1. To test the hypothesis that the colon contributes significantly to venous plasma acetate concentrations, experiments were carried out in healthy volunteers and ileostomy patients.

2. Fasting plasma acetate levels were measured in 10 ileostomy patients and compared with those in 21 control subjects. Values in ileostomy patients (21.3 ± 0.8 μmol/l) were significantly lower than in control subjects (48.0 ± 4.2 μmol/l).

3. Plasma acetate concentration was estimated in eight healthy volunteers during 108 h of continuous fasting. Acetate concentrations rose significantly from 12 h (43.9 ± 4.4 μmol/l) to 108 h of starvation (114.0 ± 15.6 μmol/l) and fell back to normal fasting values on refeeding and another 12 h fast (44.3 ± 4.7 μmol/l).

4. When colonic fermentation was stimulated after oral ingestion of 10 g of lactulose, the plasma acetate concentration increased significantly (from 44.0 ± 7.4 to 114.4 ± 16.2 μmol/l) in seven healthy control subjects. This rise was not affected by concomitant dosage of metronidazole.

5. These data suggest that there are at least two major sources of acetate in man, an endogenous source and the colon which probably becomes more important when fermentation of carbohydrate is occurring.

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