Absorption of short-chain fatty acids from the human ileum

Acetate, propionate, andn-butyrate are the major short-chain fatty acid (SCFA) anions in the gastrointestinal tract of animal and man, accounting for 90% of total SCFA in stool water. Their absorption from the human ileum was investigated in 8 volunteer subjects by the triple-lumen perfusion technique. Each test solution contained one of the SCFAs at a concentration of 0–100 mM; sodium, potassium, and bicarbonate concentrations were kept constant, as were pH and osmolality. Absorption of each SCFA was found to be rate-limited with an apparentK_m between 22 and 27 mM and a calculatedV_max between 0.54 and 0.82 mmol/hr cm. Water, sodium, and chloride transport were not affected by substantial rates of SCFA absorption. Rather, significant stimulation of calculated bicarbonate secretion and a rise in intraluminal pH were consistently observed. The results are compatible with either of two mechanisms for SCFA absorption: an anion exchange between bicarbonate (or hydroxyl) and SCFA ions, or protonation of the SCFA anion at the mucosal surface followed by simple diffusion of nonionized SCFA into the absorbing cell.This work was supported, in part, by a grant (RR-58) from the General Clinical Research Center Program of the Division of Research Resources and by a research grant (AM-12985-05) from the National Institutes of Arthritis, Metabolic and Digestive Diseases, National Institutes of Health, Bethesda, Maryland.Presented, in part, at the Annual Meeting, Central Society for Clinical Research, November 6, 1976, Chicago, Illinois.Dr. Schmitt was supported by a Special Post Doctoral Research Fellowship Award (5-F03-AM53883) from the National Institute of Arthritis, Metabolic and Digestive Diseases, National Institutes of Health, Bethesda, Maryland.