Interactions of zinc and selenium on the binding of cadmium to rat tissue proteins

The administration of cadmium to rats by either oral or injection routes causes zinc to accumulate in the low molecular weight (MW) protein metallothionein (MT) of liver and kidney, but not in a low MW protein in the testis. Preliminary evidence indicates that the low MW cadmium-binding protein in testes is not MT. Feeding high levels of zinc to rats results in its accumulation with tissue MT, and the zinc is very labile. In contrast, the zinc that accumulates in MT as the result of cadmium exposure is not very labile. In the reverse situation, zinc does not cause cadmium to accumulate in MT. The turnover of MT is shorter when saturated with zinc than when cadmium is the predominant metal bound to it. Even though selenium will counteract testicular damage due to cadmium, it causes cadmium to accumulate in this organ at higher levels than in animals exposed to cadmium without selenium. Injection of selenate, and selenide--but not selenomethionine or selenocystine--diverts the binding of injected cadmium from low MW proteins to high MW ones in the testes. Selenium injections had only minor influences on the binding of zinc to testicular proteins. In contrast, very little diversion occurred in the binding of either cadmium or zinc in tissues of rats fed high levels of selenium. The data suggest that it is the selenide form of selenium that causes the diversion of cadmium binding in tissues, thus providing protection of testes against cadmium exposure.