Subcellular distribution of lead in cultured rat hepatocytes

Exocrine cell mitochondria of the rat pancreas after lead intoxication

The aim of the study was to evaluate alterations in exocrine cell mitochondria of the rat pancreas after lead acetate intoxication. The experiment used 45 rats divided into 2 experimental groups receiving lead acetate to drink, of lead concentration 50 and 500 mg/dm3 (ppm), and a control group given tap water. The animals from the experimental group were decapitated after 2, 4, 6 and 8 weeks, 5 rats from the control group after 8 weeks of the experiment. Rats from experimental groups decapitated after 8 weeks had lead administration stopped after six weeks and then, for two weeks tap water was given. Pancreatic sections were examined with biochemical methods for the activity of cytochrome oxidase and succinic dehydrogenase. Ultrastructural and morphometric examinations were also performed. It was demonstrated that: a) exocrine cell mitochondria are particularly predisposed to lead effect, b) intoxication of rats with lower lead doses (50 ppm) causes reversible adaptative or compensatory changes in these organelles, c) intoxication of rats with higher lead doses (500 ppm) induces irreversible ultrastructural alterations in numerous mitochondria, including damage to inner and to outer mitochondrial membranes, d) structural changes in the mitochondria in the course of lead intoxication are the morphological expression of the impairment of metabolic processes, associated with the inhibited activity of the respiratory enzymes: succinic dehydrogenase and cytochrome oxidase.

Increased lead uptake and inhibition of ALAD-activity in isolated rat hepatocytes incubated with lead-diethyldithiocarbamate complex

Dithiocarbamates can form lipid soluble complexes with lead and are known to markedly increase tissue uptake of lead and potentiate toxic effects of lead in rats. Cellular effects of the interactions between lead and diethyldithiocarbamate were studied in primary cultures of rat hepatocytes. The cells were incubated with lead acetate (PbAc) or lead-diethyldithiocarbamate complex (Pb(DTC)2), labelled with 203Pb. The lipid soluble Pb(DTC)2 was rapidly taken up in the cells and after 30 min incubation the cellular levels of lead were approximately 40 times higher in cells incubated with Pb(DTC)2 than in cells incubated with a similar concentration of PbAc. The maximal cellular uptake of lead was reached after 4 h incubation with Pb(DTC)2, while incubation with PbAc caused a slow continuously increasing uptake of lead during the 20 h incubation. The enzyme delta-aminolevulinic acid dehydratase (ALAD) was inhibited to a much higher extent by Pb(DTC)2 compared to PbAc after incubations with similar concentrations of lead. Maximal inhibition of ALAD activity was reached at a cellular concentration of 0.5-1 nmol Pb/mg protein, irrespective of which form of lead was used in the incubation. Pb(DTC)2 was shown to inhibit ALAD activity also in vitro when incubated with purified ALAD enzyme. The rapid and high intracellular uptake and cellular response of Pb(DTC)2, shown in the present study, may explain the drastic effects of dithiocarbamates on lead distribution and toxicity previously shown in vivo.