Dimedone as an Aldehyde Blocking Reagent to Facilitate the Histochemical Demonstration of Glycogen

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Abstract
The demonstration of glycogen by the periodic acid-Schiff technique can be clarified by the interposition of a short dimedone blockade after the periodic acid oxidation. This blocks the PAS reaction of the vast majority of materials, but a very much longer blockade is required to abolish the reaction of glycogen. The dimedone-PAS method is valuable in situations where the demonstration of glycogen is otherwise difficult because of the proximity of diastase-fast PAS positive materials. For this purpose dimedone is best used in alcoholic solution (5% in absolute alcohol for about 3 hr at 60°C), since an aqueous solution permits diffusion of the aldehydes produced from the oxidation of glycogen. A saturated aqueous solution, or a 5% solution in 80% alcohol, is much more rapid in its blocking action, however, and may be more satisfactory when dimedone is used simply as an aldehyde blocking reagent.

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