Autoradiographic demonstration of cadmium not bound to metallothionein using 14C-labeled thiazolylazo-naphthol.

We describe a new autoradiographic technique for differentially demonstrating the presence of trace amounts of cadmium that remains unbound to metallothionein in tissue sections. This procedure involves [14C-1,4,5,8-naphthol]-1-(2-thiazolylazo)-2-naphthol (TAN) instead of a metal radioisotope. Tissue sections were stained using labeled TAN, and were then subjected to routine autoradiographic procedures. The results obtained indicated that the distribution of photographic grains truly reflected the distribution of metallothionein-unbound Cd in the sections. This demonstrates the suitability of this procedure for the differential demonstration of cadmium present in different chemical forms in tissues.