Accumulation and depletion of zinc in rat liver and kidney metallothionens.

The accumulations of zinc in liver and kidneys of rats fed various dietary levels of this element was investigated. Zinc started to accumulate in rat liver when 1,000 ppm or higher levels of this element were fed in the diet, but not when the dietary zinc level was 500 ppm less. Almost all of the accumulated zinc in the soluble fraction was found to be present in the metallothionein (MT) fractions. When rats were fed a diet supplemented with 2,000 ppm, zinc, the metal rapidly accumulated in MT in the liver and kidneys. The accumulated zinc was, however, depleted to the pre-supplementation level after only 3 days of feeding a zinc deficient diet. While rats were fed the zinc deficient diet, in which the element was simultaneously depleted from MT, significant increased excretion of the metal occurred in the feces urine. No evidence was found to indicate that zinc was excreted in the bile in association with MT. It was therefore concluded that MT is probably, as one of its possible biological roles, more involved in accumulation of excessive zinc rather than in storage of the metal for later utilization.