Metallothionein and trace element metabolism in sheep tissues in response to high and sustained zinc dosages. 2. Expression of metallothionein m-RNA

Abstract

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.

The potential for increasing the concentrations of micro-nutrients relevant to human nutrition in meat, milk and eggs

“…In sheep, one study (Lee et al . 1994) found a significant increase in muscle Zn in response to herbage Zn, while in another Henry et al . (1997) reported a decrease.…”

“…In depletion studies in pigs (Shaw et al 2002;Hernández et al 2008), muscle Zn concentrations remained unchanged, while liver and kidney Zn were depleted. Supplementation with varying forms of Zn in cattle (Malcolm-Callis et al 2000;Kessler et al 2003), sheep (Lee et al 1994;Rojas et al 1995;Henry et al 1997) and chickens (Bou et al 2004(Bou et al , 2005 had little effect. In sheep, one study (Lee et al 1994) found a significant increase in muscle Zn in response to herbage Zn, while in another Henry et al (1997) reported a decrease.…”

“…Supplementation with varying forms of Zn in cattle (Malcolm-Callis et al 2000;Kessler et al 2003), sheep (Lee et al 1994;Rojas et al 1995;Henry et al 1997) and chickens (Bou et al 2004(Bou et al , 2005 had little effect. In sheep, one study (Lee et al 1994) found a significant increase in muscle Zn in response to herbage Zn, while in another Henry et al (1997) reported a decrease. Similarly, egg (Skrivan et al 2005) and milk Zn (Cope et al 2009) were unresponsive to dietary supplementation.…”

Pasture Soils Contaminated with Fertilizer-Derived Cadmium and Fluorine: Livestock Effects

“…However, while Zn fed to sheep reduced the net accumulation of Cd in liver, it increased accumulation in kidney (Lee et al 1991;Rounce et al 1998). The accretion of Cd in the kidneys with high Zn doses has been associated with increased MT synthesis, which improved the effi ciency of the kidney to sequester Cd (Bremner 1978;Lee et al 1994;Peterson and Mercer 1988).…”