Preliminary oxidation in histochemical staining methods for cholesterol.

The need for preliminary oxidation with histochemical methods for cholesterol was investigated on silica-coated sheets and in tissue sections. The techniques used were the Schultz reaction, perchloric acid-naphthoquinone (PAN), Lewis & Lobban's ferric alum-sulphuric acid reagent and Okamoto's iodine-sulphuric acid. The oxidants assessed were ferric chloride, ferric alum, potassium permanganate, ammonium sulphamate and ultraviolet light. The best combinations amongst those tested in order of reactivity were FeCl3-PAN, ferric alum-Schultz, Lewis-Lobban (no additional oxidant), iodine-sulphuric acid (no additional oxidant). Authentic preparations of cholesterol oxidation products were stained with these methods, but the nature of the oxidized product in the preliminary stage could not be determined.