Schematic diagram depicting mechanisms and hypothetical actions of allopurinol and probenecid in <i>vCdt</i> nephrotoxicity.

<p>ARF induced by <i>vCdt</i> occurs through indirect and direct actions leading to lethality. Direct actions of <i>vCdt</i> generate hyperuricemia and renal oxidative stress. Uric acid has direct intracellular pro-oxidative effects. Allopurinol and probenecid restore uricemia and renal oxidative stress caused by <i>vCdt</i>. These beneficial effects must be, in part, exerted through a reduction of intracellular deposit of urate, as a consequence of the reduction of uric acid formation due to the inhibition of xanthine oxidase (allopurinol) or an inhibition of an organic anion transport exchanger that blocks the entry of uric acid into the cells (probenecid). Allopurinol, but not probenecid, protects against the lethality caused by <i>vCdt</i>. This differential protective effect of allopurinol is not related to the blocking of xanthine oxidase-associated oxidants, but it is likely related to the blocking of oxidant effects of increased production of uric acid in the intracellular environment more than the entry of uric acid into the cells.</p

Effects of treatments on renal oxidative stress.

<p>Reduced glutathione (GSH), oxidized glutathione (GSSG) and malondialdehyde (MDA) were measured in renal cortex and medulla from mice treated with vehicle (control), allopurinol (NL), probenecid (PB) and <i>Crotalus durissus terrificus</i> venom (<i>vCdt</i>) followed by NL (<i>vCdt</i>+NL) or PB (<i>vCdt</i>+PB) after 2 h. Values are means ± SEM. Number of animals in parentheses. Comparison of the same parameter among groups: ANOVA (cortex: GSH, p = 0.6489; GSSG, p<0.0004; GSSG/GSH, p<0.0001; MDA, p<0.0001; medulla: GSH, p = 0.8440; GSSG, p<0.0001; GSSG/GSH, p<0.0009; MDA, p<0.0001). Post hoc Student-Newman-Keuls (different letters over the bars indicate statistical differences: p<0.05).</p

Effects of treatments on renal function parameters in the urine.

<p>Mice treated with vehicle (control), allopurinol (NL), probenecid (PB) and <i>Crotalus durissus terrificus</i> venom (<i>vCdt</i>) followed by NL (<i>vCdt</i>+NL) or PB (<i>vCdt</i>+PB) after 2 h. Values are means ± SEM of pooled animals, 16 (control), 9 (NL), 10 (PB), 12 (<i>vCdt</i>), 22 (<i>vCdt</i>+NL) and 12 (<i>vCdt</i>+PB) in triplicates. Comparison of the same parameter among groups: ANOVA (Osmolality, p<0.0001; Creatinine, p<0.0009; Uric acid, p<0.005; Urea, p = 0.06; Protein, p<0.001). Post hoc Student-Newman-Keuls (different letters over the bars indicate statistical differences: osmolality and creatinine, p<0.01; uric acid and protein, p<0.05).</p

Assessment of lethality after treatments.

<p>Mice treated intraperitoneally (ip) and/or <i>per oral</i> (po) with vehicle (control), allopurinol (NL), probenecid (PB) and <i>Crotalus durissus terrificus</i> venom (<i>vCdt</i>) followed by NL (<i>vCdt</i>+NL) or PB (<i>vCdt</i>+PB) after 2 h.</p><p>*Lethality at 24 h only differed in <i>vCdt</i>+PB (p = 0.0432) and <i>vCdt</i> (p = 0.0016) compared with all other groups. Lethality at 24 h did not differ between <i>vCdt</i>+PB and <i>vCdt</i> (p = 0.1811) (Two-sided Fisher's exact test).</p

Histopathological features of renal samples.

<p>Slides of hematoxilin-eosin stained sagittal sections from representative kidneys of mice treated with: <b>I</b> and <b>II</b>: vehicle (control); see normal appearance of Bowman's capsule (<b>BC</b>), glomerulus (<b>G</b>), macula densa (<b>DM</b>) and distal tubule (<b>DT</b>); <b>III</b>, <b>IV</b> and <b>V</b>: <i>C. d. terrificus</i> venom; the most frequently changes detected were edema (<b>*</b>), fibrosis (<b>1</b>) with cell influx (<b>2</b>), and tubular necrosis with tubules markedly dilated and cellular debris in the lumen (<b>3</b>, <b>4</b>) and in the brush border (<b>BB</b>). Treatments of envenomed with allopurinol or probenecid acted indistinguishably to ameliorate the frequency and the intensity of detectable histological changes comparatively with untreated envenomed mice. Bars = 100 µm.</p

Effects of treatments on hematocrit and renal function parameters in the blood plasma.

<p>Mice treated with vehicle (control), allopurinol (NL), probenecid (PB) and <i>Crotalus durissus terrificus</i> venom (<i>vCdt</i>) followed by NL (<i>vCdt</i>+NL) or PB (<i>vCdt</i>+PB) after 2 h. Values are means ± SEM. Number of animals in parentheses. Comparison of the same parameter among groups: ANOVA (Hematocrit, p = 0.1807; Osmolality, p = 0.3577; Creatinine, p<0.006; Uric acid, p<0.0001; Urea, p<0.003; Protein, p<0.0001). Post hoc Student-Newman-Keuls (different letters over the bars indicate statistical differences: creatinine and urea, p<0.05; uric acid and protein, p<0.01).</p