METALLOTHIONEIN AND TRACE-ELEMENT METABOLISM IN SHEEP TISSUES IN RESPONSE TO HIGH AND SUSTAINED ZINC DOSAGES .2. EXPRESSION OF METALLOTHIONEIN M-RNA

Increased dietary zinc (Zn) influences metallothionein (MT) expression in sheep, which in turn effects changes in the regulation of both Zn and copper (Cu) tissue uptake. Romney wether sheep were given ZnO on a regular basis, as required in protocols for the treatment of facial e czema, at either 12 g ZnO fortnight(-1) or 12 g ZnO week(-1), and the effect of Zn on MT-Ia and -II mRNb expression in liver, kidney, duoden al, muscle and skin tissue was compared with those of untreated animal s. Tissue concentrations of Cu, iron (Fe), manganese (Mn) and Zn were determined by plasma emission spectrometry. Metallothionein-Ia and -II mRNb concentrations were 4 to 9-fold greater in the liver and kidney of dosed sheep compared with untreated animals, but not higher in duod enal, muscle or skin tissue. Zinc concentrations, increased in all tis sues, except skin, and were strongly correlated with MT expression. Co pper uptake into tissues was not inhibited and it was concluded that t his was because duodenum tissue MT mRNA expression was not greatly aff ected. Relationships between MT-mRNA, MT in liver, and Zn and Cu tissu e concentrations are presented and discussed.