Objective: To investigate the possible use of a (13)C-uracil breath test for gastric emptying by evaluating the pharmacokinetic properties of (13)C-uracil in a breath test in rats, in comparison with (13)C-acetate and (13)C-octanoate, traditional (13)C-probes for gastric emptying.
Material and methods: Absorption of the (13)C-probes from different parts of the gastrointestinal tract was evaluated in fasted rats. (13)C-Uracil breath tests for gastric emptying were carried out in conditions where delayed gastric emptying was induced by clonidine, quinpirole, and propantheline, and in a postoperative ileus model. Following oral administration, we measured residual (13)C-uracil in the stomach and correlated the amount with the breath response.
Results: All the (13)C-probes employed were well absorbed from the intestine after intraduodenal administration. After intragastric administration, (13)C-uracil was not absorbed from the stomach, but (13)C-acetate and (13)C-octanoate were partly absorbed from the stomach. The cumulative (14)C-uracil recovery (%) at 168 h was 92.3, 6.3, or 0.5%, from expired gases, urine, and feces, respectively. Delta(13)C values in (13)C-uracil breath tests were decreased in conditions characterized by delayed gastric emptying. A highly negative correlation was observed between the breath response and the residual ratio of (13)C-uracil in the stomach after oral administration of (13)C-uracil, indicating that (13)C-uracil can be used as an in vivo probe for evaluating gastric emptying in a quantitative manner.
Conclusions: This study showed that (13)C-uracil has desirable pharmacokinetic properties as an in vivo probe of gastric emptying. It is thus suggested that the (13)C-uracil breath test may be useful for the measurement of gastric emptying in humans.