Regulation of Heme Oxygenase Activity in Rat Liver during Oxidative Stress Induced by Cobalt Chloride and Mercury Chloride

Activities of heme oxygenase and tryptophan-2,3-dioxygenase and cytochrome P450 content in liver as well as absorption of the Soret band and optical density at 280 nm in serum were determined 2 and 24 h after administration of HgCl₂ and CoCl₂ and after co-administration of the metal salts with a-tocopherol. Administration of HgCl₂ and CoCl₂ increased the contents of hemolysis products in the serum, induced heme oxygenase, and decreased cytochrome P450 content in the liver. Injection of HgCl₂ increased the activity of tryptophan-2,3-dioxygenase holoenzyme and enzyme saturation with the heme, but administration of CoCl₂ decreased these parameters. Pretreatment with a-tocopherol completely blocked the changes induced by HgCl₂ after 24 h. Induction of heme oxygenase induced by CoCl₂ was not blocked by a-tocopherol, but this antioxidant normalized the increase in the level of hemolysis products in the serum and decrease in tryptophan-2,3-dioxygenase holoenzyme activity and cytochrome P450 content. Mechanisms of regulation of heme oxygenase by mercury and cobalt ions are discussed.