Gastric functions such as adaptive relaxation have usually been monitored in rats using a surgically inserted barostat’s balloon. However, surgery causes physiological damage to the rat stomach. This study is an investigation of adaptive relaxation of the rat stomach using a slightly modified balloon, which is introduced into the stomach through the mouth of anesthetized rats without the need for balloon surgery, attached to a brostat. In this case, the balloon was placed between the fore-stomach and the fundus, but towards the fore-stomach. The balloon volume increased gradually just after an increment in the balloon pressure, and reached a plateau within 1 min. This increased volume just after the increment of the balloon pressure was defined as adaptive relaxation. Adaptive relaxation increased with pressure increases in a pressure dependent manner. Pre-treatment with Nω-nitro-L-arginine methylester (30 mg/kg, i.v.) caused this adaptive relaxation to be significantly inhibited as compared with the control. On the contrary, adaptive relaxation was significantly enhanced by pre-treatment with capsaicin (0.5 mg/kg, p.o.). These findings show that this method is both useful for investigating the physiology of adaptive relaxation of the stomach without surgery and to show that nitric oxide plays an important role in the adaptive relaxation of the stomach as reported previously.
This study reports a method for the evaluation of both gastric emptying and gastrocecal transit times in rats simultaneously by using the same breath testing system measuring equipment. Male rats were used after fasting. Gastric emptying and gastrocecal transit time were evaluated by using [1-13C] acetic acid (8 mg/kg) and lactose-[13C] ureide (60 mg/kg), respectively. A mixture of both 13C-labelled compounds dissolved in Racol (liquid nutrient formula) was administered orally. The level of 13CO2 in the expired air was measured using an infrared spectrometer at appropriate intervals for a period of 420 min. The level of 13CO2 in the expired air from [1-13C] acetic acid increased with time and peaked at about 30 min before decreasing, while that from lactose-[13C] ureide increased after about 180 min. The time taken to reach the maximum value of gastric emptying (Tmax) was 27.5 ± 0.9 min. Gastrocecal transit time was 180 ± 11.5 min, which was calculated as the time before the 13CO2 value increased again. These results accorded with the results of gastric emptying and gastrocecal transit time evaluated by using each 13C-labelled compound separately. These results demonstrate that this method is useful for the simultaneous evaluation of gastric emptying and gastrocecal transit times in rats.