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Article

Metallothionein-Null Mice Absorb Less Zn from an Egg-White Diet, but a Similar Amount from Solutions, although with Altered Intertissue Zn Distribution

Division of Clinical Biochemistry, Institute of Medical and Veterinary Science, Adelaide, SA 5000 Australia

The influence of metallothionein (MT) on Zn transfer into non-gut tissues was investigated in MT-null (MT-/-) and normal (MT+/+) mice 4 h after oral gavage of aqueous ⁶⁵ZnSO₄solution at doses of 154, 385, 770 and 1540 nmol Zn per mouse. Zn transfer was not significantly different between MT+/+ and MT-/- mice and was directly proportional to the oral dose (slope = 0.127, r = 0.991; 0.146, r = 0.994, respectively). Blood ⁶⁵Zn and plasma Zn concentrations increased progressively in MT-/- mice at doses >154 nmol Zn, reaching levels of 2.4% of oral dose and 60 µmol/L, respectively, at the 1540 nmol Zn dose. The corresponding values for MT+/+ mice were approximately half, 1.0% and 29 µmol/L. Intergenotypic differences were found in tissue distribution of ⁶⁵Zn within the body; MT-/- mice had higher ⁶⁵Zn levels in muscle, skin, heart and brain, whereas MT+/+ mice retained progressively more Zn in the liver, in conjunction with a linear increase in hepatic MT up to the highest Zn dose. MT induction in the small intestine reached its maximum at an oral dose of 385 nmol Zn and did not differ at higher doses. Absorption of a 770 nmol ⁶⁵Zn dose from a solid egg-white diet was only one fourth (MT+/+) and one eighth (MT-/-) of the Zn absorption from the same dose of ⁶⁵Zn in aqueous solution. MT+/+ mice had greater (P < 0.05) Zn absorption from the egg-white diet than did MT-/- mice, indicating that gut MT confers an absorptive advantage, but only when Zn is incorporated into solid food.

KEY WORDS: • zinc • metallothionein • intestinal absorption • metallothionein-null mice

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