Morphine reduces vagal-stimulated gastric acid secretion through a central action.

The influence of morphine on gastric acid secretion stimulated by 2-deoxy-D-glucose or electrical vagal stimulation was studied in anaesthetised rats with perfused stomachs. It was found that changes in gastric acid output induced by electrical vagal stimulation were not noticeably affected, whereas those evoked by 2-deoxy-D-glucose were significantly suppressed by morphine pretreatment. The depressant effect of the opiate on the acid secretion stimulated by 2-deoxy-D-glucose was abolished by naloxone pretreatment. It is suggested that morphine inhibits vagal-stimulated gastric acid secretion in rats by acting predominantly on opioid receptors in the central nervous system.