LECTIN-DETECTABLE GLYCOCONJUGATE PROFILE OF THE TRACHEAL SECRETIONS AND EPITHELIAL GLYCOCALYX IN SHEEP - EFFECT OF MUSCARINIC STIMULATION

Reflex mucus secretion in the airways serves a defense function that i ncludes the binding of bacteria to mucus glycoconjugates thereby preve nting bacterial adherence to the epithelium. We therefore compared the lectin-detectable glycoconjugate profile of the epithelial glycocalyx and luminal secretions under baseline conditions and after muscarinic receptor stimulation in the sheep trachea. The sheep were intubated w ith a double-balloon nasotracheal tube to create a tracheal chamber fo r collection of secretions. After an initial lavage of the chamber to clear it of secretions, the sheep received an intravenous injection of normal saline, 0.5 mg/kg pilocarpine, or 0.5 mg/kg pilocarpine after pretreatment with 0.2 mg/kg atropine. Tracheal lavage was repeated 2 h later, and the sheep were then killed. An enzyme-linked lectin assay and lectin histochemistry were used to characterize glycoconjugate res idues in tracheal secretions and in the apical epithelial glycocalyx, respectively. Eight different lectins were used to detect N-acetyl gal actosamine, alpha-galactose, alpha-galactose-N-acetyl galactosamine, b eta-galactose, beta-galactose-N-acetyl galactosamine, alpha-fucose, al pha-glucose, alpha-mannose and alpha-(2-3)sialyl residues. After norma l saline, reactivity was present for all glycoconjugates in secretions and in the glycocalyx. After pilocarpine, there was a greater reactiv ity for alpha-galactose, alpha-galactose-N-acetyl galactosamine, alpha -mannose, alpha-(1-3)mannose, alpha-fucose, sialyl residues, and possi bly alpha-glucose by 200 to 692% (n = 6, p < 0.05) and similar reactiv ity for beta-galactose and beta-galactose-N-acetyl galactosamine in se cretions; in the glycocalyx, there was greater reactivity for beta-gal actose, beta-galactose-N-acetyl galactosamine, alpha-(1-3)mannose, and sialyl by 209 to 700% (p < 0.05), but there were only minimal differe nces in the other glycoconjugates. Atropine prevented all effects of p ilocarpine. These observations suggest that the secretions and the epi thelial glycocalyx in sheep trachea have different glycoconjugate prof iles. Muscarinic stimulation leads to profound but different alteratio ns in both glycoconjugate profiles, which could influence the competin g binding of the secretions and epithelium to bacteria colonizing the airway.