Transition from Normal to Hypersecretory Bronchial Mucus in a Canine Model of Bronchitis: Changes in Yield and Composition

Abstract

Density-gradient analysis was used to follow the transition from normal to hypersecretory bronchial mucus in a model of bronchitis induced in dogs by chronic exposure to SO₂ gas. Aspirates of saline bronchial lavage were obtained by fiberoptic bronchoscopy from dogs before, during a 6- to 9-month exposure period to SO₂ gas, and during a recovery period of similar duration. Prior to SO₂ exposure, aspirates from all animals had a low yield of nondialyzable macromolecules (15 ± 6 mg/aspirate) and similar composition. Specifically, epithelial glycoprotein of typical buoyant density was not detected; rather a glycoconjugate of higher buoyant density with features of both proteoglycan and glycoprotein was identified. Neutral lipids were predominant with lesser amounts of phospholipids; no glycolipids were detected. During the SO₂ exposure period, aspirates from five of the eight dogs contained components similar in buoyant density to human bronchitic glycoprotein. Glycoprotein isolated from the canine aspirates was similar to glycoprotein isolated from human chronic bronchitic sputum, having the same carbohydrate composition and range of oligosaccharide size. Further, during and after SO₂ exposure some aspirates contained appreciable amounts of glycolipids. These data demonstrate substantial similarities in composition between normal human and canine mucus and in mucus isolated from dogs with chronic airway inflammation induced by repeated irritant exposure and from human patients with chronic bronchitis.