STUDIES OF HISTAMINE, H1 AND H2 RECEPTORS IN BRONCHOCONSTRICTION

Abstract

To clarify the roles of H1 and H2 receptors in the airways of asthmatic patients, we studied the effects of the administration of a histamine H1 receptor antagonist, an H2 receptor antagonist and a combination of both on bronchial constriction induced by histamine inhalation and allergen inhalation in patients with asthma.We also examined the effects of H1 and H2 antagonists on bronchial response induced by histamine inhalation in normal guinea pigs.Chlorpheniramine (H1 antagonist) raised the threshold of histamine-induced bronchoconstriction in asthmatic patients compared with that at no medication. In contrast, cimetidine (H2 antagonist) augmented histamine-induced bronchospasm. The combination of both produced inhibitory effects similar to those of chlorpheniramine alone.These findings imply that in asthmatic patients histamine induces bronchial constriction predominantly via H1 receptors in the airways, but H2 receptors may function to induce bronchodilation.In guinea pigs, histamine-induced bronchial response was reduced after the administration of H1 antagonist, but no effects of H2 antagonist were observed.Chlorpheniramine alone also had an inhibitory effect on the immediate asthmatic response (IAR) of the allergen inhalation test. Cimetidine did not have any clear influence on IAR.It is suggested that both H1 and H2 receptors are present in the airways of humans, and histamine action via the H1 receptors plays the main role in the development of bronchoconstriction.