ENDOGENOUS ENZYMES CAUSE STRUCTURAL AND CHEMICAL ARTIFACTS IN METHACRYLATE-EMBEDDED AND CELLOIDIN-EMBEDDED SECTIONS OF UNFIXED FREEZE-DRIEDTISSUES

Bovine exocrine pancreas and fish (Rivulus ocellatus marmoratus) liver containing pancreatic acini were cryofixed, freeze-dried, and embedde d in methacrylate or double-embedded in colloidin and paraffin. In che mically unfixed sections incubated in aqueous solutions, dissolution o f zymogen granules was coincident with loss of tissue structure and an tigenicity. Type II-S soybean protease inhibitor at 150 mg/litter duri ng section flotation and in aqueous reagents used for immunohistochemi stry prevented these artifacts and allowed the use of more dilute anti body solutions. Loss of glycogen from fish hepatocytes was most rapid in areas adjacent to pancreatic acini. Rapid loss of glycogen was attr ibuted to amylase and was prevented by using poly-L-lysine instead of 3-aminopropyltriethoxysilane slide adhesive and by using alcoholic sol utions during PAS staining. Inhibition of endogenous enzymes is an imp ortant consideration in the development of histological protocols with freeze-dried tissue sections.