The effect of dietary zinc status on biliary metal excretion of rats

The effect of dietary zinc status on biliary excretion of zinc, cadmium and mercury administered as a bolus of metal chloride (1 mg metal/kg body weight i.v.) was studied. Female rats were fed a purified diet containing either 9 μg/g (low), 45 μg/g (adequate) or 1150 μg/g (high) zinc for 8 d. Hepatic metallothionein (MT) was similar in low- and adequate-zinc groups, but was 18-fold higher in the high-zinc group than in the other two groups. Liver zinc content varied in relation to dietary zinc level. Biliary excretion of all metals studied was significantly lower in the high-zinc group than in the low-zinc group. The cumulative excretion of zinc, cadmium and mercury over 2.5 h in rats fed these two diets was 6.2 ± 1.4 vs. 33.5 ± 7.7, 0.006 ± 0.02 vs. 22.8 ± 8.4 and 1.6 ± 0.6 vs. 14.9 ± 5.3 μg/kg body weight, respectively. A relationship was found between the disposition of metal in liver and the extent of biliary metal excretion. Biliary metal excretion was highly correlated with liver cytosolic non-MT-bound metal; r = 0.999, 0.998 and 0.993 for endogenous + exogenous zinc, cadmium and mercury, respectively.