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

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Abstract
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.