Enkephalinergic control of somatostatin secretion from the perfused rat stomach

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Abstract
A role for the enkephalins in the regulation of gastric somatostatin (SLI) secretion has been investigated in an isolated perfused rat stomach model. Both methionine- and leucine-enkephalins caused a dose-dependent inhibition of gastric inhibitory polypeptide (GIP) stimulated SLI secretion. Leu-enkephalin was one order of magnitude less potent than met-enkephalin: 50% inhibition by met-enkephalin was at 4 × 10−9 M and with leu-enkephalin 3.5 × 10−8 M. Naloxone (100 nM) had no effect on basal secretion but blocked the inhibitory action of met-enkephalin (1 nM or 1 μM). Vagal stimulation (7 V, 10 Hz, 5 ms) inhibited GIP-stimulated SLI release. Administration of naloxone partially reversed this inhibition, suggesting that endogenous opioids were at least partially responsible for vagally induced inhibition. A number of possible pathways by which endogenous enkephalins may modulate SLI release have been proposed.