Time course study on the action of 5-hydroxytryptamine on gastric secretion and mucosal blood flow and on ethanol-induced gastric mucosal damage in rats.

The effects of 5-hydroxytryptamine (5-HT; given i.p. in doses of 1 or 10 mg/kg) on gastric secretion and mucosal blood flow (GMBF) and on ethanol-induced gastric mucosal damage were studied in rats over a period of 30-450 min. The blood pressure was also examined, in relation to the changes in GMBF. 5-HT, 10 mg/kg, given 30 min before ethanol administration markedly worsened lesion formation and this potentiating action was present for a further 90 min; a significant protective effect was seen only at 450 min after 5-HT injection. The lower dose of 5-HT, 1 mg/kg, did not affect the severity of gastric damage. 5-HT (10 mg/kg) also decreased GMBF at 30 min after injection and this lasted up to the end of 120 min, but the depressive action of ethanol on GMBF was reversed at 450 min. The basal gastric secretory volume was depressed from 30 to 120 min but acid output fell from 75 to 120 min after the higher dose of 5-HT; this reduction of acid secretion was followed by an increase from 360 to 450 min. 5-HT decreased the mean blood pressure in a dose- and time-dependent manner. The heart rate was unaffected by either dose level of 5-HT. The present study not only demonstrates the ulcerogenic action of 5-HT but also the protective nature of the amine. The reduction in secretory volume and lesion formation, but not acid secretion, seems to be related to GMBF depression, whereas the protective action depends on the maintenance of GMBF.