinuria and glomerular macrophage and neutrophil infiltration associated with PAN administration. These data support the role of macrophages and neutrophils in the pathogenesis of acute parenchymal injury and the potential role of pentoxifylline or related analogues in the attenuation of the ensuing renal deficit associated with minimal lesion disease.

Benefit of Vascular Decongestion in Glycerol-Induced Acute Renal Failure

The post insult administration of vascular decongestants has resulted in attenuation of experimental acute renal failure (ARF) following the introduction of various nephrotoxins including drugs, heavy metals, and endotoxin. In the present study, the dose-dependent effects of a novel methylxanthine, HWA-138, were studied in the glycerol-induced murine model of ARF. Renal function, assessed by serial inulin clearances at 24 and 48 h after glycerol injection, urinary electrolyte excretion rates, and renal morphology, was compared between controls and those given glycerol and single i.v. doses of 0.1, 0.5, 1.0, 5.0, and 10.0 mg/kg of HWA-138, or physiologic saline. Whereas significant renal dysfunction was found in all animal groups given glycerol, the mean inulin clearance values of animals given HWA-138 1 mg/kg closely approximated values found in control rats. There were no changes in renal electrolyte excretion rates in animals given HWA-138 compared with relative natriuresis found in untreated glycerol ARF rat. Although a modest decrease in medullary congestion was associated with rats given 1 mg/kg of HWA-138, there was no obvious structural improvement found with HWA-138. The present data provide further evidence of the potential of methylxanthines in the glycerol-ARF murine model.

Attenuation of amphotericin-B nephrotoxicity in the candidiasis rat model

Dose-limiting nephrotoxicity has hampered the clinical usefulness of amphotericin-B (AmpB). Recently, vascular decongestants, such as pentoxifylline, have shown benefit in reducing drug-associated renal damage of AmpB in rats. The present study investigated a dose-dependent protection of a structurally similar methylxanthine, HWA-448, in the candidiasis rat model given a single dose of AmpB. Forty-eight hours after inoculation with Candida albicans, each rat was treated with 0.8 mg/kg of AmpB or sterile water; animals were further randomized to receive 0.5, 1, 5, or 10 mg/kg i.v. of HWA-448 or saline given every 12 h for 3 doses. Kidney fungal counts, morphology, and renal function were compared between treatment groups upon completion of the study. Rats administered AmpB with HWA-448 had markedly improved renal function compared with those given AmpB alone; these effects were independent of the administered dose of HWA-448. The antifungal effect of AmpB was not impaired with concomitant HWA-448. Marked accumulation of granulomas and organisms was found in all rat groups. In summary, coadministration of low doses of HWA-448 attenuated the dose-limiting nephrotoxicity without impairing the antifungal effect of AmpB.

Circadian assessment of lipids in the hyperphagic obese rat compared with lean litter-mates

Time and feeding influences on cholesterol, triglyceride, glucose and insulin levels, and serum cholinesterase activity were assessed in a genetically-hyperlipidemic hyperphagic obese rat model, and compared with its lean litter-mate. Following a 28-day acclimation to a 12-hr light/dark cycle, blood samples were obtained every 2 hr from rats via tail bleed for a 24-hr period. Synchronization with other animal studies was established by endogenous serum cortisol levels [acrophase 18-20 hr after light onset (HALO) in both groups]. Triglycerides cholesterol, insulin and glucose levels were significantly elevated in obese versus lean rats. Obese rats were observed to feed throughout the 24-hr cycle, whereas lean litter-mates ate only during the dark cycle. No circadian rhythmicity was found in glucose levels with either rat group. Insulin levels were not correlated. Although triglyceride levels peaks at 13 HALO in lean rats, no pattern was observed in obese rats. Cholesterol levels were unchanged with time in either group. Cholinesterase activity followed a circadian rhythm in the lean, but not obese, rats with an acrophase estimated at 8 HALO. In contrast to previous reports, enzyme activity was not correlated with triglyceride levels in either rat group. Circadian similarities in insulin levels between rat groups suggest changes in insulin metabolism and/or secretion which are likely to be independent of feeding or activity. Conversely, triglyceride levels remained elevated throughout the 24-hr period in obese rats, whereas significant increases were observed in lean rats during the dark active cycle. These data suggest that triglyceride levels, and not insulin and cholesterol levels, are most likely dependent on feeding patterns.

Effects of suprofen on the isolated perfused rat kidney.

Although suprofen has been associated with the development of acute renal failure in greater than 100 subjects, the mechanism of damage remains unclear. The direct nephrotoxic effects of a single dose of 15 mg of suprofen were compared in the recirculating isolated rat kidney perfused with cell-free buffer with or without the addition of 5 mg/dL of uric acid. There were no significant differences in renal sodium excretion, oxygen consumption, or urinary flow rates in kidneys perfused with suprofen compared with the drug-free control groups. In contrast, a significant decline in glomerular filtration rate was found after the introduction of suprofen to the kidney perfused with uric acid; no changes were found with suprofen in the absence of uric acid. A significant decrease in the baseline excretion rate of uric acid was found in rats given suprofen, compared with drug-free controls. However, the fractional excretion of uric acid was unchanged between the groups over the experimental period. In summary, suprofen causes acute declines in renal function, most likely by directly altering the intrarenal distribution of uric acid.