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Toxicological studies in adult amphibians: Effects of lead

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This paper summarises the results of studies that examined the biochemical and physiological effects of lead (Pb) in an in vivo amphibian model (the South American toad Bufo arenarum) under laboratory conditions. Acute toxicity tests generated LD50s that indicated a high tolerance to Pb. In animals injected intra-lymphatically with a sublethal dose of Pb, the total numbers of red (RBC) and white blood cells (WBC) and differential leukocytes were altered in a dose-related fashion. RBC osmotic fragility was also affected; i.e. the concentration of NaCl necessary to provoke 50% haemolysis was significantly reduced in lead-injected toads, indicating an increase in the osmotic resistance of the cells. Other studies examined δ-Aminolevulinic acid dehydratase (δ-ALAD) activity, free erythrocyte protoporphyrin (FEP) levels and blood Pb. FEP and blood Pb were shown to be valuable biomarkers of chronic metal intoxication, the former being the marker with the highest sensitivity. In lead injected animals FEP increased almost 9-fold compared to controls. The highest concentration of Pb occurred in the liver at a level 382 times higher than the controls. Kidney, spleen, and femur also appeared as repository sites of the metal, although in lower proportions. Other studies examined immunocompetency parameters. Lead affected the function of the polymorphonuclear cells of B. arenarum. Phagocytic and lytic functions of the adherent blood cells incubated with suspensions of Candida pseudotropicalis were negatively affected after the lead administration. The decrease of the phagocytic activity was statistically correlated with blood Pb levels. Also, following administration of Pb the production of natural antibodies was significantly increased by 39%. In non-exposed control animals there was a non-significant increase. It was concluded that in B. arenarum Pb may act as an immunostimulating factor on the humoral immune system. Serum protein electrophoresis was performed. Administration of Pb provoked a significant decrease in both total proteins and the albumin fraction. Among the globulin fractions, the G3 fraction was augmented. These findings were interpreted as a consequence of Pb toxicity on toad hepatic cells, the kidney and some components of the immune system.


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