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'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.