Inhibitory Action of Exogenous Serotonin on the Pancreatic Exocrine Secretion in Rats

초록

Serotonin (5-HT) is synthesized and released from enterochomaffin cells in the gastrointestinal mucosa and platelets. Most of these serotonins are existed in the gastro-intestine, and only few amounts are existed in the central nervous system. Although most of serotonins are existed in the gastrointestinal tract, a role of serotonin in the gut is still unclear.We previously reported that electrical field stimulation (EFS)- evoked pancreatic volume flow and amylase output further elevated by spiperone hydrochloride, serotonin (5-hydroxytryptamine, 5-HT) antagonist, in the isolated rat pancreas. This study was aimed to investigate roles and the action mechanisms of exogenous serotonin and serotonergic nerves on pancreatic exocrine secretion using the two experimental models (in vivo and exo vivo model). Results of exo vivo experiment: CCK elevated pancreatic volume flow and amylase output in rats. Endogenous insulin released by glucose potentiated the action of CCK. CCK-stimulated pancreatic volume flow and amylase output were not change by exogenous serotonin under hypoglycemic condition. However, exogenous serotonin significantly inhibited CCK-stimulated pancreatic volume flow and amylase. Results of in vivo experiment: CCK elevated pancreatic volume flow and amylase output in the isolated perfused rat pancreas. Endogenous insulin released by 18mM glucose potentiated the action of CCK. CCKstimulated pancreatic volume flow and amylase output were not change by exogenous serotonin under 5.6 mM glucose backgroud. However, exogenous serotonin significantly inhibited potentiated the action of CCK by insulin. These observations are good agreement with our previous in vitro results and strongly indicate that serotonin play a inhibitory role in pancreatic exocrine secretion and insulin may be involved the inhibitory actions.

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