RIBOFLAVINE 



deficiency and excreted between 50 and 120 /xg. of riboflavine daily. 

 A similar result was obtained by Keys et al. }^ who maintained a number 

 of young men on a diet containing 0-31 mg. of riboflavine per loco 

 cals., that is, between 078 and 0-93 mg. per day. They reported 

 that 12 % of the intake, that is 94 to 112 /xg., was excreted daily, and 

 that approximately the same proportion of a i-mg. test dose was 

 recovered. 



Subjects maintained on a synthetic diet and a natural diet which 

 supplied 1-09 and 1-33 mg. respectively of riboflavine daily excreted 

 152 to 165 and 174 to 229 jug. per day respectively. The one-hour 

 fasting urinary excretion ranged from 37 to 10-9 /xg.^i A mmiber of 

 women who received a daily intake of 079, 1-04, 1-26, 1-62, 2-23 and 

 272 mg. of riboflavine excreted 70, 160, 130, 320, 11 80 and 1310 /xg. 

 daily. Following a 3-mg. test dose, 22, 30, 27, 31, 55 and 56 % 

 respectively was excreted in the following twenty-four hours. ^^ The 

 response to a test dose, like the daily riboflavine excretion, varied 

 inversely with the nitrogen balance. ^^ 



From the above evidence, therefore, it would appear that an 

 adequate intake of riboflavine results in the excretion in the urine of 

 not less than about 200 /xg. per day and in the elimination of not less 

 than 20 % of a test dose within twenty-four hours. 



An observation which does not appear to have been adequately 

 explained was made by B. Sure and Z. W. Ford,^^ who found that 

 when rats, maintained on a synthetic diet supplemented by five pure 

 vitamins, were given subcutaneous injections of thjnroxine (0-5 to 

 I mg. daily), the rate of excretion of riboflavine, though not of aneurine, 

 was greatly increased. At the same time, a large loss of bod5rweight 

 was produced and a large loss of riboflavine from many of the organs . 



Faecal Excretion 



The faecal excretion of riboflavine varied considerably in different 

 individuals, but was less dependent than the urinary excretion on 

 changes in the riboflavine content of the diet, being in fact remarkably 

 constant in any one individual ^^ (see page 185). Unlike the urinary 

 excretion, the faecal excretion bore no relationship to the nitrogen 

 balance. ^2 



Riboflavine in other Body Fluids and Tissues 



The hourly excretion of riboflavine in the sweat was 10 /Ltg., and 

 this value was not increased on administration of riboflavine. ^^ 



Injection of riboflavine into the blood stream caused an immediate 

 increase in the concentration in the liver ; ^^ and this was also increased 



180 



