Increased airway reactivity in the guinea‐pig follows exposure to intravenous isoprenaline.

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Abstract
1. Intravenous infusion of (+/‐) isoprenaline (1‐100 micrograms kg‐1 h‐1) enhanced airway responses (resistance, RL; and compliance, Cdyn) to histamine (1.0‐1.8 micrograms kg‐1) and bombesin (100‐240 ng kg‐1), whereas airway responses to vagal stimulation remained unchanged. 2. Bilateral vagotomy before intravenous infusion of (+/‐)isoprenaline (100 micrograms kg‐1 h‐1) prevented development of airway hyperreactivity to histamine or bombesin, yet vagotomy after infusion of isoprenaline was without effect. 3. Prior treatment with atropine (1 mg kg‐1) did not influence the capacity of (+/‐)isoprenaline (100 micrograms kg‐1 h‐1) to increase airway reactivity to bombesin. 4. Despite a 500‐fold difference in spasmolytic potency in vivo, infusion of (+)isoprenaline (100 micrograms kg‐1 h‐1) or (‐)isoprenaline (100 micrograms kg‐1 h‐1) increased reactivity of the airways to histamine or bombesin to a comparable extent. 5. Neither adrenaline (100 micrograms kg‐1 h‐1) nor forskolin (600 micrograms kg‐1 h‐1) increased reactivity of the airways to histamine or bombesin. 6. Intravenous infusion of dopamine (100 micrograms kg‐1 h‐1) or noradrenaline (100 micrograms kg‐1 h‐1) increased reactivity of the airways to histamine or bombesin. 7. Intravenous infusion of (+/‐) propranolol (100 micrograms kg‐1 h‐1) increased reactivity of the airways to histamine or bombesin which was partially inhibited by bilateral vagal section. 8. Depletion of circulating platelets by lytic anti‐platelet serum or concomitant infusion of an antagonist of platelet‐activating factor (PAF), ginkgolide B (1 mg kg‐1 h‐1) did not diminish the capacity of (+/‐)isoprenaline (100 micrograms kg‐1 h‐1) to induce hyperreactivity of the airways to histamine or bombesin. 9. These observations indicate that (+/‐)isoprenaline can induce airway hyper‐reactivity by a mechanism unrelated to beta‐adrenoceptor activation, but which is dependent upon intact vagus nerves.

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