Biological function of metallothionein. V. Its induction in rats by various stresses

Induction of metallothionein (a Zn-binding protein) was investigated in liver and kidneys of rats under the following stresses: cold environment, hot environment, heat burn, strenuous exercise, and CCl4 intoxication. As markers of metallothionein (MT) synthesis, [14C]cystine and 65Zn were injected parenterally into rats, and MT in liver and kidney supernatants was separated on Sephadex G-75 columns. Among stresses tested, the greatest stimulations of MT synthesis in liver were observed under cold (315%), strenuous exercise (302%), and CCl4 intoxication (543%), as evidenced by increased amount of [14C]cystine and 65Zn incorporation into the MT fraction. In contrast to liver, only small responses were observed in MT synthesis in kidneys. There was a general decline in plasma Zn levels in rats under the stresses employed. However, no great differences were observed in Zn levels in whole liver and kidneys. The present study suggests that various unrelated physiological stresses, which are accompanied with a change in Zn distribution, increase the synthesis of MT in liver of rats.