Effect of Dopamine on Bethanechol-Stimulated Gastric Mucosal Blood Flow and Gastric Acid Secretion in Dogs with Gastric Fistula

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Abstract
The aim of the present study was to investigate the effect of dopamine on bethanechol-stimulated gastric acid secretion and mucosal blood flow. Dopamine was used alone and in conjunction with selective blockade of the α, β, and dopaminergic receptors. An increasing and dose-dependent stimulation of gastric acid secretion was found for dopamine at 1, 5, and 10 μg/kg/min. A significant inhibition of gastric acid secretion was found with the highest dose of dopamine (40 μg/kg/min). The stimulatory effect seems to be mediated by more than one receptor, whereas the inhibition by high dopamine doses could be explained by a β1 stimulation. Dopamine (10 μg/kg/min) was found to increase the bethanechol-stimulated gastric mucosal blood flow. Phentolamine (α blockade) increased this dopamine-elevated blood flow further, with a significant increase in the ratio between blood flow and acid secretion, indicating a primary action of the α receptors on blood flow. Bethanechol stimulated the gastric acid secretion and blood flow in a parallel manner. It is concluded that α-receptor stimulation is the predominant directly acting factor in the regulation of gastric mucosal blood flow, whereas stimulation of β, muscarinic, and ‘gastrinergic’ receptors mainly occurs indirectly via changes in parietal cell function. The main effect of dopamine seems to be on gastric motility, whereas the effect on gastric acid secretion is of minor importance.