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I I I I I I I I I I I I I I I I ass AUTHOR: KING, MALCOM, ANNE WIGHT, GEORGE T. SesANCTIS, JUDY EL-AZAB, DAVID M. PHILLIPS, G.ELSPETH ANGUS AND MANUEL G. COSIO DATE: 1989 TITLE: MUCUS ITYPERSECRETION AND VISCOELASTICITY CHANGES IN CIGARETTE- SMOKING DOGS 9ITATION: EXPERIMENTAL LUNG RESEARCH 15:375-389 (1989) STUDY DESIGN: 9 Male beagle dogs, previously tracheostomized were trained to stand quietly in a harness, and smoke was delivered via a cuffed tracheostomy tube. A 35-cm3 bolus of smoke was introduced into the inspiratory line each 20 s, using unfiltered 70-mm cigarettes (20 mg tar, 1.2 mg nicotine, and 15.8 mg CO per cigarette). Each dog smoked 10 cigarettes per day over 2.5 h, 5 days per week. Two dogs were exposed for 6 months, 7 dogs were exposed for 10 month. Five dogs served as sham-smoking controls. Mucus was collected twice weekly without drugs from the lower trachea for 2-5 minutes. The rheologlcal properties of the mucus samples were determined by magnetic rheometry, which yields elastlcity and viscosity as a function of frequency. The mucus was weighed and the galactose content determined. The mucus collection rate served as an index of tracheal mucus flux, and the galactose assay as a marker of mucous glycoprotein content. The tracheal mucus linear velocity (TMV) was determined periodically by observing charcoal particle transport bronchoscopically. FINDINGSlRESULTS: Eight of 9 smoking dogs developed mucus hypersecretion (flux >2 x control) versus I of 5 controls (pa0,01). Tracheal mucus linear velocity did rot change significantly in 10 month exposure. In the first 2-4 months of smoking, the elasticity and viscosity of the mucus both decreased (mean at 4 months = 42% of control, p<0.01), as did the galactose content (mean at 4 months = 48% of control, p<0.01). After 6 months, the viscoelasticity returned toward the initial control level, while the galactose content remained low, suggesting an alteration in the nature of the mucous glycoprotein. CONCLUSIONS: This study showed that chronic mucus hypersecreation can be developed in dogs with 6-10 months of exposure to whole cigarette smoke via a tracheostomy. The hypersecretion is highly variable but relatively stable, lasting for at least 2 months. Regardless of the degree of hypersecretion reached with smoke exposure, both the time course and the magnitude of the alteration in the viscoelastic properties of the mucus were very similar between dogs. This was evidenced by a decrease in the mechanical impedance early in the smoke exposure period, followed by a return to the initial control level despite continued sxposure._Tracheal mucus linear velocity did not change significantly in 10 month exposure, this is consistent with a number of factors associated with the study, including the favorable alteration in mucus rheology, implying that the cilia, although more loaded, were presented with mucus that was more easily cleared. The authors state, that the way in which the dogs responded to the insult by alterations in both quantity and quality of mucus might be interpreted as evidence for a protective mechanism preventing major damage to the airway epithelium or the parenchyma. 0 m u n ~ p ~. w W I