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Role of platelet activating factor (PAF) on the formation of rat ischemic colitis was investigated. High incidence of the formation of ischemic colitis was observed after ligation of marginal vessels of the rat with stricture of the rectum, however, administration of PAF-inhibitor (TCV) decreased incidence of the lesion. Only the lesion in the mucosa occurred after clamping of the marginal vessels of the rat with stricture of the rectum and administration of TCV did not affect the incidence of the lesion. In conclusion, the etiological involvement of PAF on deterioration of the ischemic colitis was suspected.

The inhibitory mechanism of dopamine (DA) on rat gastric motility was investigated in association with DA receptors. Gastric movement was assessed according to the method of Jacoby et al and was expressed with the system of Ludwick et al. (1968). DA inhibited gastric movement in both the corpus and antrum in a dose-dependent manner. Domperidone, a specific antagonist of DA2 receptor, suppressed DA-induced inhibition of gastric movement in a dose-dependent manner. SCH23390, a specific antagonist of DA1 receptor did not affect DA-induced inhibition of gastric movement. LY171555, a specific agonist of DA2 receptor, inhibited gastric movement in both the corpus and antrum in a dose-dependent manner. SKF38393, a specific agonist of DA1 receptor, did not affect gastric movement. These results indicate that DA plays an important role in the inhibitory regulation of gastric motility, through DA2 receptor but not DA1 receptor.

Preventive effect of dopamine on stress ulcer formation was investigated in rats. Dopamine 1-10 micrograms/kg/min suppressed the elevation of ulcer index significantly after water immersion and restraint stress in a dose-dependent fashion, however ulcer indices of 25 micrograms/kg/min of dopamine were higher than 10 micrograms/kg/min. Dopamine 1-10 micrograms/kg/min suppressed the decrease of gastric mucosal blood flow, gastric mucosal prostaglandin E2 content and gastric transmucosal potential difference during stress loading in a dose-dependent manner, although the suppression of them in 25 micrograms/kg/min of dopamine was smaller than in 10 micrograms/kg/min also. Dopamine suppressed the increase of gastric acid secretion and gastric motility during stress loading in a dose-dependent fashion up to 25 micrograms/kg/min. These results indicates that dopamine suppresses the formation of stress ulcer by increasing defensive factors and decreasing aggressive factors.