In our previous papers (1, 2), we reported that a new fraction of licorice root (FM 100) showed a protective effect on ulceration in the pylorus ligated rats and gastric antisecretory activities in rats and dogs in spite of being devoid of anticholinerigc properties. FM 100 decreased non-stimulated gastric secretion volumes and acid outputs in the pylorus ligated rats and gastric acid secretion induced by instillation of peptone into the antrum separated from the fundus in acute fistula rats. Effects of histamine and methacholine on gastric secretion were partially antagonized by FM 100. On the contrary, F.100 did not exert the inhibitory action on secretion induced by crude gastrin. Then, we propounded the hypothesis that the mechanism of gastric antisecretory activity of FM 100 is probably due to inhibitory action of the release of gastrin from the antral mucosa.The aim of the present investigation was to study the mechanism of gastric antisecretory activity of F000, especially concerning the mechanism of the release of gastrin from the antral mucosa of the rat.
MATERIALS AND METHODSMale Donryu rats weighing about 200 g were used for acute experiments. They were deprived of food before use but allowed free access to water overnight. Male Wistar rats weighing above 250 g were used for the preparation of chronic fistula rats . Acute fistula rats The surgical procedure was described in the previous paper (2). The gastric juice was washed out with 10 ml of saline every hour and the washing solution was titrated with 0.1 N NaOH using phenolphthalein as indicator. The acid outputs were expressed in ml of 0. 1 N HCl per hour. For stimulation of gastric secretion, intramuscular injection of gastrin like tetrapeptide (AOC-TP : t-amyloxycarbonyl Trp. Met. Asp . Phe. NH, (3) ; 500 sag/kg, i.m.), intragastric instillation of 1 ml of 20% ethanol or 1 % acetylcholine solu tion or mechanical stimulation (gastric distension induced by intragastric instillation of 10 ml of saline) were employed.
Pylorus ligated rats (Shay rats)The surgical procedure of the pylorus ligated rats was identical to the method des cribed in the previous paper (2). The time of pyloric ligation was set at 4 or 5 hours . In the study of the effect of antrectomy on gastric secretion, the antral region was resected when the pylorus was ligated.