Histopathology and cell proliferation induced by 2,2,4-trimethylpentane in the male rat kidney

Unleaded gasoline causes acute and chronic nephrotoxicity and renal tumors in male rats, but not female rats or mice of either sex. An active nephrotoxic component of unleaded gasoline has been identified as 2,2,4-trimethylpentane (TMP). The first objective of this study was to characterize light microscopic renal lesions induced in male F344 rats by a 21-day gavage regimen of 50 to 500 mg/kg TMP. The second objective was to localize and quantitate sites of renal cell proliferation induced by the same TMP dose regimens using histoautoradiographic analysis after [3H]thymidine incorporation. Light microscopic lesions in the proximal convoluted tubule consisted of protein droplet and crystalloid body accumulation, degeneration, and necrosis, and were similar to lesions noted in previous inhalation and gavage studies with other hydrocarbon compounds. The above renal lesions were not dose-related, although tubular dilation of thin limb segments with granular cell debris was dose-related. In cell proliferation studies TMP induced a non-dose-related five- to sixfold increase in the labelling index of the same proximal convoluted tubule portions (P2 segment) that contained severe crystalloid body accumulation, degeneration, and necrosis. Less pronounced, but statistically significant (p less than or equal to 0.05), increases in cell proliferation were also observed in other nephron segments, indicating a generalized regenerative response of the kidney to TMP. The cytotoxic and regenerative renal effects of TMP administered by gavage suggest that similar mechanisms may be involved in the induction of kidney tumors in male rats following chronic inhalation exposure to unleaded gasoline.