SHORT-CHAIN FATTY-ACID ABSORPTION FROM THE HUMAN DISTAL COLON - INTERACTIONS BETWEEN ACETATE, PROPIONATE AND CALCIUM

Objective: Our purpose was to conduct a preliminary study to see if propionate and calcium affected acetate absorption, and acetate and calcium affected propionate absorption from the human distal colon. Methodology: We studied six healthy subjects on eight occasions in randomized order after overnight fasts. Test solutions (300 ml) were infused into the rectum, retained for 30 minutes, and then the infusion fluid was collected for analysis. The infusion solutions contained combinations of sodium acetate (56.25 mmol/L), sodium propionate (18.75 mmol/L) and calcium chloride (50 mmol/L) plus polyethylene glycol (PEG) as an unabsorbable marker. Results: The reduction in the acetate:PEG concentration ratio over 30 minutes after acetate alone, 4.1 +/- 4.2, was significantly less than after acetate plus propionate, 40.2 +/- 11.9, and acetate plus calcium, 34.0 +/- 8.9 (p < 0.05). However, the change in acetate:PEG ratio when acetate, propionate and calcium were all infused together, 13.2 +/- 4.6, was no different from acetate alone. The reduction in the propionate:PEG concentration ratio after propionate alone was 15.7 +/- 3.3, and this was not significantly affected by adding acetate and calcium either alone or together. Conclusions: We conclude that the absorption of acetate in the rectum and distal colon of humans may be influenced by the presence of calcium and propionate. More detailed kinetic studies are required to confirm these results and characterize the transport mechanisms involved.