Fatty acids and intestinal metabolism

Oxidative metabolism of rabbit and rat intestine with short chain fatty acids and glucose: an evaluation of data analysis

1. Glucose sustained VO2 of rabbit ileum, caecum, and distal colon better than SCFAs. 2. In rabbit proximal colon, while VO2 was stimulated in the presence of butyrate it was not sustained. 3. Rat caecum utilized glucose but it was not necessarily the best substrate for either the ileum or colon of this species and SCFAs appeared to stimulate VO2 of rat ileum and inhibit VO2 in rat caecum and colon. 4. It was concluded from the comparison of the two methods of data analyses that curve-fitting the data by a negative exponential equation provides for a more clear and in depth interpretation of such studies.

Metabolic induction of experimental ulcerative colitis by inhibition of fatty acid oxidation

There is some evidence that failure of fatty acid or beta-oxidation in the epithelium of the colonic mucosa is associated with the development of ulcerative colitis. We tested the hypothesis that inhibition of fatty acid oxidation in the colonic mucosa of the rat reproduces the histological, clinical and biochemical lesions of acute ulcerative colitis of man. A specific inhibitor of beta-oxidation, sodium 2-bromo-octanoate, was instilled rectally for 5 days or exposed to isolated colonic epithelial cells which were subsequently tested for their ability to beta-oxidize n-butyrate. Weight loss, bloody diarrhoea and histological lesions occurred with 2-bromo-octanoate treated rats but not control animals. Ketogenesis and 14CO2 production was inhibited by 2-bromo-octanoate. Of 12 animals mucosal ulceration developed in six out of eight surviving animals and in all four animals that died. Ulceration, mucus cell depletion, vessel dilatation and increases of inflammatory cells were the most prominent histological changes. Present observations indicate that inhibition of beta-oxidation produces acute colitis and suggests that inhibition of beta-oxidation is primary rather than secondary in the genesis of ulcerative colitis. A search for agents producing such biochemical lesions in man should be undertaken.

Oxidative phosphorylation accompanying oxidation of short-chain fatty acids by rat-liver mitochondria

1. The factors concerned in the estimation of P/O ratios when fatty acids are oxidized by rat-liver mitochondria have been assessed. 2. The oxidation of butyrate, hexanoate and octanoate is accompanied by ATP synthesis. At low concentrations of the fatty acids, P/O ratios approximately 2.5 are obtained. 3. Oxidative phosphorylation is uncoupled, respiratory control ratios are lowered and respiration is inhibited when the concentration of the fatty acid in the incubating medium is raised (to 5-10mm); octanoate is a more potent uncoupler than either hexanoate or butyrate. 4. Serum albumin and carnitine, either singly or in combination, protect the mitochondria from the effect exerted by the fatty acids. 5. The rate of oxidation of short-chain fatty acids in the presence of ADP is increased in the presence of carnitine.

Transport and metabolism of fatty acids by isolated rumen epithelium

1. The metabolism of even-numbered saturated (acetic acid to stearic acid) and unsaturated (oleic acid and linolenic acid) fatty acids by diaphragms of isolated rumen epithelium has been investigated. 2. When fatty acids are presented to the papillae surface, ketone bodies are released from the opposite (muscle) side of the tissue. 3. When the concentration of octanoate or decanoate is increased to a critical value, which varies inversely with the chain length of the fatty acid, the respiration of the tissue is inhibited and ketone body synthesis is diminished. Under these conditions unmetabolized fatty acid crosses the tissue down a concentration gradient. 4. The inhibitions by octanoate and decanoate are more marked when the fatty acid is presented to both surfaces of the rumen epithelium. 5. During the oxidation of octanoate and decanoate at non-inhibitory concentrations, small quantities of shorter chain fatty acids, including acetate, are produced.

Intestinal metabolism of fatty acids

1. The effect of concentration on the oxidation and incorporation into lipids of lauric acid and linoleic acid by rings of rat small intestine has been studied in vitro. 2. In the absence of glucose, the oxidation of lauric acid in the range 0.01-5.0mm showed a maximum at 0.1mm. In the presence of glucose the maximum was at 0.5mm. The oxidation of linoleic acid in the presence of glucose increased throughout the concentration range 0.01-5.0mm. 3. The incorporation of lauric acid into lipids was maximal at 0.5-0.6mm in the presence of glucose, but at 10mm in the absence of glucose. At 0.8mm-lauric acid, in the presence of glucose, over 75% of the incorporated lauric acid was in triglycerides, but at 10mm they only contained 30%. The incorporation of glucose carbon into glycerides paralleled the incorporation of lauric acid. 4. In the range 0.01-2.5mm-linoleic acid the quantity incorporated into lipids increased. In the range 0.01-0.4mm linoleic acid was incorporated predominantly into triglycerides, but between 0.4 and 1.0mm most was in diglycerides, and between 2.5 and 5.0mm most was in monoglycerides. 5. The relationship of fatty acid concentration to the mechanism of absorption is discussed, together with the correlation between the distribution of the absorbed fatty acids within the tissue lipids and the lipase activity of intestinal mucosa.