Characterization of dopamine receptor subtypes involved in experimentally induced gastric and duodenal ulcers in rats

There are conflicting reports about the role of dopamine in gastric and duodenal ulcers. This investigation was undertaken to characterize the specific subtypes of dopamine receptor involved in gastric and duodenal ulceration. Administration of dopamine D-1 agonist fenoldopam and dopamine D-2 antagonist sulpiride elicited a significant decrease in acid secretion, total acid output, pepsin output and histamine content in the gastric juice, and reduced ulcer-index values, in pylorus-ligated rats. However, dopamine D-1 receptor antagonist SCH 39166 ((-)-trans-6,7, 7a,8,9,13b-hexahydro-3-chloro-2-hydroxy-N-methyl-5H-benzo (d) naptho- (2,1-b) azepine) and the D-2 receptor agonist quinpirole led to significant augmentation of these parameters compared with respective controls. In the restraint plus water-immersion stress model the score for intraluminal bleeding and the cumulative gastric lesion length was significantly lower for rats treated with fenoldopam and sulpiride, The opposite effects were observed after pretreatment of rats with SCH 39166 and quinpirole. In the cysteamine-induced duodenal ulcer model the mean ulcer area and the score for intensity were significantly lower for fenoldopam and sulpiride and higher for SCH 39166 and quinpirole. Our data suggest that the dopamine D-1 and D-2 receptors have opposite effects on gastric and duodenal ulcers. Whereas stimulation of dopamine D-1 receptors inhibits the formation of gastric and duodenal ulcers, stimulation of dopamine D-2 receptors has a pro-ulcerogenic effect.