ACTIONS OF MOGUISTEINE ON COUGH AND PULMONARY RAPIDLY ADAPTING RECEPTOR ACTIVITY IN THE GUINEA PIG

Abstract With anaesthetized guinea pigs, the actions of moguisteine were tested on the cough reflex, the resting discharge of lung rapidly adapting receptors (RARs), RAR activity induced by aerosols of capsaicin, stimulation of RARs due to i.v. injection of capsaicin, and on the reflex responses to i.v. capsaicin. I.v. moguisteine (20 gm gkg −1 ), compared with vehicle, decreased the spontaneous firing of RARs. Intragastric (i.g.) moguisteine (200mgkg −1 ) had no effect on resting discharge. I.g. moguisteine depressed the cough response due to capsaicin aerosol (0.01–1mgml −1 ) and significantly reduced the increased discharge of the RARs due to the aerosol. I.v. and i.g. moguisteine reduced the proportionate increase in RAR discharge due to i.v. capsaicin (50 gm gkg −1 ). It did not appreciably affect the cardiovascular and respiratory responses to i.v. capsaicin, which presumably activated lung C-fibre receptors. We conclude that the antitussive action of moguisteine is mediated at least in part by a decrease in the excitatory response of RARs to tussive stimuli.