In vivo absorption of medium-chain fatty acids by the rat colon exceeds that of short-chain fatty acids.
OBJECTIVE
Short-chain fatty acids (SCFAs) are main fuels of the colonic epithelium, and are avidly absorbed by the colon of animal and man. The current knowledge on colonic metabolism and absorption of medium-chain fatty acids (MCFAs) is limited. In some clinical situations, colonic absorption of high-energy substances could compensate for reduced absorptive capacity because of a shortened or malfunctioning small bowel. We evaluated and compared colonic absorption and metabolism of MCFAs (octanoate, decanoate, and dodecanoate), SCFAs (acetate and butyrate), and long-chain fatty acids (LCFAs) (oleate).


METHODS
Rats were surgically operated on to cannulate a 7-cm segment of proximal colon, isolate the vasculature, and cannulate the right colic vein draining this segment. The lumen was perfused with (14)C-labeled substrates for 100 minutes. Right colic vein blood was analyzed for total (14)C, (14)CO(2), and metabolites by scintillation counting and high-performance liquid chromatography.


RESULTS
The transport from the colonic lumen to mesenteric blood of substrate carbon from MCFAs exceeded by 2-13-fold that of SCFAs and LCFAs. The CO(2) production from the oxidation of MCFAs was as high as or higher than that from SCFAs. CO(2) produced from the LCFA, oleate, was lower than from SCFAs or MCFAs. In addition to CO(2), ketone bodies were major metabolites of SCFAs and MCFAs. Ketogenesis from butyrate and the MCFAs was significantly higher than from acetate and oleate. A substantial proportion (50%-90%) of all substrates was absorbed without being metabolized.


CONCLUSIONS
The colonic epithelium serves to absorb and partially metabolize MCFAs. For patients with a compromised small-bowel function, colonic absorption of MCFAs could represent an important way of receiving calories.
Jørgensen
J R
JR
Department of Medicine, Section of Gastroenterology, Copenhagen University Hospital, The Rigshospital, Copenhagen, Denmark.
Fitch
M D
MD
Mortensen
P B
PB
Fleming
S E
SE
D000818:Animals; D002244:Carbon / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid; D003106:Colon / Q000098:blood supply / Q000378:metabolism*; D005227:Fatty Acids / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D007408:Intestinal Absorption / Q000502:physiology*; D007421:Intestine, Small / Q000098:blood supply / Q000378:metabolism; D007657:Ketone Bodies / Q000378:metabolism; D008297:Male; D008638:Mesenteric Arteries / Q000378:metabolism; D008970:Molecular Weight; D010477:Perfusion / Q000592:standards; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results
D005227:Fatty Acids; D007657:Ketone Bodies; D002244:Carbon