Differential pulse polarographic determination of murine metallothionein induction kinetics

Quantitative determination of tissue levels of metallothionein was performed using differential pulse polarographic analysis. Cadmium induction of mouse hepatic metallothionein was observed to be linear with respect to dose until a sharp saturation maximum was reached. This metal-stimulated synthesis was completely inhibited by actinomycin D. It was found that a 2- and 7-fold molar excess of copper and zinc, respectively, was necessary to induce hepatic metallothionein synthesis equivalent to a single dose of cadmium. Although liver was the most dynamic tissue in terms of synthetic production, the intestine had the highest basal level. However, induction in the latter tissue was greatly decreased relative to liver or kidney, with no measurable synthesis after a single metal dose. Induction kinetics was similar for all inducing metals with the exception of cadmium-induced hepatic protein, which remained unchanged for 2 weeks and decayed with an apparent t 1/2 of 32 days. Furthermore, with the exception of intravenous zinc dosing, which elicited no hepatic biosynthesis, initial induction kinetics was invariant with administration route. It was observed that chronic subcutaneous administration of sufficient cadmium to saturate hepatic metallothionein synthesis resulted in a coincident onset of toxic symptoms.