H1- and H2-receptor influences of histamine and ammonia on rapidly adapting pulmonary stretch receptor activities.

Studies were designed to establish the difference of the excitatory mechanisms between histamine and ammonia on rapidly adapting pulmonary stretch receptors (RARs). We therefore examined the responses of RARs to histamine administered as an aerosol and ammonia inhaled as a vapor before and after aerosol administration of mequitazine or cimetidine in spontaneously breathing rabbits. The excitatory responses of RARs to aerosols of histamine at different concentrations were completely blocked by administration of aerosol mequitazine but potentiated by aerosol cimetidine. However, the increases of RAR activity produced by inhalation of ammonia vapor at different concentrations were not significantly affected by aerosol administration of either a H1-receptor blocker or a H2-receptor antagonist. These results suggest that the stimulation of RARs by aerosol histamine occurs as a result of the interaction between H1 (excitatory)- and H2 (inhibitory)-receptor effects, whereas these two receptor effects do not contribute to the ammonia-induced RAR stimulation.