Which compound is described as highly lipid sensitive but not permanent in tissue sections?

• A. 3,4-Benzpyrene
• B. Oil Red O
• C. Nile Blue Sulfate
• D. OTAN

Answer: (A)

The idea here is that certain stains are lipid-soluble and will only clearly mark fats if the lipids are preserved in the tissue. However, during routine tissue processing, fats are dissolved away by organic solvents used for dehydration and clearing, so the stain doesn’t stay in the section. Oil Red O is the classic example of this behavior: it binds to neutral lipids and is used on fresh-frozen sections (or in lipid-preserving protocols), but once the tissue is processed for paraffin embedding, the lipids are removed and the stain is not permanent. That’s why it’s described as highly lipid sensitive but not permanent in tissue sections.

The other choices don’t fit this description because they aren’t lipid-specific stains with this processing sensitivity: 3,4-Benzpyrene is a lipophilic compound but not a histologic lipid stain; Nile Blue Sulfate serves different staining purposes, and OTAN is not a standard lipid-staining agent.