Species differences in the hepatic response to mirex: Ultrastructural and histochemical studies

Abstract

Mirex was fed at levels of 1, 5, 15, and 30 ppm to mice, 5 and 30 ppm to rats, while monkeys received the chemical by stomach tube at levels of 0.25 and 1 mg/kg (equal to 5 and 20 ppm). Mice were killed and their livers obtained at 2, 4, 6, 9, 10, 15, and 18 months, whereas rats were killed and surgical biopsies were taken at 16, 19, 26, and 36 months. Cytochemical techniques were employed to detect activites of lysosomal β-glycerol phosphatase (ACpase) and glucose 6-phosphatase (G-6-pase). ACpase and G-6-pase remained unchanged and comparable to controls in livers of mice receiving 1 ppm. G-6-pase decreased in centrilobular areas while ACpase increased with time in the higher groups. At 12 months, liver cells that lost their G-6-pase activity surrounded by Kupffer cells that contained strong ACpase. In contrast, rat livers had no increase in ACpase and little loss in G-6-pase. Surprisingly, and in spite of the high levels of mirex ingested, monkey livers showed no loss of G-6-pase or activation of ACpase. Ultrastructurally, the underlying feature in all livers was proliferation of smooth endoplasmic reticulum (SER) displaying species variation. Thus, in mice, intense proliferation of SER that was both time- and dose-dependent was localized in specific regions of the cytosol. Hepatic cells, damaged and necrotic in mice fed 5, 15, and 30 ppm, were phagocytosed by activated Kupffer cells. SER proliferation in rat and monkey liver cells was less conspicuous than in mice. Except for this change, rat and monkey liver cells were normal. These studies emphasize species and enzyme variations in response to mirex. An interesting aspect observed was the lack of lysosomal catabolism during liver enlargement.