Short-chain fatty acids (SCFAs) that were labeled with 13C were infused into rat ceca to study their absorption and metabolism using an external ileal fstula and a 13C-SCFAs breath test. After fasting overnight, rats were infused intracecally once daily with either 0.2 ml of saline containing 15 μmol of [1-13C] sodium acetate (13C-A)，[1-13C] sodium propionate (13C-P), or [1-13C] sodium n-butyrate (13C-B) via the ileal fstula．The 13C-SCFAs breath test was performed over 120 min．Expired air was collected at appropriate intervals and the concentrations of 13CO2 in the air were measured with an infrared analyzer．Expired 13CO2 increased rapidly after intracecal infusion in all treatment groups and then decreased gradually．Maximum concentrations (Cmax) of 13CO2 in the expired air was signifiantly higher in the 13C-P than in the 13C-A and 13C-B treated groups．The time taken to reach Cmax in the expired air was shorter in the 13C-P group than in the other groups．The Cmax increased in a dose-dependent manner following administration of all SCFAs．Post 13C-SCFA intravenous infusion, no signifiant diferences in Cmax were observed between rats treated with 13C-A and 13C-P．These results suggest that the postabsorptive rate of oxidation of propionate does not difer from that of acetate．Therefore，the differences that appeared in the expired 13CO2 from intracecally-infused 13C-SCFAs may refect diferences in the absorptive steps of these SCFAs from the cecum．
Key words : short chain fatty acids，acetate，propionate，13C-SCFAs breath test，stable isotopes |
