Glycogen fixed in which fixative is more resistant to diastase digestion than with other fixatives?

• A. Methanol
• B. Picric acid
• C. Formalin
• D. Glutaraldehyde

Answer: (B)

Glycogen’s behavior in PAS staining after enzyme digestion depends on how the tissue is fixed. Diastase removes glycogen, so in PAS-D stains you’re looking to see how much glycogen remains after digestion. Some fixatives alter glycogen’s accessibility to the enzyme. Picric acid fixation tends to preserve glycogen in a way that makes it less accessible to diastase, so glycogen remains PAS-positive after digestion to a greater extent than with other fixatives. This makes glycogen fixed in picric acid more resistant to diastase digestion. In contrast, methanol, formalin, or glutaraldehyde do not confer the same level of resistance, so diastase more readily removes the glycogen in those tissues.