ZINC-AND OR CADMIUM-INDUCED INTESTINAL METALLOTHIONEIN AND COPPER-METABOLISM IN ADULT-RATS/

Feeding diets with high zinc or cadmium concentrations to animals comp romises their copper status. Previous work suggested that metallothion ein (MT), induced in the intestinal mucosa by zinc or cadmium, binds c opper and inhibits its absorption. More recent studies showed that thi s mechanism may not be operative for zinc and that intestinal MT adapt s to long-term feeding of high-zinc diets. The present study ws design ed to determine the effects of feeding high-zinc and/or high-cadmium d iets on the induction of intestinal MT and its subsequent effects on c opper status. Six-week-old male rats were placed in a 2 x 2 x 3 factor ial experiment with two concentrations of dietary zinc (60 and 350 mg/ kg), two concentrations of dietary copper (3 and 9 mg/kg), and three c oncentrations of dietary cadmium (0, 1 and 5 mg/kg). After 3 weeks, th e difference in the MT concentration between rats fed high- and normal -zinc diets was only 1.5 times. However, rats fed the highest amount o f cadmium had MT concentrations about five time higher than those thos e mot fed cadmium. In both the zinc and cadmium groups, the concentrat ion of intestinal zinc and cadmium followed that of MT; however, the c opper concentration were not changed. Although intestinal MT was not e levated appreciably in zinc-fed rats, the copper status of these rats fed 3 mg of copper/kg of diet was severely depressed. Rats fed 9 mg of copper/kg were not affected. The copper status in rats fed high-cadmi um and 3 mg of copper/kg of diet was depressed even more than the resu lt of induced intestinal MT binding of copper thus preventing its pass age into the circulation.