Mechanisms for regulation of gastrin and somatostatin release from isolated rat stomach during gastric distention

AIM: To investigate the intragastric mechanisms for regulation of gastric neuroendocrine functions during gastric distention in isolated vascularly perfused rat stomach. METHODS: Isolated vascularly perfused rat stomach was prepared, then the gastric lumen was distended with either 5,10 or 15 ml pH7 isotonic saline during a period of 20 min. During the distention, the axonal blocker tetrodotoxin (TTX), the cholinergic antagonist atropine, or the putative somatostatin-antagonist cyclo (7-aminoheptanoyl-Phe-D-Trp-Lys-Thr(Bzl)) were applied by vascular perfusion. The releases of gastrin and somatostatin were then examined by radioimmunoassay. RESULTS: The graded gastric distention caused a significant volume-dependent decrease in gastrin secretion (-183+/-75 (5 ml), -385+/-86 (10 ml) and -440+/-85 (15 ml) pg/20 min) and a significant increase of somatostatin secretion (260+/-102 (5 ml), 608+/-148 (10 ml) and 943+/-316 (15 ml) pg/20 min). In response to 10 ml distention, the infusion of either axonal blocker TTX (10(-6) M) or cholinergic blocker atropine (10(-7) M) had a similar affect. They both attenuated the decrease of gastrin release by approximately 50 %, and attenuated the increase of somatostatin release by approximately 40 %. The infusion of somatostatin-antagonist cyclo (7-aminoheptanoyl-Phe-D-Trp-Lys-Thr (Bzl)) (10(-6)M) attenuated the decrease of gastrin release by about 60 %. Furthermore, combined infusion of the somatostatin-antagonist and atropine completely abolished distention-induced inhibition of gastrin release. CONCLUSION: The present data suggest that distention of isolated rat stomach stimulates somatostatin release via cholinergic and non-cholinergic TTX-insensitive pathways. Both somatostatin and intrinsic cholinergic pathways are responsible for distention-induced inhibition of gastrin release.