Antitussive Effects of Opioid Ligands

It was recently recognized that opioid receptor agonists have antitussive effects [31]. Morphine (Fig. 7) is a potent p opioid receptor agonist that exhibits marked antitussive effect, and it has been used for the treatment of severe coughs. Codeine (Fig. 7) is one of the most reliable centrally acting antitussive agents its antitussive 

T able 2 Different opioid Opioid ligand (s) Antitussive effect 

The effects of k and 8 opioid receptor activation on the cough reflex have been particularly investigated by Kamei and coworkers. They showed that U-50,488H (Fig. 7), a selective k opioid receptor agonist, suppressed the cough reflex induced by capsaicin inhalation in rats. This antitussive effect was blocked by coadministration of the k receptor antagonist, nor-BNI (Fig. 7). This suggested that the k opioid receptor had mediated the antitussive effects (Table 2) [33], 

Furthermore, Kamei et al. reported that the administration of NTI alone also produced an antitussive effect (Table 2) [36]. 

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