INTESTINAL SYNTHESIS 



Rats could not be rendered deficient in nicotinic acid by feeding 

 sulphaguanidine when the diet contained tryptophan/^ but the 

 synthesis of nicotinic acid by the intestinal flora in rats was demon- 

 strated in other ways. Thus, on a protein-free diet providing only 

 7 fig. of nicotinic acid per day, rats excreted 25 to 75 /xg. per day in 

 the urine and 40 to 90 /xg. per day in the faeces. The urinary, but not 

 the faecal, excretion was increased by adding casein, axnino acids or 

 choline to the diet. When nicotinic acid was added, 62 % of the 

 additional amount was excreted in the urine and only a negligible 

 proportion in the faeces. ^^ 



Again, Krehl et al.^^ showed that nicotinic acid deficiency induced 

 in rats by the addition of corn or corn grits to the diet, could be cor- 

 rected by feeding carbohydrates that favoured the development of a 

 satisfactory intestinal flora, as well as by feeding tryptophan or 

 materials rich in tryptophan (page 242). Glucose, dextrin and lactose 

 counteracted the growth-depressant effect of maize, but sucrose was 

 without effect. 



The peculiar effect of maize in reducing the growth rate of rats 

 maintained on a low protein diet is due primarily to its low tryptophan 

 content (page 240), but Krehl et al}^ suggested that it was also due in 

 part to amino acid imbalance. They therefore investigated the 

 growth-suppressing effects of other proteins and amino acids, and 

 found 1^ that the addition of glycine or acid-hydrolysed casein sup- 

 pressed the growth of rats receiving a casein-sucrose diet free from 

 nicotinic acid. The growth-suppressing effect of glycine was not 

 observed when dextrin was used as carbohydrate. Although evidence 

 for the mechanism of this effect is lacking, it is suggested that free 

 dietary amino acids may affect the type, quantity or location of intes- 

 tinal micro-organisms and therefore the amount of nicotinic acid 

 synthesised and its availability to the host. 



Rabbits lost weight when fed a nicotinic acid-deficient diet, although 

 large amounts of nicotinic acid were synthesised in the digestive 

 tract, and excreted partly in the faeces, partly in the urine. ^^ 



References to Section 11 



1. P. Ellinger, R. A. Coulson and R. Benesch, Nature, 1944, 154, 



270. 



2. P. Ellinger, R. Benesch and W. W. Kay, Lancet, 1945, 1, 432. 



3. R. Benesch, ihid., 718. 



4. P. Ellinger and A. Emmanuelowa, ibid., 1946, 2, 716. 



5. A. P. Briggs, S. A. Singal and V. P. Sydenstricker, /. Nutrition, 



1945, 29, 331. 



6. C. W. Denko, W. E. Grundy, J. W. Porter, G. H. Berryman, T. E. 



Friedemann and J. B. Youmans, Arch, Biochem., 1946, 10, 33. 



271 



