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)
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