Mucus protection and airway peroxidation following nitrogen dioxide exposure in the rat

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Abstract
In the current study, biochemical measures of lipid peroxidation following 4‐h inhalation exposure to 76 mg/m 3 (40 ppm) nitrogen dioxide were correlated with measures of deposition and tissue antioxidant levels in the nasal cavity and the trachea of the Fischer rat. In addition, respiratory‐tract mucus samples were collected via esopha‐geal cannulation and nasopharyngeal lavage over known time periods, and were analyzed for phospholipid (PL) content to provide an index of the unsaturated lipids (UL) that they may contain. UL are thought to be important in the scavenging of oxidants by the mucous lining layer. Nasal deposition efficiency, as measured in the surgically isolated upper respiratory tract under unidirectional flow conditions, averaged 25%, corresponding to an absolute deposition rate of 41 nmol/min. Vitamin E levels averaged 1.7, 5.9, and 0.7 nmol/μmol PL in nasal, tracheal, and pulmonary tissues, respectively. The level in the trachea was significantly (p < 0.005) higher than in the other tissues. As estimated from the increase in lavage PL content over 1 h, the overall mucous PL transport rate was less than 0.013 nmol/min, suggesting the PL of the mucous lining layer could not offer significant protection against the inhaled NO 2 . Conjugated dienes were detected in two of four pooled nasal tissue samples. Thio‐barbituric acid‐reactive material levels in tracheal tissues were significantly elevated over control levels by NO 2 (p < 0.05). Thus, despite the relatively high vitamin E levels, 4‐h NO 2 exposure appeared to result in lipid peroxidation in the trachea and, perhaps, in the nasal airways of the rat, a result that correlated with the apparent lack of oxidant‐scavenging species in the mucus lining these airways.