Augmentation of bethanechol-stimulated gastric secretion by lowering body temperature in water-immersed rats

The present study was designed to elucidate influences of hypothermia on gastric secretory response to secretagogues (bethanechol, histamine and tetragastrin) in rats exposed to restraint plus water immersion (36 and 25 degrees C) stress. In vagotomized rats provided with a pH microelectrode, decrease in intragastric pH by bethanechol (75 micrograms/kg, i.p.) was markedly produced under the water-immersion at 25 degrees C and the extent of the pH decrease was significantly greater than that observed under the water-immersion at 36 degrees C. However, intragastric pH decrease by histamine (1 mg/kg, i.v.) or tetragastrin (60 micrograms/kg/20 min, i.v.) was not affected by varying water temperatures. Using a technique of pyloric ligation, gastric acid and pepsin responses to bethanechol were measured at doses of 50-100 micrograms/kg in vagotomized rats and also at doses of 0.5-1.0 mg/kg in vagally intact rats. Stimulation of acid and pepsin secretion by bethanechol was provoked only under the water-immersion at 25 degrees C. As compared with the values obtained under the water-immersion at 36 degrees C, a significant augmentation of bethanechol-stimulated secretion was seen for acid and pepsin output in vagotomized rats and seen for acid output in vagally intact rats under the water-immersion at 25 degrees C. These results suggest that hypothermia may operate some mechanism for increasing the secretory responsiveness of the stomach to cholinomimetics.