Accumulation and Depletion of Zinc in Chick Tissue Metallothioneins

Abstract

Two experiments were conducted with Hubbard broiler chicks on the metabolism of high levels of dietary zinc. In the first experiment, chicks were fed a basal diet or the basal diet plus 500, 1,000, 2,000 or 4,000 ppm zinc, and in the second experiment chicks were fed the basal diet or the basal diet plus 1,000, 2,000, 4,000, 8,000 or 16,000 ppm zinc, using zinc acetate. Zinc was found to be associated with 4 peaks when the cytosols from tissues (liver, kidney, pancreas and intestinal mucosa) were eluted through columns of G-75 Sephadex. Although the zinc content of all four peaks increased with increased zinc content of the diet, the greatest elevation occurred in metallothionein (MT). This protein was purified from all four tissues (liver, kidney, pancreas and intestinal mucosa) and the amino acid analysis revealed the presence of about 30% cysteine. Zinc accumulated to the greatest extent (microgram in MT/g tissue) in MT of the pancreas. The zinc in MT disappeared very rapidly when chicks which had been fed a diet containing high levels of zinc were fed a low zinc diet, indicating the extreme lability of this metal in this protein. The results suggest the involvement of MT in zinc homeostasis.

Pancreatitis in wild zinc-poisoned waterfowl

“…Zn concentrations were higher and more variable in the pancreas than in the liver of Zn-poisoned birds and, when dietary concentrations of Zn were reduced, Zn concentrations remained longer in the pancreas compared with other tissues examined (Williams et al, 1989). Tissue Zn concentrations in chickens drop rapidly after exposure returns to normal (Oh et al, 1979). The half-lives of Zn in metallothionein were estimated as 2.3 days in the pancreas, 1.5 days in the liver and 0.9 days in the kidney (Oh et al, 1979).…”

“…Zn is bound to metallothioneins found in the liver, kidney, intestinal mucosa and especially in the pancreas (Oh et al, 1979). Animals usually regulate Zn effectively, and consequently hepatic concentrations of Zn do not vary proportionately with dietary exposure.…”

Remedial investigation/feasibility study of the Clinch River/Poplar Creek Operable Unit. Volume 3. Risk assessment information. Appendixes E, F

“…All day-old chicks fed diets containing 16,000 mg zinckg feed for 5 weeks and 80% of those fed 8000 mgkg died, those on a 4,000 mg zinckg diet showed no significant reductions in growth or survival (Oh et al 1979). In a 60-day study, doses of 170 mgkg-day administered as zinc…”

“…Greater than 178 mgkg dry weight feed is considered excessive (Stahl et al 1989), and dietary concentrations >2000 mgkg dry weight feed are considered toxic (NAS 1979; Oh et al 1979;Stahl et al 1990). Turkey poults tolerated zinc levels up to 2000 ppm in starter diets for 21 days with no deleterious effects, but levels 24000 ppm resulted in marked growth depression (Vohra and Kratzer 1968).…”

Preliminary assessment of the ecological risks to wide-ranging wildlife species on the Oak Ridge Reservation

“…All day-old chicks fed diets containing 16,000 mg zinc/kg feed for 5 weeks and 80% of those fed 8000 mg/kg died; those on a 4000 mg zinc/kg diet showed no significant reductions in growth or survival (Oh et al, 1979). In a 6Oday study, doses of 170 mg/kg-day administered as zinc carbonate in the diet caused increased mortality and altered blood chemistry in mallards (Gasaway and Buss, 1972 Because mink are sensitive to PCB and Hg toxicity and inhabit wetland areas, they are potentially good indicators of environmental effects of these chemicals in aquatic habitats.…”