morphine and apomorphine inhibit gastrointestinal transit (git) through two different mechanisms

morphine was used as a remedy for the control of diarrhea centuries before it&apos;s sedative-analgesic effect was discovered. although several mechanisms have been proposed for the morphine-induced inhibition of gastrointestinal transit (oit), the exact mechanism has not yet been identified. on this basis the possible involvement of the dopaminergic system in morphine-induced inhibition of transit was investigated. this study showed that morphine decreased gastrointestinal transit (oit) of charcoal dust in mice.in a dose-dependent manner. the response was inhibited by the opiate antagonist naloxone. pretreatment of animals with the d-2 antagonist sulpiride or the peripheral dopamine antagonist domperidone did not alter the morphine-induced inhibition of oit. the d-l/d-2 agonist apomorphine also decreased oit in mice. the response was inhibited by sch 23390 or sulpiride pretreatment (p<0.01), but not by domperidone or naloxone. it is concluded that morphine and apomorphine inhibit oit through opiate and dopaminergic mechanisms, respectively.