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Heat shock proteins and glucose-regulated proteins represent an extraordinary mechanism of defense induced in the kidney by chemicals or drugs and essential to survive. Here we resume our experience on the presence and regulation of stress proteins into acute and chronic nephrotoxic models in rodents and in vitro. In acute renal damage, induced in rats by a single injection of inorganic mercury, stress proteins enhanced in a dose-dependent manner to recover cytoskeleton and mitochondria and maintain nuclear activity. When we pre-treated mercury injected-rats with antioxidant melatonin or with bimoclomol, a stress proteins-coinducer, stress proteins expression was modulated together with tubular recovery. Similar data were obtained in ischemia-reperfusion in rats treated with stannous chloride, that provided cytoprotection stimulating heme oxygenase induction. During nephrotoxicity induced by administration of cyclosporine A at therapeutic dosage for 1-2 months, stress protein overexpression well correlated with oxidative and cell death, but decreased if we counteracted renal damage using antioxidants. In aluminium intoxication through drinking water for 3-6 months, we detected a time-dependent stress response in the rat kidney that was organ specific and different from the liver. In vitro studies on rat tubular proximal cells exposed to heavy metals demonstrated that stress protein expression was related to peculiar mechanisms of action of each metal. In conclusion, experimental studies on the renal chaperones can greatly contribute to understand their role, and agents able to modulate the stress response might be considered promising therapeutic tools to reduce nephrotoxicity.

Proximal tubular reabsorption was studied by the split drop micropuncture technique in HgCl2-induced severe as well as mild acute renal failure. 4 mg/kg of HgCl2 given subcutaneously to normal rats resulted in severe and usually oliguric acute renale failure at 48 h, mean plasma creatinine and urea having risen to 6.9 +/- 0.4 and 420 +/- 30 mg%. On inspection of the kidney surface, usually more than 50% of the convolutions appeared white opaque and collapased. Split drop reabsorption of 0.9% NaCl, 20% mannitol and 20% albumin was markedly accelerated in these necrotic tubular segments, while reabsorptive rates were usually quite reduced in the normal-looking red transparent convolutions. DOCA/saline-pretreated rats developed mild renal failure, with plasma creatinine and urea rising slightly to 1.6 +/-0.3 and 83 +/- 14 mg%, respectively, at 48 h after 4 mg/kh HgCl2. Reabsorptive rates were almost uniformly reduced from 0.55 +/- 0.02 in controls to 0.32 +/- 0.03 nl-mm-2 sec-1 in mild HgCl2-induced acute renale failure. Mild proximal tubular injury features decreased reabsorptive rate while severely damaged tubules appear to be leaky to the extent of allowing rapid disappearance from the tubular lument of the normally barely reabsorbable 20% albumin. Although compatible with unrestricted passive backflow being an additional factor in the pathogenesis of HgCl2-induced acute renal failure, these results do not challenge the importance of primary filtration failure.

Intrarenal haemodynamics and glomerular dynamics have been investigated in dogs with mercuric chloride-induced acute renal failure. The early phase (12 and 24 hr after the intravenous injection of 2 mg/kg HgCl2) is characterized by some decrease in renal bloodflow, due to afferent (preglomerular) vasoconstriction, while in the later phase (48 and 72 hr after poisoning a pronounced increase in RBF due to efferent (postglomerular) vasodilatation supervenes. Urinary volumes amounts to normal in the early phase, followed by oligo-anuria in the 48 and 72 hr groups. Extraction ratio of inulin, i.e. the filtration fraction and, consequently, glomerular filtration rate show a progessive decline and trend towards zero in the 72 hr group. The pronounced decrease in glomerular capillary pressure is due to both absolute and relative increase and decrease in afferent and efferent resistances, repectively. The progressive fall in effective filtration pressure is brought about by the decrease of glomerular capillary pressure, combined with increased colloid osmotic pressure due to haemoconcentration. Total and segmental intrarenal vascular resistances are reduced by hyperosmotic mannitol infusions resulting in renal hyperaemia. Glomerular filtration rate is, however, not influenced by mannitol and effective filtration pressure remains unaltered. Osmotic diuresis ensues in the early phase but urinary output is not restored in the late, i.e. oligo-anuric, phase.

Histologic evidence of intrarenal vasomotor changes were observed in the rat in the course of acute renal failure caused by the injection of HgCl2. Male Wistar rats injected s.c. with 2.5 or 4.7 mg HgCl2 per kg b. wt. developed fibrinoid damage in the media segments of preglomerular renal vessels, mostly in the arcuate and interlobular arteries. The lesions were patchy and irregularly scattered throughout the kidneys. 24 h post-injection the lesions were very rare and of only mild degree, whereas they were fully developed and regularly seen 48 h post-injection. A high percentage of similar changes was found in certain extrarenal vascular areas especially in the mesentery and pancreas. The damaged vascular segments were usually dilated. The results of various thichrome stains and histochemical reactions suggested edema of vascular smooth muscle cells and imbibition of the media by blood plasma substances, sometimes reaching the degree of fibrinoid necrosis. These findings were confirmed by electron microscopy. The imbibition of the smooth muscle cells by blood plasma material was clearly evidenced by the demonstration of intracellular fibrin precipitations. In connection with the degeneration of smooth muscle cells, accumulations of crystal-like fibrin formations could often be shown. Subendothelial fibrin formations were not observed. 96 h after the 2.5 mg injection the changes were already regressing, but edema of the vascular wall and signs of disturbed vasotonia persisted for several days. The maximum of the vascular changes usually coincided with the maximum of azotemia and the formation of debris cylinders in the renal tubules. However, no clear relationship was recognizable in individual cases between vascular damage, extent of tubular necrosis and renal function. The pathogenesis of the vascular changes is obscure, but neurogenic factors, increased release of catecholamines and/or vasoactive agents of renal origin in connection with other factors might play a decisive role. Arterial hypertension was absent. It is assumed that the structural damage of the vascular media is mainly brought about by prolonged or recurring vasospasms, or by alternating spasm and vasodilatation with local ischemia and increased tension of the vascular wall in the dilated segments. The altered function and structure of the vascular wall might, to a certain extent, contribute to renal insufficiency.

Acute renal failure was induced in male rats by the subcutaneous injection of 4 mg HgC12 per kg body weight. Changes in the proximal tubule were studied by light and electron microscopy at six time intervals from 15 min to 24 h. Renal function was monitored at 6 and 24 h. Between 15 min and 3 h changes were similar in all regions of the proximal tubule (pars convoluta and pars recta). Dispersion of cytoplasmic polysome groups was widespread and mitochondrial matrices were condensed in some cells. No changes were noted in the brush border but increased endocytotic activity occurred in some convoluted tubules at 1 and 3 h. At 6 h severe changes had occurred in the pars recta in the medullary rays. Microvilli of the brush border were focally absent, the mitochondria were swollen and the endoplasmic reticulum was dilated. At this time only subtle changes occurred in the pars recta in the outer stripe of the outer medulla. However by 24 h necrosis was widespread throughout the pars recta, yet changes in the proximal convoluted portion were minimal. A significant azotemia, decreased GFR and increased FENa+ and FEK+ occurred at 6 and 24 h after HgC12 injection. Thus HgC12 at 4 mg per kg body weight produced reproducible renal failure and necrosis involving the pars recta of every nephron but necrosis did not begin in the pars recta until after 6 h while acute renal failure was probably initiated much earlier. The following hypothesis is presented. HgC12 initially interacts with the entire proximal tubule. Although injury is sublethal in the pars convoluta it is responsible for greatly diminished sodium reabsorption and is related to the pathogenesis of the renal failure through feedback mechanisms involving the macula densa and release of renin. This results in renal hemodynamic alterations, decreased GFR and other functional disturbances associated with renal failure. The development of necrosis in the pars recta appears to be a relatively late event, possibly due to further accumulation of Hg++ in this region. In any case, the necrosis appears pathogenetically dissociable from the mechanism of acute renal failure.

Renal cortical blood flow of rats with postischemic, myohemoglobinuric, and mercury-induced acute renal failure was measured by the hydrogen washout technique using implanted platinum electrodes. Total renal blood flow was determined by venous cannulation in separate series of rats. The values obtained with the two methods were in excellent qualitative agreement (r=0.99, P less than 0.001), although venous cannulation gave values that were constantly lower than those calculated for whole kidney from the cortical flow rate and assumed cortical mass. Myohemoglobinuria produced by glycerol injection caused cortical blood flow to fall from a control value of 7.37+/-0.23 (SEM) ml/min X g of cortex to approximately one-half that value for four hours after injection (P less than 0.001). Flow rates 12 and 24 hr after glycerol injection were 85% (P less than 0.001) and 90% (P less than 0.05) of control, respectively. Cortical flow was reduced to 5.49+/-0.39 (SEM) ml/min X g of cortex four hours after release of one hour's total bilateral renal arterial occlusion (P less than 0.001), but rose to normal within 24 hr. Poisoning with 4.7 mg/kg of body wt of mercuric chloride produced a cortical blood flow value that was 30% higher than control 24 hr after injection (P less than 0.01), while a 12 mg/kg of body wt dose gave a normal flow value. Inulin clearance was severely depressed in all models at all study times. Thus, in contrast to human acute renal failure, marked renal cortical ischemia is not an essential feature of these different forms of murine acute renal failure.

Experiments were conducted to determine if administration of the sulfhydryl reducing agent and metal chelator dithiothreitol (31 mg/kg body wt) alters the development of renal dysfunction in the first 3 hr after injection of mercuric chloride (3 mg/kg). Mercuric chloride alone resulted in elevation of urine flow rate and fractional excretion of solutes within 30 min of injection. In animals injected with dithiothreitol 60 min after mercuric chloride, urine flow rate and fractional excretion of solutes were reduced within 30 min to values intermediate between control and mercuric chloride-treated rats. Neither the injection of mercuric chloride alone nor when followed by dithiothreitol resulted in changes in mean arterial blood pressure or glomerular filtration rate. In addition, dithiothreitol did not reduce urine flow rate or fractional excretion of solutes when these parameters were elevated during extracellular fluid volume expansion. Measurement of mercury in organs of those rats injected with mercuric chloride alone or prior to dithiothreitol revealed no alteration in organ distribution. The renal cortex contained the highest concentrations of mercury, and these concentrations were comparable in both groups of rats. These studies demonstrate that dithiothreitol can ameliorate the renal toxicity of mercury and suggest that this effect is mediated through an intrarenal site of action.