Light and electron microscopic observations of the acute sublethal hepatotoxic effects of Mirex in the rat.

The fire-ant poison, Mirex, was administered via stomach tube (dosage 200 mg/kg) to 50 adult Mai-Wistar male rats and the resultant histopathologic lesions produced in their livers after six days post-intubation are described. Light (LM) and electron microscopic (EM) technques revealed cellular and subcellular alterations in response to this sublethal dosage. Pathologic lipid accumulations occurred in Mirex-exposed rats and this fat appeared in a distinctive periportal zonation pattern. Additional lesions were detected in centrolobular zones with the EM and included severe glycogen depletion, altered regularity in the architecture of rough or granular endoplasmic reticulum (GER), dilated GER cisternae, free ribosomes, and proliferation of smooth endoplasmic reticulum. Periportal hepatocytes exhibited apparent reduction in numbers of cytoplasmic organelles and development of many, large lipid-containing vacuoles. Myelin figures were sometimes associated with developing lipid (liposomes), suggesting a contribution of myelin membranes to the developing lipid droplets or vice versa. Biochemical studies revealed that glycogen levels dropped markedly, lipid content greatly increased, and protein/DNA and RNA/DNA values decreased.