13C-Acetic Acid Is More Sensitive Than 13C-Octanoic Acid for Evaluating Gastric Emptying of Liquid Enteral Nutrient Formula by Breath Test in Conscious Rats

Breath test using 13C-labeled compound has been used as a convenient method to evaluate gastric emptying. 13C-Labeled acetic acid or octanoic acid has been used in clinic. However, there is few report comparing two compounds. This study aimed to compare 13C-acetic acid and 13C-octanoic acid in newly-constituted breath test for monitoring gastric emptying in conscious rats. After fasting, rats were orally administered Racol (liquid enteral nutrient formula) containing 13C-labeled compound (same molar of 13C-acetic acid or 13C-octanoic acid) and housed in a chamber. The expired air in the chamber was collected in a breath-sampling bag using a tube and aspiration pump. The level of 13CO2 in the expired air was measured using an infrared spectrometer at appropriate intervals for 120 min. Expired 13CO2 air from 13C-acetic acid changed at significantly higher levels than that from 13C-octanoic acid. Cmax and AUC120 min values of expired 13CO2 from 13C-acetic acid were significantly higher than those from 13C-octanoic acid, but Tmax was not different between them. These results show that 13C-acetic acid is more sensitive for monitoring gastric emptying than 13C-octanoic acid in liquid test meal although both acids clearly monitored gastric emptying.