Regional distribution of metallothionein and zinc in the mouse gut: comparison with metallothionien-null mice.

Gut Zn homeostatic responses to low, replete, and excess dietary Zn (10, 150, and 400 mg Zn/kg, respectively) were compared in mice with (MT+/+) and without (MT-/-) metallothionein (MT) expression. MT concentrations decreased progressively from stomach (12.9 nmol Cd bound/g) to colon (4.6 nmol Cd bound/g). Small intestinal MT was increased in mice fed the 400-mg Zn/kg diet (+130%, duodenum; +56%, jejunum; +29%, terminal ileum), but not in the stomach, cecum and colon. Zn concentrations were much higher in the distal gut at increasing Zn intakes in MT+/+ mice but to a lesser extent in MT-/- mice. On the 10-mg Zn/kg diet, MT-/- mice had 45% more Zn in the jejunum/ileum than MT+/+ mice. In fasted (20 h) mice, Zn concentrations in all gut regions were similar to those of MT+/+ mice fed the 10-mg Zn/kg diet, irrespective of prior Zn intake or genotype. Liver MT quadrupled in mice fasted after the 10-mg Zn/kg diet but only doubled after the 400-mg Zn/kg diet, a trend also present in gut MT. Glucagon administration stimulated gut as well as liver MT, implicating it as a major component of the MT response to fasting. MT-/- mice had five times more variation than MT+/+ mice in plasma Zn over all dietary groups. Together, these findings demonstrate that without MT, there is little modification of regional gut Zn concentrations in response to extremes of dietary Zn and poorer regulation of Zn homeostasis.