HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS REGISTER		Author Keyword(s) Vol Page [Advanced]

This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this link to a friend Similar articles in this journal Similar articles in PubMed Add article to my folders Download to citation manager Request Permissions Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Jørgensen, J R Articles by Fleming, S E Search for Related Content PubMed PubMed Citation Articles by Jørgensen, J R Articles by Fleming, S E

Absorption and metabolism of octanoate by the rat colon in vivo: concentration dependency and influence of alternative fuels

¹ Department of Medicine CA 2121, Section of Gastroenterology, Copenhagen University Hospital, Rigshospital, Copenhagen, Denmark
² Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California, USA

Correspondence to:
Correspondence to:
S E Fleming, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720-3104, USA;
fleming{at}nature.berkeley.edu

ABSTRACT
Background: Compared with short and long chain fatty acids, medium chain fatty acids (MCFAs) have been shown to provide the highest colonic absorption of substrate carbon. Moreover, colonic epithelial cells fulfil their basic energy requirements as easily from MCFAs as from short chain fatty acids.

Aims: To further characterise octanoate as a colonic luminal substrate, we determined in vivo the influence of (i) substrate concentration and (ii) alternative luminal fuels, on rat colonic transport and metabolism.

Methods: Segments of rat proximal colon (8 cm) were cannulated and perfused for 100 min with ¹⁴C labelled octanoate. The right colic vein was also cannulated and venous blood analysed for total ¹⁴C, ¹⁴CO₂, and metabolites by scintillation counting and high performance liquid chromatography.

Results: Tracer appearance in mesenteric blood stabilised after 20–40 minutes of perfusion. Increasing luminal octanoate concentrations from 2 to 40 mM resulted in linear increases in total carbon absorption. Maximum CO₂ production was reached near 10 mM. A substantial proportion of octanoate was absorbed without being metabolised (59–94%). The luminal presence of a mixture of alternative fuels had no influence on either octanoate transport or metabolism.

Conclusions: This study demonstrated substantial concentration dependent colonic absorption of octanoate, rendering this MCFA a potential and much needed high energy substrate for patients with compromised small bowel function. Moreover, octanoate meets the basic energy requirements of colonic epithelial cells in vivo as well as butyrate. This study also demonstrates the divergence of in vitro and in vivo data regarding fatty acid absorption and metabolism in the colonic epithelium.

Keywords: energy; fat; medium chain triacylglycerol; medium chain fatty acids; short bowel syndrome; small bowel malabsorption

Abbreviations: acyl-CoA, acyl-Coenzyme A; HPLC, high pressure liquid chromatography; K_m, the Michaelis-Menten constant; MCFAs, medium chain fatty acids; LCT, long chain triacylglycerol; MCT, medium chain triacylglycerol; SCFAs, short chain fatty acids; V_max, maximum reaction rate