It has been reported that serotonin given intravenously inhibits pancreatic exocrine secretion even though some serotonin antagonists do not modify the seratonin action. It has been also published that the central serotonergic system exerts stimulatory role in pancreatic exocrine secretion.
Therefore, the present study was performed to verify the action of endogenous serotonin and the central serotonergic system on pancreatic exocrine secretion by means of β-chlorophenylalanin(PCPA) that has been known to block tryptophan hydroxylase activity. Rats were intraperitaneally injected with PCPA at a concentration of 300mg/kg and then fasted for 24 hours with free access of water. Pancreatic juice was collected from the rats under urethane anesthesia and then volume flow, bicarbonate output, chloride output and amylase output were measured.
1. PCPA profoundly increased the volume flow, bicarbonate output and chloride output but remarkably inhibited the amylase output.
2. Neither atropine nor phentalamine affected the PCPA action.
3. Propranolol significantly reduced only the bicarbonate induced by PCPA.
4. The plasma concentrations of catecholamines were riot changed after injection of PCPA.
5. The plasma secretin concentration was not altered after PCPA injection.
6. Cyproheptadine, a serotonin receptor antagonist. did not change the spontaneous pancreatic exocrine secretion.
7. A light-microscopic examination reveals severe lass of zymogen granules in the acinar cells of the PCPA-treated rats.
Therefore, it is concluded from the present study that endogenous seratonin and the central serotonergic system do not seem to exert a regulatory role in spontaneous pancreatic exocrine secretion, and that PCPA change the pancreatic exocrine secretion, probably by acting an the acinar cells directly.
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