Variations in Gastric Tone Associated with Duodenal Motor Events After Activation of Central Emetic Mechanisms in the Dog

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Abstract
To define the variations in gastric tone associated with the intestinal motor correlates of vomiting, we studied the effects of intracerebroventricular pharmacological manipulation in four fasting, conscious dogs with an injection catheter implanted into the fourth cerebral ventricle. Simultaneous monitoring of gastric tone and duodenal motility allowed us to study the correlation between gastric and duodenal motor events. We compared the effects of i.c.v. morphine (0.1 to 1 μLg/kg), apomorphine (0.003 to 0.03 (μg/kg), and the α2‐adrenoceptor agonist ST91 (0.1 to 1 μg/kg). These agonists, by the i.c.v. route all induced gastric relaxation accompanied by a retrograde power contraction in the duodenum and, at the highest doses, emesis; subsequently, a burst of intense phasic pressure activity developed in the duodenum. However, at a dose that was fully effective i.c.v., they had no effect when given intravenously. Naloxone or domperidone, at doses that had no effect per se, blocked the effects of morphine and apomorphine, respectively, except for a residual gastric relaxation. Idazoxan failed to block the effects of ST91. We conclude that a common pattern of motor events is triggered in the upper gut by different drugs by activation of receptors involved in the mechanism of vomiting and probably located in the central nervous system, and that the effects of morphine and apomorphine are mediated respectively by opioid and dopamine receptors.