The effect of inhaled 5-hydroxytryptamine (5-HT, serotonin) on airway calibre in man.

Since platelet activation has been incriminated in the pathogenesis of asthma, we have investigated the effect of one of its major granule-derived mediators, 5-hydroxytryptamine (5-HT, serotonin) on airway calibre in normal (12), atopic non-asthmatic (12) and atopic asthmatic subjects (16). On separate days subjects inhaled increasing concentrations of 5-HT and methacholine, and airway response was measured as FEV1, Vmax30 and sGaw. All subjects bronchoconstricted with methacholine, geometric mean provocation concentrations causing a 20% fall in FEV1 (PCf20) for the normal, atopic non-asthmatic and atopic asthmatic subjects being 28.6, 18.3 and 0.71 mM respectively. In contrast, 5-HT up to a maximum concentration of 77 mM had no consistent effect on FEV1, Vmax30 or sGaw in any of the subject groups. Thus, in contrast to a variety of animals, 5-HT is unlikely to serve as a significant bronchoconstrictor mediator in man.