Endogenous antioxidant defence system in rat liver following mercury chloride oral intoxication

Mercury is a highly toxic metal which induces oxidative stress. Superoxide dismutases, catalase, and glutathion peroxidase are proteins involved in the endogenous antioxidant defence system. In the present study rats were administered orally, by gavage, a single daily dose of HgCl2 for three consecutive days. In order to find a relation between the proteins involved in the antioxidant defence and mercury intoxication, parameters of liver injury, redox state of the cells, as well as intracellular protein levels and enzyme activities of Mn-dependent superoxide dismutase (MnSOD), Cu-Zn-dependent superoxide dismutase (CuZnSOD), catalase, and glutathione peroxidase (GPx) were assayed both in blood and in liver homogenates. HgCl2 at the doses of 0.1 mg/kg produced liver damage which that was detected by a slight increase in serum alanine aminotransferase and gamma glutamyl transferase. Hepatic GSH/GSSG ratio was assayed as a parameter of oxidative stress and a significant decrease was detected, as well as significant increases in enzyme activities and protein levels of hepatic antioxidant defence systems. Changes in both MnSOD and CuZnSOD were parallel to those of liver injury and oxidative stress, while the changes detected in catalase and GPx activities were progressively increased along with the mercury intoxication. Other enzyme activities related to the glutathione redox cycle, such as glutathione reductase (GR) and glucose-6-phosphate dehydrogenase (G6PDH), also increased progressively. We conclude that against low doses of mercury that produce a slight oxidative stress and liver injury, the response of the liver was to induce the synthesis and activity of the enzymes involved in the endogenous antioxidant system. The activities of all the enzymes assayed showed a rapidly induced coordinated response.