Alteration of hepatocellular structure and function by thallium chloride: ultrastructural, morphometric, and biochemical studies.

The effects of thallium chloride (TlCl3.4H2O) on hepatocyte structure and function were studied in male rats at 16 hr following treatment by ip injection with doses of 0, 50, 100, and 200 mg/kg. Ultrastructural examination of hepatocytes from thallium-treated rats showed a dose-related loss of ribosomes from the endoplasmic reticulum and proliferation of the rough endoplasmic reticulum segment. Generalized mitochondrial swelling and increased numbers of electron-dense autophagic lysosomes were also observed. Morphometric analysis of hepatocytes from thallium-treated rats disclosed a 3-fold increase in the volume density of the lysosomal compartment and a 1.3-fold increase in the volume density of mitochondrial. Surface density measurements of mitochondrial and endoplasmic reticulum membranes showed dose-related increases in the surface density of both inner and outer mitochondrial membranes as well as of the rough endoplasmic reticulum. These structural changes were associated with pronounced increases in the specific activities of the mitochondrial membrane-associated enzymes monoamine oxidase and ferrochelatase to 145 and 144% of control values, respectively, and a 42% decrease in the activity of aminolevulinic acid (ALA) synthetase. Similarly, structural alteration of the endoplasmic reticulum in thallium-treated rats was associated with concomitant impairment of the microsomal enzymes NADPH cytochrome c (P-450) reductase, aniline hydroxylase, and aminopyrene demethylase to a maximum of 49, 43, and 77% of activities seen in untreated controls, respectively. In contrast, the non-membrane-bound enzymes malate dehydrogenase, ALA dehydratase, and uroporphyrinogen I synthetase were unaltered in vivo following thallium treatment at any doses. These results indicate that thallium-induced alteration of hepatic biochemical processes may arise from physical disruption of the membranal integrity of subcellular organelles with which those processes are functionally associated. These findings are consistent with those from previous studies in demonstrating a positive quantitative correlation between metal-induced subcellular organelle membrane structural injury and impairment of associated biological functions in vivo.