Metallothionein-null mice absorb less Zn from an egg-white diet, but a similar amount from solutions, although with altered intertissue Zn distribution

The influence of metallothionein (MT) on Zn transfer into non-gut tissues w as investigated in MT-null (MT-/-) and normal (MT+/+) mice 4 h after oral g avage of aqueous (ZnSO4)-Zn-65 solution 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 Zn-65 and plasma Zn concentrations increased progressively in MT-/- mice at doses > 154 nmol Zn , reaching levels of 2.4% of oral dose and 60 mu mol/L, respectively, at th e 1540 nmol Zn dose. The corresponding values for MT+/+ mice were approxima tely half, 1.0% and 29 mu mol/L. Intergenotypic differences were found in t issue distribution of Zn-65 within the body; MT-/- mice had higher Zn-65 le vels in muscle, skin, heart and brain, whereas MT+/+ mice retained progress ively more Zn in the liver, in conjunction with a linear increase in hepati c 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 do ses. Absorption of a 770 nmol Zn-65 dose from a solid egg-white diet was on ly one fourth (MT+/+) and one eighth (MT-/-) of the Zn absorption from the same dose of Zn-65 in aqueous solution. MT+/+ mice had greater (P < 0.05) Z n absorption from the egg-white diet than did MT-/- mice, indicating that g ut MT confers an absorptive advantage, but only when Zn is incorporated int o solid food.