Central nervous system actions of beta-endorphin on gastric acid secretion

We assessed the central nervous system (CNS) actions of beta-endorphin on gastric acid secretion in awake dogs. Synthetic beta-endorphin (0.2-2.0 nmol X kg-1), but not Leu- or Met-enkephalin, microinjected into the third cerebral ventricle, significantly (P less than 0.01) decreased gastric acid secretion stimulated by pentagastrin. beta-Endorphin given intracerebroventricularly inhibited gastric acid secretion following 2-deoxy-D-glucose (P less than 0.01), but not after stimulation with histamine. Intravenous administration of beta-endorphin did not inhibit gastric acid secretion. beta-Endorphin decreased gastric acid secretion but not the concomitant release of gastrin stimulated by a 200-ml liquid meal containing 8% peptone. Pretreatment of the animals with the opioid antagonist, naloxone, prevented the gastric inhibitory effect of beta-endorphin. Furthermore, either ganglionic blockade with chlorisondamine or truncal vagotomy completely abolished the gastric inhibitory action of beta-endorphin. These findings indicate that beta-endorphin, but neither Leu- nor Met-enkephalin, acts within the CNS to inhibit gastric acid secretion in awake dogs. beta-Endorphin-induced inhibition of gastric acid secretion is mediated by an opiate-dependent pathway and by the autonomic (parasympathetic) nervous system.