Changes in the distribution of the substance P and calcitonin gene-relatedpeptide immunoreactive nerve fibers in the laryngeal mucosa of chronicallyhypoxic rats

The distribution and abundance of substance P (SP) and calcitonin gene-rela ted peptide (CGRP) immunoreactive nerve fibers in four different regions of the laryngeal mucosa were compared between normoxic and chronically hypoxi c rats (10% O-2 and 3.0-4.0% CO2 for 3 months). In the chronically hypoxic laryngeal mucosa, the number of SP and CGRP fibers within and just beneath the epithelium, and around the laryngeal gland was increased in comparison with those in the normoxic controls. Especially in the epiglottic and aryte noid regions, the number of intraepithelial SP fibers was increased remarka bly. Most intraepithelial SP and CGRP fibers penetrated into the epithelium to extend to the luminal surface. There was no distinct difference in the distribution and abundance of these peptidergic fibers in the mucosa of the normoxic and chronically hypoxic vocal cord regions. These results suggest that the increased density of SP and CGRP fibers within the epithelium of the upper laryngeal mucosa is a predominant feature of hypoxic adaptation, and this may be involved in airway protection, swallowing, and other functi ons in the chronically hypoxic environment. In addition, the increased SP a nd CGRP fibers around the laryngeal gland suggest an enhanced mucous secret ion, and this may participate in the airway defense mechanism in low O-2 co nditions.