Dopaminergic modulation of rectosigmoid motility: action of domperidone

To investigate the role of dopamine in the modulation of colonic motility we evaluated the effect of dopamine on basal rectosigmoid motor activity before and after treatment with domperidone, phentolamine, propranolol, atropine or placebo in 12 healthy subjects. We also investigated the role of dopamine on the postprandial gastrocolic response. Basal motility index was 126 +/- 38. Dopamine (5-100 micrograms/kg) generated dose-dependent contractions with a frequency of 3 cpm. At 50 micrograms/kg dopamine produced a motility index of 2066 +/- 631. Pretreatment with domperidone (0.4 mg/kg) significantly decreased the amplitude of contractions induced by dopamine but had no effect on the frequency. The motility index was reduced to 668 +/- 148. In contrast atropine, phentolamine and propranolol had no effect on dopamine-stimulated motility. Furthermore, domperidone significantly attenuated the postprandial gastrocolic response compared to placebo. The motility indices of the early and late gastrocolic response were reduced by 65 +/- 12 and 70 +/- 10% of control, respectively. These studies indicate that dopamine stimulates rectosigmoid motility in contrast to its known inhibitory effect on upper gastrointestinal motility. This appears to be mediated by specific dopamine receptors.