RESUMO
This study investigated the activity of lactated dehydrogenase (LDH), malate dehydrogenase (MDH) enzymes and the levels of glucose, protein and triglyceride in bullfrog tadpoles after exposure to 1 µg L-1 of zinc (Zn), copper (Cu) and cadmium (Cd) isolated and combined for 2 and 16 days. Zn, Cu + Cd and Zn + Cu + Cd increased the activity of the LDH (2 and 16 days) and MDH (2 days) enzymes in the liver; and MDH increased in the kidney after 16 days in all co-exposed groups compared to the control. Glucose increased in the liver in the Zn and Cu groups at 2 and 16 days of exposure and decreased in the kidney (groups Cd, Zn + Cd and Cu + Cd) and muscle (Cd) at 2 days of exposure. After 2 days of exposure, the protein increased in the liver (Zn), in the kidney in all groups exposed to metals except in the groups exposed to Cd and Zn + Cu + Cd, which did not change and decreased in muscle in all the groups exposed to isolated metals. Regarding triglycerides, the kidney and muscle were the most affected, leading to a decrease in the Zn, Cu and Cd groups and in the Zn + Cu (16 days) and Zn + Cu + Cd groups (2 days). The anaerobiosis and aerobiosis were activated in the liver and kidney after short-term exposure (2 days) and in the kidney, the aerobic metabolism was activated after chronic exposure (16 days). The metals caused toxicity and were higher in co-exposure to metals with a potential to cause metabolism damage in L. catesbeianus.