Estimation of nasal epithelial lining fluid using urea as a marker

Area of Science:

• Respiratory physiology
• Biomarker research

Background:

• The epithelial lining fluid (ELF) layer coats respiratory mucous membranes.
• Previous methods for determining ELF volume, such as dyes or urea, lacked universal acceptance.

Purpose of the Study:

• To evaluate urea as an appropriate marker for respiratory epithelial lining fluid (ELF) volume.
• To assess ELF volume in the accessible nasal mucous membrane.

Main Methods:

• Collected undiluted nasal secretions after glandular stimulation or vascular permeability induction.
• Measured plasma and nasal urea concentrations.
• Calculated baseline ELF volume and urea concentrations in ELF.

Main Results:

• Plasma and nasal urea concentrations were found to be equivalent.
• Baseline epithelial lining fluid (ELF) volume was determined to be 800 microliters/nostril.
• Urea concentrations in ELF remained consistent despite methacholine or histamine challenges.

Conclusions:

• Plasma, interstitial, glandular, and ELF urea concentrations are equivalent.
• Urea is confirmed as a useful and validated marker for assessing ELF volume in the nasal mucosa.