Simple and noninvasive breath test using 13C-acetic acid to evaluate gastric emptying in conscious rats and its validation by metoclopramide

The C-13-breath test has been used to clinically evaluate gastric emptying. However, this method has not been sufficiently validated in experimental animals. The present study aimed to establish a simple and noninvasive C-13-breath-test system in Sprague-Dawley male rats. After fasting, rats were orally administered Racol containing C-13-acetic acid and housed in a desiccator. The expired air in the chamber was collected in a breath-sampling bag using a tube and aspiration pump. The level of (CO2)-C-13 in the expired air was measured using an infrared spectrometer at appropriate intervals for 120 min. During this period, the rate of (CO2)-C-13 excretion increased, peaked, and decreased thereafter. The maximum concentration (C-max) and area under the curve (AUC(120 min)) of (CO2)-C-13 excretion increased in volume- and dose-dependent manners. The time taken to reach the maximum concentration (T-max) of (CO2)-C-13 excretion increased as the volume increased, but was not affected by the dose of C-13-labeled acetic acid, Metoclopramide dose-dependently increased the C-max and shortened T-max of (CO2)-C-13 excretion compared with those of the control rats, whereas the AUC(120 min) was not affected. These results confirm that this simple method can successfully evaluate gastric emptying. Moreover, this system is suitable for investigating additional physiological functions using other labeled compounds.