Effects of ammonia and histamine on lung irritant receptors in the rabbit

The effects of ammonia and histamine on the responses of rapidly adapting pulmonary stretch receptor (RAR) activity before and after administration of isoprenaline or atropine were studied in spontaneously breathing rabbits. Inhalation of vapor from 15% ammonia solution increased the activity of RARs and this increased activity was not significantly altered by isoprenaline (50 micrograms/kg) or atropine (0.3 mg/kg). The RARs increased their activity following intravenous injections of histamine (20, 40 and 60 micrograms/kg). The excitatory responses to histamine at different doses were blocked by prior treatment with isoprenaline (50 micrograms/kg). In 8 of the tested 11 different RAR preparations on 11 rabbits, atropine (0.3 mg/kg) greatly diminished the increases of RAR activity produced by histamine at different doses. These results suggest that the ammonia-induced RAR stimulation results in a direct action of the endings whereas the activation of RARs by histamine is probably due to the combined influence of both local airway constriction and postganglionic parasympathetic pathway-mediated bronchoconstriction.