The Bacterial Synthesis of Nicotinic Acid in Animals

Numerous workers (72, 74, 75) have reported that the rat can thrive well on a black tongue producing diet. Balance studies (76) showed that rats excreted as much as 40 y of nicotinic acid in excess of the intake. The fecal output alone was three times the intake, a strong evidence for intestinal synthesis which has been shown to occur in the cecum (77). It has also bpen claimed to take place in the tissue of the rat (78). Ruminants (79) also thrive well for a long period on a ration deficient in nicotinic acid with no ill effects. In sheep the excretion of nicotinic acid (80, 81) remains substantial despite a deficient intake and the nicotinic acid level in the blood (81) is comparable in value to that of animals fed a stock ration. A study of the rumen of the calf (51, 52) showed clearly that nicotinic acid is synthesized to a considerable extent. Similar results were obtained in the cow (76). 

Although there is little doubt that nicotinic acid synthesis takes place in the rat, sheep, cow, and other animals, the simple measurement of nicotinic acid excretion does not seem to be an adequate index. From ail available evidence the only index of nicotinic acid deficiency appears to be the urinary F2 fraction of Najjar and Wood (82-86). This was confirmed by workers using the Fj assay (87, 88) and the so-called trigonelline fraction (89, 90) which is mainly, if not all, F2 (91, 92). The F2 fraction, a derivative of V -methylnicotinamide (80, 91, 93-95) was found to be excreted in substantial quantities in rats and pigs while on a nicotinic-acid-deficient diet, a fact which indicates synthesis of the vitamin. 

Numerous bacteria have been found to synthesize nicotinic acid in pure media. E. colt, B, aerogenes, A. fecalis, B. vulgalus, B, mesentericus (60), Aerobacter aerogenes, Pseudomonas fiuorescens, Proteus vulgaris, and Clostridium butylicum (65). 

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