Tracheobronchial secretions collected from intact dogs. I. Protein and mucous glycoprotein composition

Tracheobronchial secretions (TBS) were collected in situ from intact, anesthetized dogs, and the protein composition and distribution were studied. TBS were separated into supernatant and pellet phases by centrifugation. The supernatant phase comprised 85%, by weight, of the secretory mixture; yet it contained only 58% of the total protein. Peptides of apparent molecular weights ranging from 16,000 to 154,000 daltons were present in the supernatant phase. Electrophoretic and immunochemical comparisons with canine serum suggested that certain of the peptides were of plasma origin including albumin, IgG, IgA, and IgM. Albumin and IgG comprised approximately 70% of the supernatant phase protein. Three percent of the total TBS protein was contributed by the peptide portion of mucous glycoproteins (mucins), and 97% of the mucin protein separated into the pellet phase. When compared to mucus collected from a canine tracheal pouch, TBS was less concentrated in mucins, and differences were observed in electrophoretic profiles between the two samples.