Abstract
Exposure of tissue sections to the original Unna ferric ferricyanide reagent for 10 min produces strong blue staining of elastica, demonstrating a reducing activity of this substance. This activity was analyzed histochemically in sections of human skin, kidney and spleen by observing its resistance to various blocking techniques, correlated with the results of corresponding end group methods. For comparative purposes the properties of four other reducing components (keratin, melanin, fibrin and proximal tubule cytoplasm) were studied. The results indicate that the reducing activity of the elastica is largely a function of phenolic groups, presumably in the tyrosine residues of elastin. In view of the inordinate resistance of this activity to preliminary treatment with aqueous periodic acid, the presence of additional minor reducing components, such as lipochrome or polytyrosines, cannot be excluded. This distinctive histochemical property should prove useful in studies of pathologically altered elastica and other "elastotic" material.