RIBOFLAVINE 



cellulose, lactose or lard.* Ribofla vine-deficient rats survived for a 

 shorter time when fed on a high fat diet than on a high carbohydrate 

 diet, and they developed a severe spastic paralysis of the hind quarters 

 not observed in rats fed the high carbohydrate diet. Intestinal 

 synthesis was also stimulated by feeding dried liver or a vitamin con- 

 centrate prepared from liver, ^ and animals given this supplement 

 excreted more riboflavine both in the urine and in the faeces. Simi- 

 larly, rats fed on fresh or dried milk excreted more riboflavine in the 

 urine and faeces than did rats fed the same amount of riboflavine in 

 the pure state. The larger faecal excretions were considerably 

 reduced when succinyl sulphathiazole was added to the diet.^ On 

 the other hand, the riboflavine content of liver and muscle tissue was 

 not affected when sulphonamide was added to the diet,'' suggesting 

 that the riboflavine reserves were not dependent to any appreciable 

 extent on the vitamin produced by intestinal synthesis. 



There is some evidence, however, that part of the riboflavine 

 originating in this way may be utilised by animals, for caecectomised 

 rats previously fed on sucrose showed an increased growth rate and in- 

 creased riboflavine excretion when this was replaced by lactose, which 

 favoured bacterial synthesis in the intestine.^ The caecum in rats 

 was presumably an important site of bacterial synthesis, since 

 normal rats synthesised more riboflavine than caecectomised rats 

 when lactose was the carbohydrate supplied ; with sucrose, how- 

 ever, there was little difference between normal and caecectomised 

 rats. 



The phenomenon of refection has already been discussed (see 

 page 75). Refected rats were found to be particularly useful for 

 testing the effect of sulphonamides on the intestinal flora of rats. 

 Addition of several sulphonamides to such animals reduced the amount 

 of riboflavine excreted ; this was restored to normal by administration 

 of ^-aminobenzoic acid.^ 



The first report of intestinal synthesis in humans was made by 

 Najjar et al}^ Twelve young men were maintained on a diet that 

 provided 60 to 90 ju,g. of riboflavine per day. They remained perfectly 

 healthy, without any signs of ariboflavinosis throughout the twelve- 

 week period of the experiment. After a preliminary fall, the urinary 

 excretion remained constant at 150 to 250 /xg. per day, that is, at 

 about twice the intake, whilst the faecal excretion amounted to 200 

 to 600 /xg. per day, that is, up to six times the dietary intake. The 

 ability of the large intestine to absorb riboflavine was demonstrated 

 by giving a retention enema. An attempt to inhibit bacterial syn- 

 thesis of riboflavine by administration of succinyl sulphathiazole for 

 four weeks was, rather surprisingly, unsuccessful. Partial confirma- 

 tion of these results was obtained by M. L. Hathaway and D. E. Lobb,^^ 



184 



