Cigarette smoke‐induced changes in guinea‐pig airway responsiveness to histamine and citric acid

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Abstract
The effect of 50 min cigarette smoke exposure on airway responsiveness to the bronchoconstrictor and tussive effects of histamine and citric acid has been examined in guinea-pigs. Intravenous histamine increased intratracheal pressure (ITP) in anaesthetized guinea-pigs and the dose-response curve was significantly (P less than 0.05) steeper in cigarette smoke- than in air-exposed animals. ED50 values were 11.4 nmol kg-1 (7.4-16.8, 95% confidence interval) and 42.5 nmol kg-1 (28.8-61.4, 95% confidence interval), respectively (P less than 0.05) in smoke- and air-exposed guinea-pigs indicating an enhanced reactivity. However, the sensitivity to intravenous histamine was not changed by the cigarette smoke exposure, and the maximum increase in intratracheal pressure was the same as in control animals (air: 247 +/- 21%, n = 4; smoke: 223 +/- 18%, n = 7). The cigarette smoke-induced hyperresponsiveness to intravenous histamine was not altered by pretreatment with nebulized lidocaine (0.20 M), ipratropium bromide (0.30 mM) or cromoglycate (0.06 M), suggesting that a neural reflex is unlikely to be involved in the development of hyperresponsiveness. Conscious, smoke-exposed guinea-pigs had a significantly (P less than 0.001) reduced responsiveness to citric acid (0.40 M) and cigarette smoke. Both cough and bronchoconstriction were suppressed for about 1 h, but unchanged 24 h after exposure. The hyporesponsiveness to citric acid was inhibited by atropine (1.4 mumol kg-1 i.p.) and may therefore, at least in part, be due to increased airway secretions. The present data demonstrate that inhalation of cigarette smoke may alter guinea-pig airway responsiveness to tussive and bronchoconstrictor stimuli.(ABSTRACT TRUNCATED AT 250 WORDS)