[Actions of drugs affecting the cough reflex]

Authors evaluated the part of some receptor systems in the antitussive activity of drugs.

The cough was induced by mechanical stimulation of the airways. Unanesthetized cats were used in this study.

They followed: 1. statistically highly significant decrease of cough parameters after administration the drugs influencing the different types of opiate receptors--tramadol, tilidine, pentazocine, codeine and butorphanol. Every of these drugs were administered in a dose 10 mg/kg b.w. intraperitoneally, 2. the antitussive activity of codeine was decreased by pretreatment with naloxone only in part, 3. selective antagonist 5-HT2 receptors ketanserine (1 mg/kg b.w.) decreased antitussive effect of codeine by 10% and effect of tramadol by 20%, 4. the ability of codeine to reduce the cough parameters was unchanged after pretreatment with haloperidol (0.1 mg/kg b.w.), 5. whereas the pretreatment with reserpine decreased the cough-suppressing effect of codeine, 6. the application of gabaergic agent gabalid leads to the highly significant decrease the cough parameters. Results of these experiments showed that gaba-ergic mechanism might be involved in the mechanism of action of narcotic antitussives agents, 7. we showed, that inhibition of glutaminergic synaptic transmissions afferent impulses from cough receptors with dextromethorphan leads to suppressing cough reflex in cats.

Antitussive activity of agents is not only mediated by means of mí opiate receptors. The results suggest, that gabaergic, serotoninergic systems and activity of NMDA receptors play an important role in the mechanism of action of antitussive drugs. Decrease in levels of brain monoamines modifies the cough-depressant effect of codeine. (Fig. 7, Ref. 23.)