Comparison of methods of metallothionein quantification: cadmium radioassay, mercury radioassay, and radioimmunoassay.

A comparison of the Hg radioassay (i.e. "Piotrowski" assay), the Cd radioassay (i.e. "cadmium-hemolysate" assay), and the radioimmunoassay (RIA) for metallothionein (MT) was performed for livers from control, Cd-, and Zn-pretreated rats. Results indicate that the Cd and Hg radioassays gave similar results in all cases. The RIA values compared very favorably to those obtained by the metal saturation assays for livers from control rats. The values obtained for livers from Cd- or Zn-treated animals were generally lower in the RIA than in the Hg or Cd radioassay, ranging from 36 to 75% of the metal saturation assays. The source of this discrepancy cannot be discerned from the present data. However, the various assay systems employed did yield MT concentrations that followed similar intraassay patterns, being lowest in control, elevated to an intermediate level with Cd treatment, and highest following Zn treatment.