The 13 C-octanoic acid breath test: validation of a new noninvasive method of measuring gastric emptying in rats R. SCHOONJANS, B. VAN VLEM,* N. VAN HEDDEGHEM, W. VANDAMME, R. VANHOLDER,* N. LAMEIRE,* R. LEFEBVRE  & M. DE VOS Gastroenterology Division, Department of Internal Medicine, Ghent University Hospital, B-9000 Ghent, Belgium *Renal Division, Department of Internal Medicine, Ghent University Hospital, B-9000 Ghent, Belgium  Heymans Institute of Pharmacology, Ghent University, B-9000 Ghent Abstract Currently available rat models for measur- ing gastric emptying are hampered by the necessity to kill the animals at the end of each experiment, which makes repetitive testing impossible. We have devel- oped and validated a noninvasive test model, adapted from the 13 C-octanoic breath test in humans, for repetitive measurements of gastric emptying in rats. Male Wistar rats were trained on a fixed protocol to eat a piece of pancake doped with 1 lg 13 C-octanoic acid after 12 h fasting, and to stay thereafter in cylindrical glass cages. Breath tests were performed by a fully automated system of computer-guided switching valves, which collected consecutive breath samples. All breath samples were analysed by gas chromatog- raphy and isotope mass spectrometry. The area under the curve (AUC) from the cumulative 13 CO 2 excretion from 0 to 6h was determined by the trapezium method to calculate the gastric half-emptying times (t½). Inter-day variability was determined. The effect of subcutaneous or intraperitoneal injection of saline was studied. The test was further validated for phar- macological interventions by oral administration of cisapride and parenteral administration of atropine, to induce, respectively. acceleration and delay of gastric emptying. Mean gastric emptying times ± SD of 24 rats were 119.3 ± 28.2 min, 138.7 ± 26.0 min, and 124.5 ± 30.9 min on three different test days. The mean coef- ficient of variation of three repeated measurements in the same 24 rats was 17.5%. No significant differences were observed after subcutaneous or intraperitoneal injection of saline. In a second test series of eight rats, cisapride significantly accelerated gastric emptying (mean t½ 112.7 ± 33.1 min, P < 0.05), while atropine caused a significant delay (mean t½ 205.9 ± 24.9 min, P < 0.05) when compared to control test results (mean t½ 140.7 ± 16.7 min) in the same rats. We validated the 13 C-octanoic breath test to study gastric emptying in rats. This test method obviates the necessity to kill laboratory animals and allows repetitive measure- ments of gastric emptying to study its physiology or pathophysiology as well as the effect of pharmacolo- gical agents. Keywords atropine, cisapride, gastric emptying, rats, stable isotopes. INTRODUCTION Radioscintigraphy is generally accepted as the Ôgold standardÕ for measuring gastric emptying in humans. 1 The 13 C-octanoic breath test has been widely applied in clinical diagnosis of gastric emptying disorders since the first report of this test by Ghoos et al. 2 It is more suitable for repetitive measurements and applications in children because no radioactive substance is used. However, neither of these two test methods has been validated for laboratory animals. Most rat models currently used for measuring gastric emptying are hampered by the necessity to kill the animals at the end of the test, which makes repetitive testing impossible, therefore, these gastric-emptying studies are limited to transversal comparisons of single Address for correspondence R. Schoonjans, Gastroenterology Division, Department of Internal Medicine, University Hospital 1K12 IE, De Pintelaan 185, 9000 Ghent, Belgium. Tel.: + 32 92402371; fax: 32 92404982; e-mail: schoonjans.renaat@yucom.be Received: 5 November 2001 Accepted for publication: 1 March 2002 Neurogastroenterol. Mot. (2002) 14, 287–293 Ó 2002 Blackwell Science Ltd 287