EFFLUX OF ENDOGENOUS ZINC LIBERATED FROM METALLOTHIONEIN AND ALCOHOL-DEHYDROGENASE IN THE LIVER BY REPLACEMENT WITH CADMIUM

Efflux of endogenous zinc (Zn) from the liver was examined to aid elucidation of the mechanisms of the discriminative uptake between the essential heavy metal Zn and the nonessential heavy metal cadmium (Cd). Cd was injected intravenously into rats with or without pretreatment of a small dose of Cd 6 or 24 hr earlier. The concentration of Zn in the whole liver decreased with time after Cd injection and the extent of the decrease was more apparent in the liver that contained the Zn bound to metallothionein (MT) by pretreatment. Time course curves of Cd and Zn in liver supernatants were identical to those of the corresponding whole livers, indicating that the changes observed in the whole livers were due to the changes in the supernatants. Distribution profiles of Cd and Zn by gel filtration chromatography indicated that Cd replaced Zn bound to both alcohol dehydrogenase (ADH) and MT. The decrease of Zn in the liver caused by Cd injection was explained by the efflux of the Zn liberated from ADH and MT, which suggests that efflux of Zn ions but not Cd ions occurs from the liver. The results are discussed from the viewpoint of discriminative uptake between Cd and Zn by the liver. © 1990.