Short chain fatty acids in rats with jejunal blind loops. I. Analysis of SCFA in small intestine, cecum, feces, and plasma.

The luminal and plasma levels of short chain fatty acids (SCFA), products of bacterial fermentation, were measured in rats with surgically produced, self-filling blind loops located in the proximal small intestine. High levels of acetic, propionic, and butyric acids were detected in the blind loop segment and in the distal small bowel, regions which in normal and sham-operated rats contain no SCFA. Isobutyric, isovaleric, and valeric acids were also present. Feeding or fasting made little difference in the amount or composition of luminal SCFA. Although the amount of SCFA in each animal varied, the ratio of these acids was relatively constant. The ceca of the blind loop rats had relatively less acetic acid (48% of total SCFA) than did normal rats (64%) and proportionately more isobutryic, isovaleric, and valeric acids. The concentrations of SCFA increased in the feces of blind loop rats. The acetic acid concentration was 50% higher in blind loop rat feces; propionic, isobutryic, and isovaleric acids were elevated to a greater extent. The total output of most of the SCFA was also of acetic acid (137 +/- 32 mug per ml), the rest being isovaleric (5.2 +/- 2.6 mug per ml) and isobutyric (1.4 +/- 0.7 mug per ml) acids. Blind loop animals had nearly twice the concentration of acetic acid in the plasma (240 +/- 29 mug per ml) as normal animals, while the other acids were unchanged. The present study suggests that endogenous substances may be important substrates for the production of SCFA in the intestinal lumen. The high levels of SCFA in the small intestine and in feces and the substantial increase in the concentration of acetic acid in thvergrowth syndrome if the same relationships were found in man.