Histamine-Induced Increase in Isometric Tension of Smooth Muscle Is Mediated by Local Vagus Nerve in Human Bronchus

Abstract

Background: The vagus nerve is reported to play an important role in the regulation of airway responsiveness. Objective: In the present study, we investigated the role of the local vagus nerve in the changes in isometric tension of smooth muscle induced by histamine in the human airway. Methods: Eight human lung tissue specimens were obtained at thoracic surgery, and 24 bronchial smooth muscle strips were used for isometric tension recording. The changes in isometric tension were induced by histamine in the presence or absence of physostigmine (10^–6 M), atropine (10^–6 M), and/or tetrodotoxin (10^–6 M). Results: We found that: (1) histamine induced a dose-dependent increase in the isometric tension in human bronchial smooth muscle; (2) physostigmine (10^–6 M) significantly potentiated the amplitude of the histamine-induced increase in isometric tension; (3) atropine (10^–6 M) significantly suppressed the histamine-induced increase in isometric tension; (4) tetrodotoxin (10^–6 M), did not affect the histamine-induced increase in isometric tension of smooth muscle, and (5) in the presence of tetrodotoxin, atropine significantly suppressed the histamine-induced increase in isometric tension. Conclusion: These findings suggest that the histamine-induced increase in isometric tension is mediated partly by acetylcholine, presumably released by the direct action of histamine on the vagus efferent nerve terminals without the central reflex via vagus nerve.