Effect of metal salts on UDPglucuronosyltransferase activity of various aglycones in rat liver microsomes in vitro.

The effects of aluminium, manganese, ferrous and ferric iron, cobalt, nickel, copper, zinc, cadmium, barium, mercury and lead ions on the rat hepatic UDPglucuronosyltransferase activity with regard to 4-methylumbelliferone, 4-nitrophenol, bilirubin, and 2-aminophenol were investigated in vitro. Conjugation of bilirubin was found to be activated by manganese, cobalt, nickel, cadmium, mercury and lead ions in native microsomes, but not in digitonin-treated microsomes. Aluminum, ferrous iron, cadmium, barium and lead increased the conjugation of 4-nitrophenol in native microsomes and aluminium in digitonin-treated microsomes as well. Lead slightly activated 4-methylumbelliferone conjugation, whereas none of the metal salts studied were found to activate the conjugation of 2-aminophenol. Copper and zinc salts inhibited all conjugations. In digitonin-treated microsomes, the conjugation of 4-nitrophenol was inhibited by cadmium and mercury, that of 4-methylumbelliferone by nickel and lead as well. The sensitivity of 4-methylumbelliferone conjugation to inhibition by mercury was most pronounced in microsomes prepared from rats pretreated with 2,3,7,8-tetrachlorodibenzo-p-dioxin.