Induction and Accumulation of Metallothionein in Liver and Pancreas of Chicks Given Oral Zinc: A Tissue Comparison

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Abstract
The present study was undertaken to compare apparent zinc metabolism in two organs, the liver and pancreas. Four-week-old chicks received an oral dose of saline or an equal volume of zinc solution containing 4, 8 or 16 mg zinc. The accumulation of zinc metallothionein (MT) was determined 24 hours postgavage in hepatic and pancreatic cytosol. The rate of MT synthesis was determined in both tissues by a pulse labeling technique. In response to orally administered zinc, plasma zinc increased sharply (by 3 hours) and in proportion to the amount of zinc given. At 12 hours there was little difference in plasma zinc. The concentration of zinc MT in pancreatic cytosol relative to liver was nearly fivefold higher in control chicks and increased at approximately twice the rate when chicks were given zinc. Despite this marked difference in both the rate and extent of zinc MT accumulation there was little evidence of a difference in the rate of MT synthesis. Quantitation of MT by anion-exchange chromatography demonstrated an apparent maximum in the rate of MT synthesis at 6 hours, which was apparently the same in pancreas and liver. Our data suggest that when compared to liver, the pancreas possesses a markedly higher concentration of MT-bound zinc and a greater propensity to accumulate zinc MT when zinc status is acutely elevated. This tissue difference appeared not be be due to a greater capacity to synthesize MT.