Assessment of functional, morphological, and enzymatic tests for acute nephrotoxicity induced by mercuric chloride

The relative merits of a comprehensive series of contemporary methods for detection of acute nephrotoxicity were evaluated. Male Sprague-Dawley rats were given 0, 0.25, 0.5, 1.0, or 3.0 mg mercuric chloride (HgCl2)/kg body weight by ip injection. Indices of nephrotoxicity were examined 8, 24, 48, 72, and 96 h later. Alterations in urine osmolality, volume, and protein levels were seen within 24 h in response to 1 mg/kg or more of HgCl2. Administration of 0.5-3.0 mg/kg produced dose-dependent increases in urinary excretion of maltase activity and glucose by 24 h, the period of peak effect. There was no increase in maltase or alkaline phosphatase (AP) activity in the serum of these animals. Enzymuria was not apparent in rats that had marked elevations in serum AP, argininosuccinate lyase, and ornithine carbamyl transferase activities as a result of physical (i.e., dichlorodifluoromethane-frozen) or chemical (carbon tetrachloride-induced) damage of the liver. Morphological alterations, in the proximal tubular epithelium of perfusion-fixed kidneys from HgCl2-dosed rats, paralleled the changes in enzyme excretion with respect to time of onset and dose-effect. There was a dose-dependent inhibition of tetraethylammonium (TEA) and p-aminohippurate (PAH) uptake by renal cortical slices at 24 h. Interestingly, increases in uptake of TEA and PAH were seen 8 h after a 1-mg/kg dose. Clearance of inulin and PAH in vivo were altered at 8 h by 0.5 and 1 mg/kg. Marked depression of these functional indices was seen at 24 h, by which time blood urea nitrogen (BUN) levels were increased. The 0.5- and 1.0-mg/kg doses also produced time- and dose-dependent increases in intracellular Na+ content which were maximal at 24 h. These results illustrate the importance of using a combination of biochemical and functional tests to elucidate the sequence of events in the kidney following toxic insult. Nevertheless, some of the simpler, traditional techniques (e.g., histopathology, urinalyses, BUN) were sensitive and organ-specific, and should continue to be very useful in nephrotoxicity testing/screening.