The effects of mercaptoethanol-formaldehyde on tissue fixation and protein retention
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Abstract
The study compared the effects of mercaptoethanol-formaldehyde and formaldehyde alone, on tissue fixation and protein
retention in human and mouse tissues. Shrinkage of tissues and the penetration rate of the fixatives were assessed. The
cross-linking ability of the fixatives was determined by viscometry, sodium dodecyl sulphate-polyacrylamide gel electrophoresis, and spectrophotometry, using bovine serum albumin and human haemoglobin. Tissues fixed in buffered 0.0025%
mercaptoethanol-4% formaldehyde showed good nuclear and cytoplasmic detail, better than those fixed in buffered 4%
formaldehyde. There was no significant difference in shrinkage. A mixture of 0.0025% mercaptoethanol-4% formaldehyde
penetrated faster into adult liver than 4% formaldehyde. The mean penetration rate (_+SE) or coefficient of diffusibility of 0.0025%
mercaptoethanol-4% formaldehyde into adult liver was 1.32 _+ 0.01 and that of 4% formaldehyde was 1.12 _+ 0.06 (p<0.04). Both
fixatives diffused more rapidly into mouse liver than into human liver. The cross-linking ability of mercaptoethanol-formaldehyde depends on the concentration of the fixative and the time of fixation. Bovine serum albumin (15%) and 0.1% mercaptoethanol alone formed a gel, whilst electrophoresis showed monomers in the supernatant. Mercaptoethanol (0.1%) also rapidly
decreased the absorption at 420 nm, suggesting denaturation. It seems that mercaptoethanol increases the number of thiol
groups available to form cross-links with formaldehyde. This study demonstrated that mercaptoethanol-formaldehyde fixed
and cross-linked tissues better than formaldehyde at 3 h and 4 h, but not at 1 h and 2 h. The most effective concentration of
mercaptoethanol for tissue fixation in 4% formaldehyde is 0.0025%