Hc. Kaulbach et al., ESTIMATION OF NASAL EPITHELIAL LINING FLUID USING UREA AS A MARKER, Journal of allergy and clinical immunology, 92(3), 1993, pp. 457-465
Background: The luminal surface of respiratory mucous membranes is lin
ed with an epithelial lining fluid (ELF) layer. Previous attempts to d
etermine ELF volumes in airways have used dyes or freely diffusible mo
lecules such as urea, yet have not led to a universally accepted metho
d. The nasal mucous membrane provides an accessible area to examine wh
ether urea is an appropriate marker of respiratory ELF volume. Methods
and Results: Collection of undiluted nasal secretions after either gl
andular stimulation or induction of vascular permeability confirmed th
at plasma urea and nasal urea concentrations are equivalent. Baseline
ELF volume was calculated as 800 mul/nostril. The calculated molar con
centrations of urea in ELF did not vary with either methacholine or hi
stamine challenge. Conclusions: These data indicate the plasma, inters
titial, glandular and ELF urea concentrations are equivalent and, ther
efore, that urea is a useful marker of ELF volume in the nasal mucosa.