DISTRIBUTION OF SUBSTANCE-P AND CALCITONIN-GENE-RELATED PEPTIDE-IMMUNOREACTIVE NERVE-FIBERS IN THE TRACHEA OF CHRONICALLY HYPOXIC RATS

The distribution of substance P and calcitonin gene-related peptide im munoreactive nerve fibers in the trachea was compared between normoxic and chronically hypoxic rats (at 380 mm Hg for 10 weeks). In the norm oxic trachea, the immunoreactivity to either peptide was seen in the n erve fibers in four principal locations: a) within and b) under the ci liated epithelium, c) within the smooth muscle bundles in the posterio r wall, and d) in the connective tissue and around blood vessels in th e lamina propria and submucosa. These immunoreactive fibers within the epithelium and smooth muscle bundles, in the connective tissue, and a round blood vessels were thin and displayed some varicosities, and tho se under the epithelium appeared as thick nerve bundles. When the dist ribution and density of immunoreactive fibers were compared between no rmoxic and chronically hypoxic tracheas, there was a difference in num ber of substance P and calcitonin gene-related peptide immunoreactive fibers penetrating into the epithelium, although there was no differen ce in the other three locations. The mean number of substance P and ca lcitonin gene-related peptide immunoreactive intraepithelial fibers pe r section of the chronically hypoxic trachea was significantly increas ed, Because substance P and calcitonin gene-related peptide are predom inant signal peptides of primary sensory neurons, the increase of subs tance P and calcitonin gene-related peptide immunoreactive fibers sugg ests that altered airway reflexes may be a feature of hypoxic adaptati on.