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Sumatriptan (Imigran) is a potent and highly selective 5-HT1 receptor agonist often used in treating acute migraine. Intranasal sumatriptan is well absorbed and is generally effective in relieving headache. However, the effects of Imigran given intratracheally have rarely been well explored. We aimed to verify the effect of Imigran, which acts on the tracheal smooth muscle directly in vitro. We examined the effectiveness of Imigran on isolated rat tracheal smooth muscle by testing: (1) effect on tracheal smooth muscle resting tension; (2) effect on contraction caused by 10(-6) M methacholine as a parasympathetic mimetic; (3) effect of the drugs on electrically induced tracheal smooth muscle contractions. The results indicated that the addition of methacholine to the incubation medium caused the trachea to contract in a dose-dependent manner. The addition of Imigran at doses of 10(-5) M or above elicited a significant relaxation response to 10(-6) M methacholine-induced contraction. Imigran could inhibit electrical field stimulation-induced spike contraction. It also had a minimal effect on the basal tension of trachea as the concentration increased. The study indicated high concentrations of Imigran could cause bronchodilation to reduce asthma attacks not only by blocking parasympathetic tone, but also by directly antagonizing the effect of cholinergic receptors.