INFLUENCE OF ZINC STATUS ON THE LEVELS OF METALLOTHIONEIN IN ISOLATED PERFUSED RAT-LIVER

The levels of cadmium and zinc metallothionein in isolated perfused livers of zinc depleted and repleted rats were investigated. Rats (160-200 g or 90-120 g) were fed either a zinc-deficient or zinc-supplemented diet for 62 or 42 days. The 90 to 120 g rats were repleted with 30 ppm Zn2+ in the drinking water for 1, 4 and 10 days after 35 days of depletion, and another group after depletion for 21 days was repleted for 15 days on a 21% casein diet. At appropriate times livers were cannulated, removed and perfused ± 25 μg Cd2+ as CdCl2, for 2 hours through the portal vein in a perfusion apparatus. Zinc depletion resulted in significant decreases in growth rate (1.4 versus 5.7 g/day) and liver weights. Repletion with Zn for 10 days increased the weight gain to 7.1 g/day. Depletion decreased the incorporation of Zn and Cd into metallothionein by 57 to 60%, while repletion for 1, 4 and 10 days increased the incorporation to nearly 500% of control levels. But, as repletion progressed, zinc in metallothionein fell to normal levels after 15 days. Cadmium in metallothionein did not decrease between 1 and 10 days of repletion. Zinc deficiency also reduced the zinc content of the liver by 44%, which increased to normal levels after 10 days of repletion. These data support the conclusion that zinc status can influence the incorporation of cadmium and zinc into metallothionein.