Effects of dopamine on the gastrointestinal tract of chicks.

The effects of dopamine on the gastrointestinal tract of chicks have been investigated. Dopamine caused concentration-related contractions of the upper oesophagus, crop or lower oesophagus but relaxed the duodenum, ileum, large intestine or caecum in a concentration-related fashion. By means of specific antagonists, the presence of muscarinic, histamine (H1), alpha-adrenergic, 5-HT-ergic and dopaminergic receptors were established in the lower oesophagus and their stimulation caused contraction while beta-adrenergic-receptor stimulation caused relaxation. Contraction of the lower oesophagus induced by dopamine was abolished by lysergic acid diethylamide and was antagonized by moderate concentrations of haloperidol or pimozide. Tachyphylaxis developed to repeated administration of a large concentration of dopamine. These findings suggest that contraction of the lower oesophagus of chicks by dopamine is largely mediated by 5-hydroxytryptamine release and that stimulation of dopaminergic receptors contributes to a lesser extent.