Metallothionein mRNA induction in mouse small bowel by oral cadmium and zinc

Induction of metallothionein mRNA was investigated in organs of mice receiving oral zinc and cadmium. The low molecular weight, heat stability, and 30% cysteine content of metallothionein facilitated its detection in cell-free translation products analyzed by Sephadex G-50 chromatography and by gel electrophoresis. Native and heat-denatured [35S]cysteine-labeled polypeptides directed by poly(A)+ mRNA from organs of mice exposed orally to 3 mg CdCl2 or 15 mg ZnCl2 were compared with those of control mice. Although parenteral administration of CdCl2 (30 micrograms) did not elicit a measurable metallothionein mRNA accumulation in gut, oral administration of this metal induced intestinal metallothionein mRNA to high levels; translatable metallothionein mRNA was not detected in control organs. Five hours after oral CD or Zn, metallothionein constituted 12-17% of [35S]cysteine directed into protein by gut mRNA, and metallothionein mRNA was induced to similar levels in liver, kidney, and spleen of the same mice. After oral Zn, metallothionein mRNA levels in proximal jejunum were twice those in other regions of intestine. Metallothionein mRNA accumulates rapidly in small bowel after oral Zn and Cd; simultaneous induction in other mouse organs indicates a systemic response.