Recently interest in investigations of adrenergic agents (stimulants and inhibitors) on gastric secretion, motility, and ulceration in experimental animals has increased (1-7). Pradhan and Wingate (6) have demonstrated that phentolamine and tolazoline enhanced the spontaneous gastric secretion in dogs while phenoxybenzamine and dichloroisopro terenol showed inhibitory effects on spontaneous as well as induced secretion by food, bethanechol, and histamine. Bass and Patterson (3) have shown that both adrenergic and adrenergic blocking agents (including phentolamine and tolazoline) possessed anti secretory properties on rat gastric secretion. Hence, if gastric acid is a primary element in experimental ulcer, adrenergic and adrenergic blocking aegnts which have antisecretory effect should inhibit gastric ulceration. However, phentolamine, MJ 1999, and isopro terenol did not affect the incidence of histamine-induced ulcer in guinea pigs (6). More over, propranolol and phenoxybenzamine increased the incidence of ulceration in fasted rats immobilized for 8 hours (7). In this study, therefore, an attempt was made to in vestigate the effect of several adrenergic blocking agents on gastric secretion and stress induced ulcer in rats and to clarify a part of the mechanism of gastric ulceration by stress.
METHODSGastric secretion studies: Male Donryu strain rats (200-230 g) were used in the follow ing experiments. The animals were deprived of food for 24 hours in individual cages prior to the experiment but were allowed free access to water. Under ether anesthesia, the abdomen was incised and the junction between the pylorus and duodenum was ligated, as described by Shay et al. (8). Four hours later, the animals were killed by a blow on the head and the stomach was removed. Gastric juice was collected in a graduated test tube and the total acidity was determined by titration with 0.1 N NaOH using phenol phthalein as an indicator. The pH was determined with a glass electrode.Stress ulcer studies: As described previously by Takagi and Okabe (9), animals (235 255 g) were placed in a stress cage and immersed into a water bath (23°C) for 7 hours to the level of xiphoid process. At the end of the stress, the animals were killed by a blow * Present address: