Effects of vaccination with Haemophilus influenzae on adrenoceptor function of tracheal and parenchymal strips

Haemophilus influenzae is a bacterium that can be isolated from the deeper airways of asthmatic patients. We investigated the effect of vaccination with H. influenzae on alpha and beta adrenoceptor function in guinea-pig tracheal spirals and lung parenchymal strips. The tracheal spirals from H. influenzae-vaccinated animals showed significantly less relaxation to isoproterenol as compared to controls, independent of whether the trachea was maximally contracted with carbachol or only exhibited an intrinsic tone. Furthermore, an increased contractile response to carbachol was observed in these spirals. To isoproterenol in the presence of a beta-2 adrenergic antagonist (H35/25), or to salbutamol alone, the tracheal preparations from H. influenzae-vaccinated animals also showed a decreased relaxation. These results suggest involvement of both beta-1 and beta-2 subtype adrenoceptors. On the other hand, lung parenchymal strips from vaccinated guinea-pigs relaxed significntly more to these drugs. This effect was not influenced by H35/25 but could be inhibited by phenoxybenzamine. Histamine-induced contraction did not differ between the groups. These results indicated that H. influenzae causes a partial blockade of the beta adrenoceptors in tracheal spirals and, therefore, may have important implications in asthmatic bronchitis. In contrast, parenchymal lung strips of the H. influenzae-pretreated group showed an increased relaxation.