Microwaves and heat in aldehyde fixation: model experiments with bovine serum albumin

Most model experiments concerning tissue fixation have used low concentrations of fixatives and proteins. Here, high concentrations (up to 32%) of bovine serum albumin (BSA) were reacted with formaldehyde (1-20%) and glutaraldehyde (0.5-4%). Gels were formed between 16% BSA and 10-20% formaldehyde at room temperature, but not with percentages of formaldehyde lower than 4%. Microwave application or heating in a water bath to 50 degrees C gave a gel from 1 to 20% formaldehyde. Sixteen percent BSA also gave a gel with glutaraldehyde from 0.5 to 4%. Cone and plate viscometry showed rapidly increasing viscosity at 4% formaldehyde and 16% BSA at room temperature. At 50 degrees C, gels formed at a low concentration of formaldehyde. Tissue fixation in which the local concentrations of protein may be in excess of 30% is probably more complete than in vitro experiments in which low concentrations of reagents have been used to permit subsequent spectrometry. This was confirmed by polyacrylamide gel electrophoresis of liver.