Determination of metallothionein in tissues by radioimmunoassay and by cadmium saturation method

The diversity of reported basal metallothionein (MT) values in animal tissues has made it necessary that the presently available methods be further developed and compared for their accuracy, reproducibility, sensitivity, and specificity. A radioimmunoassay (RIA) to quantitate MT in animal tissues was developed and its performance compared to that of a cadmium saturation method. The procedure is more accurate and reliable but no more time-consuming than other techniques in current use. It offers the advantages of greater specificity and sensitivity thus enabling the determination of basal levels of MT in tissues and the analysis of small samples, for example, biopsies, cultured cells, in vitro protein synthesis, etc. The use of a polyclonal antiserum is advantageous in that total MT can be determined in any tissue from a variety of animal species. Both nonspecific and specific interference in the assay can be eliminated by heat treatment of the sample followed by a short preincubation with cadmium. The sensitivity of the RIA is 10 ng MT/g tissue. The cadmium saturation assay is unsuitable for the measurement of low levels of MT due to its nonspecific nature and its detection limit (10 micrograms MT/g tissue) but it is useful where large amounts of the protein are present in a tissue. Difficulties arising in the analysis of MT by both methods are discussed and solutions are offered. The basal levels of MT in the brain, kidney, liver, lung, muscle, pancreas, small intestine, and spleen of rats are determined by RIA and are shown to be generally lower than the currently accepted values measured by other techniques.