Inhibition by morphine and morphine-like drugs of nicotine-induced emesis in cats.

The effect of morphine, methadone and pethidine injected into the cerebral ventricle of the unanesthetized cat upon emesis produced by nicotine induced similarly was investigated. Morphine and morphine-like drugs depress or abolish the emetic effect of nicotine. The inhibitory effect of morphine, methadone and pethidine is observed after a transient emetic action of these drugs. The emetic and anti-emetic action of morphine, methadone and pethidine can perhaps be ascribed to an agonist/antagonist activity. Further, the possible site of inhibitory action of morphine and morphine-like drugs on the emesis produced by nicotine may be the area postrema of fourth ventricle.