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 eczema, at either 12 g ZnO fortnight-1 or 12 g ZnO week-1, and the effect of Zn on MT-Ia and -II mRNA expression in liver, kidney, duodenal, muscle and skin tissue was compared with those of untreated animals. Tissue concentrations of Cu, iron (Fe), manganese (Mn) and Zn were determined by plasma emission spectrometry. Metallothionein-Ia and -II mRNA concentrations were 4 to 9-fold greater in the liver and kidney of dosed sheep compared with untreated animals, but not higher in duodenal, mucscle or skin tissue. Zinc concentrations increased in all tissues, except skin, and were strongly correlated with MT expression. Copper uptake into tissues was not inhibited and it was concluded that this was because duodenum tissue MT mRNA expression was not greatly affected. Relationships between MT-mRNA, MT in liver, and Zn and Cu tissue concentrations are presented and discussed.

Romney wether sheep were given ZnO on a regular basis, as required in protocols for the treatment of facial eczema, at either 12 g ZnO fortnight-1 or 12 g ZnO week-1, and the effect of Zn on the synthesis of different metallothionein (MT) isoforms isolated from liver tissue characterized and quantified. Metallothionein isoforms in liver of dosed and non-dosed sheep were quantitatively determined by reverse phase HPLC, with markedly increased concentrations of total MT-Ia protein found in the liver tissue of Zn-dosed groups (634 pg g-l fresh weight for the weekly dosed group) compared with 49 pg g-1 fresh weight in non-dosed sheep. The concentration of MT-II protein was not significantly increased. Individual sheep varied widely in the relative amounts of each MT isoform expressed with increased amounts of types of MT-Ia especially, and MT-I1 in some animals, which bound predominantly Cu. The half-lives for [35S]-cysteine and 67Zn in MT isoforms from weekly dosed sheep were found to be 2.5-3.5 days and 5-24 h respectively, indicating relatively fast exchange of Zn with MT compared with synthesis. Rate of synthesis for MT-Ia was twice that for MT-11. Data reflecting relationships between MT isoforms, Cu and Zn concentrations in liver are presented and discussed.