The effects of H1- and H2-receptor agonists and antagonists on total lung resistance, dynamic lung compliance and irritant receptor discharge in the anaesthetized dog.

1 The effects of histamine and 4 methylhistamine (i.v.) alone, and in the presence of chlorpheniramine or cimetidine, on total lung resistance (RL), dynamic lung compliance (Cdyn) and irritant receptor activity have been studied in dogs anaesthetized with chloralose. 2 Histamine produced dose-related increases in RL and irritant receptor activity with associated falls in Cdyn which were blocked by chlorpheniramine but unaffected by cimetidine. 3 4 Methylhistamine produced small insignificant changes in RL and Cdyn and small significant increases in irritant receptor activity which were reduced with chlorpheniramine but unaffected by cimetidine. 4 The results suggest that histamine increases irritant receptor activity, either directly or indirectly, via H1-receptors.