A plethysmometric method for gastric compliance studies in anesthetized rats

A new method to study gastric volume by plethysmography is presented. Twent y male Wistar rats (250-300 g) were fasted for 24 h. After anesthesia with urethane (1.2 g/kg, i.p.), a tracheostomy was performed, and cervical vesse ls were cannulated. A balloon catheter was introduced per os and positioned in the proximal stomach. The opposite end of the catheter was connected to a reservoir (volume = 30ml; insidediameter = 2.5cm), coupled to a plethysm ometer. A standard ionic solution was used to fill the balloon (similar to3 .0 mi) and the communicating vessel system. Calibration experiments (n = 5) displayed a strong (r(2) = 0.99) correlation between graded balloon-volume changes and plethysmometric recordings. Because distending pressure of the stomach remained constant, the balloon-volume recordings were taken as gas tric compliance index. Gastric volume changes, mean arterial pressure, and heart rate of animals of control and experimental groups were monitored for 90 min. The data were analyzed by analysis of variance and the Student-New man-Keuls test. In control animals (n = 5), no significant changes on gastr ic volume and hemodynamic values were found. Experimental animals were trea ted with either yohimbine (n = 5) or bethanechol (n = 5) i.v. injections. T he rats received consecutive doses of yohimbine (0.5 and 1 mg/kg) or bethan echol (1.5 and 3 mug/kg), 30 min apart. Both doses of each treatment transi ently induced hypotension and bradycardia (P < 0.05). Yohimbine treatment(1 mg/kg) increased gastric volume by half(P < 0.05), whereas bethanechol (3 mug/kg) decreased it by 35% (P < 0.05). In summary, this work shows a suita ble method to directly assess gastric compliance in anesthetized rats. (C) 2000 Elsevier Science Inc. All rights reserved.