Abstract
Recent studies have implicated a role for tumour necrosis factor-alpha (TNFalpha) in the development of the asthmatic reaction. In this study, we examined the influence of TNFalpha on isotonic contraction of tracheal smooth muscle of the guinea-pig in vitro in response to methacholine. Tracheal rings were incubated with recombinant human (rh)TNFalpha (3x10(-11) M) for 30 min, and concentration-response curves to methacholine before and after incubation with rhTNFalpha were compared with the control. The present study demonstrates that rhTNFalpha increases maximal isotonic contraction of tracheal smooth muscle to methacholine (mean+/-SEM 169.6+/-43%, p<0.005). This effect was observed only after a 30 min delay between incubation and methacholine challenge testing. Experiments with 10(-13) - 10(-10) M rhTNF-alpha yielded similar results at all concentrations used. The effects of rhTNFalpha (10(-11) M) on tracheal hyperreactivity could be completely inhibited by coincubation with dimeric rTNF-receptor-p80 construct (10(-10) M) (p<0.01). In order to analyse secondary mediator release, experiments using coincubation with indomethacin (10(-5) M) and WEB 2086 (10(-6) M), a specific platelet activating factor (PAF) antagonist, demonstrated that the effect of rhTNFalpha on tracheal rings was mediated by PAF, since WEB 2086 completely inhibited rhTNFalpha-induced hyperreactivity (p<0.05). In conclusion, this study demonstrates that recombinant human tumour necrosis factor-alpha induces hyperreactivity in tracheal smooth muscle in vitro, which was shown to be mediated by platelet activating factor. Our study emphasizes the role of tumour necrosis factor-alpha in the pathophysiology of bronchial hyperresponsiveness.
