Japan. J. Pharmacol.44, 63-69 (1987) 63 Stimulatory Effect of Pentobarbital and Some Anesthetics on Gastric Secretion in the Continuously Perfused Stomach in Rats Under Urethane Anesthesia Kazuo WATANABE, Shingo YANO and Wen-Chuan LIN Departmentof Drug Evaluationand ToxicologicalSciences, Facultyof PharmaceuticalSciences, Chiba University,Yayoi-cho 1-33, Chiba 260, Japan Accepted February2, 1987 Abstract-Effects of some anesthetics (pentobarbital, thiopental, alpha-chloralose and urethane) on gastric acid secretion were studied in the continuously perfused stomach in rats. Under urethane anesthesia, pentobarbital, thiopental and alpha chloralose showed a definite stimulation on gastric acid secretion. Pretreatment with atropine or hexamethonium abolished the pentobarbital-induced acid secretion. Pentobarbital and thiopental did not elicit acid secretion in bilateral truncal vagotomized rats. In spinal rats, pentobarbital also stimulated acid secretion, but urethane, which was subcutaneously administered, reduced spontaneous acid output. The present results indicated that some anesthetics could stimulate gastric secretion in the anesthetized rat in contrast to the previously described inhibitory effect in the Shay rat. In studies on gastric acid secretion, Co., Ltd., Japan). Rats were fasted for 24 hr pylorus-ligated rats, so called Shay rats, and before each experiment, but allowed free fistula-provided animals have been used, and access to water. it is generally considered that general anes Experiments were carried out on both thetics such as barbiturates (1-3), alpha anesthetized rats and spinal rats. Animals chloralose (1) and urethane (1, 4, 5) reduced were anesthetized with 1.35 g/kg urethane, gastric acid secretion. However, some i.p., or transected at the C1-C2 spinal level investigators reported stimulatory action by under ether anesthesia. Cannulation of the barbiturates (6-8) or by alpha-chloralose (8 femoral vein was used for administration of 10). In addition, others described no secretory drugs. Rectal temperature was maintained at action of barbiturates (9, 11 ) or alpha 36±1 °C by intermittent heating with an chloralose (12). In the course of our research infrared lamp. After spinal transection, on the control mechanisms of gastric acid spinal rats were artificially respired with room secretion in the central nervous system, we air and ether anesthesia was immediately occasionally observed the stimulatory effect stopped. More than 30 min later, the stomach of pentobarbital in the perfused stomach perfusion was then started. After operation, preparation in urethane anesthetized rats. In lidocaine ointment was dermally applied to the present paper, we compared the effect of the injured portions of spinal rats. pentobarbital with that of several other Gastric acid secretion assay was performed anesthetics on gastric acid secretion. following the procedure as described by Watanabe and Goto (13) with a slight Materials and Methods modification (14). A dual polyethylene gastric Male Wistar rats weighing 220-270 g cannula was inserted into the gastric lumen were used. The animals were housed under after ligation of the pylorus and esophagus, controlled environmental conditions (24+ keeping the vagus nerve intact. The inlet and 1 °C, illuminated between 07:00-19:00) and the outlet tubes of the dual cannula were fed on commercial rat chow (Oriental Yeast connected to a saline reservoir, and the 64 K. Watanabe, S. Yano & W.-C. Lin stomach was continuously perfused with a and histamine dihydrochloride (Wako). All saline solution (pH was adjusted to 5.0) compounds were dissolved in saline except through the gastric cannula by means of a urethane which was dissolved in distilled perfusion pump at the rate of 5 ml/min. The water. When the higher dose of pentobarbital perfusate was titrated automatically in the was needed, pentobarbital sodium was reservoir with 0.01 N NaOH at pH 5.0 using dissolved in propylene glycol, 40 v/v%, and the titrator (HS-2A; TOA Electronics, Ltd., alcohol, 10.5 v/v% (50 mg in 1 ml). Alpha Japan) connected to a DC recorder (Mode 1 chloralose or thiopental sodium was prepared EPR-3T; TOA Electronics, Ltd., Japan). The 10 min before administration. Doses of acid amount of the perfusate during a period drugs were expressed as the amount of the of 2 min was continuously recorded by salt. using a zero suppression adapter (TOA Electronics, Ltd., Japan). The acid amount of Results the secreted acid was expressed in terms of 1. Effect of pentobarbital, thiopental and ,aEq/10, 30 or 60 min per animal. alpha-chloralose on gastric acid secretion of Drugs used were pentobarbital sodium perfused stomach in rats under urethane (T.C.I.), thiopental sodium (Green Cross), anesthesia: Under urethane anesthesia, basal alpha-chloralose (Nakarai), atropine sulfate acid secretion was kept rather low during an (Wako), hexamethonium chloride (Wako) experimental period of at least 6 hr, and Fig. 1. Stimulation of perfused gastric acid secretion by intravenous administration of pentobarbital (30 mg/kg), thiopental (30 mg/kg) and alpha-chloralose (40 mg/kg) and by subcutaneous administration of histamine (10 mg/kg) in urethane anesthetized rats. Ordinate scale: rate of acid secretion per two minutes. Intragastric perfusate was titrated with 0.01 N NaOH. The titrated volume of the NaOH solution was recorded and expressed on terms of qEq H+/2 min. Abscissa scale: chart speed was 30 mm/30 min . PENT: pentobarbital, TP: thiopental, CHL: alpha-chloralose and HIS: histamine . Pentobarbital-Induced Gastric Acid Secretion 65 Table 1. Effect of pentobarbital, thiopental, alpha -chloralose and histamine on gastric acid secretion of perfused stomach in rats under urethane anesthesia Basal level was 3 times the amount of 10-min before drug treatment. *P<0.05, **P<0.01, ***P<0.001, compared with the basal level by the paired t-test. saline did not influence the basal gastric resulted in a decrease in mean blood pressure secretion. Intravenous administration of pen (about 60 mmHg in maximal fall) and heart tobarbital, thiopental and alpha-chloralose rate (about 60 bpm in maximal reduction) definitely stimulated acid secretion (Fig. 1, followed by return to control values in about Table 1). The stimulating effect of pen 20 min. The respiration was transiently tobarbital (30 mg/kg), thiopental (30 mg/kg) depressed immediately after pentobarbital and alpha-chloralose (40 mg/kg) began administration. about 10 min after administration, and 2. Effect of atropine, hexamethonium or maximal acid output was observed about 20 bilateral truncal vagotomy on pentobarbital min after injection. The duration of pen induced acid secretion of perfused stomach tobarbital-induced acid output was about one in rats under urethane anesthesia: Atropine hour. In these experiments, the variation of (1 mg/kg, i.v.) or hexamethonium (5 mg/kg, the responses had a rather wide range. Intravenous administration of pentobarbital (30 mg/kg) in urethane-anesthetized rats Fig. 3. Effect of bilateral truncal vagotomy on pentobarbital-induced acid secretion of perfused stomach in rats under urethane anesthesia. -/-: intact rat, treated with pentobarbital 30 mg/kg, i.v., Fig. 2. Effect of atropine or hexamethonium on n=16; -s-: vagotomized rat, treated with pen pentobarbital-induced acid secretion of perfused tobarbital, 30 mg/kg, i.v., n=6; -0-: vagotomized stomach in rats under urethane anesthesia. CON: rat, treated with saline 0.2 ml/100 g, i.v., n=5; control (pentobarbital 30 mg/kg, i.v., n=16), ATR: histamine (10 mg/kg, s.c.) was given to vago pretreated with atropine (1 mg/kg, i.v., n=5), HEX: tomized rat after 30 min of pentobarbital adminis pretreated with hexamethonium (5 mg/kg, i.v., n=6). tration, to check peripherally stimulated acid Each column represents the mean ±S.E. ***P<0.001, response. Each point represents the mean±S.E. compared with the control group by Student's **P<0 .01, ***P<0.001, compared with the intact t-test. rat group at the same period by Student's t-test. 66 K. Watanabe, S. Yano & W .-C. Lin then gradually increased and became maximal after 1-1.5 hr of perfusion. To avoid the influence of excess water, intravenous admin istration of pentobarbital, which was dissolved in propylene glycol and alcohol, to spinal rats significantly increased the acid output (Fig. 4). Urethane resulted in inhibition of basal gastric acid secretion at the 60-90 min period after subcutaneous administration (1.35 g/kg) to spinal rats (control group: 59.36±14.73 uEq, urethane group: 15.03± 8.85 ,iEq, *P<0.05). After 90 min, the amount of acid secretion of urethane treated rats tended to be decreased compared with that of the control group. -. _.. r.,...,....._.. Fig. 4. Effect of intravenous administration of Discussion pentobarbital on acid secretion of perfused stomach in spinal rats. Pentobarbital was injected at 2.5 hr The results presented in this report after perfusion. -o-: control, n=4; -/-: vehicle indicated that pentobarbital, thiopental and (containing propylene glycol, 40 v/v%, and alcohol, alpha-chloralose stimulated gastric acid 10.5 v/v%), 0.1 ml/100 g, n=5; -0-: pentobarbital , secretion in the continuously perfused rat 50 mg/kg, n=6; -~ pentobarbital, 30 mg/kg, stomach, while urethane decreased acid n=5. Each point represents the mean±S.E. *P<0.05, output. **P<0 .01, compared with the amount of 10-min In 1967, Lee and Thompson (1) reported before pentobarbital treatment by the paired t-test. that maximal histamine-induced gastric acid secretion in Shay rats was depressed by i.v.) given 10 min before intravenous pen general anesthetics such as pentobarbital, tobarbital (30 mg/kg) abolished the pen alpha-chloralose and urethane when com tobarbital-induced acid secretion (Fig. 2). pared to the control rats (they were operated Bilateral truncal vagotomy was performed at under local anesthesia with 2% procaine). the gastro-esophagus junction, and sero However, in 1973, Ozturkcan (11) reported muscular myotomy was also operated at the that under similar experimental conditions, lower end of the esophagus to ensure cutting ether, urethane or pentobarbital altered of division of intramural fibers.