Role of dopamine receptors in gastrointestinal motility

Apomorphine (3.5 and 10 mg/kg, s.c.) and morphine (1.3 and 10 mg/kg, s.c.) produced a dose-dependent decrease in gastrointestinal transit of charcoal dust in rats. The involvement of dopamine in such a constipatory effect was found to be mediated to a greater extent by DA2 than by DA1 receptors, using a specific DA1 antagonist (SCH 23390) and DA2 antagonists (alizapride, domperidone). The decrease in apomorphine (50 micrograms) and dopamine (100 and 200 micrograms)-induced gastrointestinal transit after intracisternal administration was antagonized by haloperidol. These results provide evidence for the involvement of dopamine receptors in the constipatory effects of apomorphine and morphine in rats.