Riboflavin and a Further Growth Essential in the Tissues

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Abstract
The primary purpose of this work was to determine the relative concentration, in the chief tissues of a presumably representative omnivorous mammal, of the nutritional factor which has been successively known as vitamin G, lactoflavin and riboflavin. The tissues fed in the main series of experiments were from rats which had been reared on the same diet as in the case of previous studies of distribution of vitamin A. With riboflavin as with vitamin A the concentration in the liver was higher than in the skeletal muscle, and the concentrations in heart and kidney were intermediate; but the distribution of riboflavin shows a much less pronounced quantitative difference than was found in the case of vitamin A; for of vitamin A the concentration was 200 to 400 times as high in the liver as in the muscle, while of riboflavin the concentration in the liver was only ten to twenty times as high as in the skeletal muscles of the same animals. So far as may be judged from smaller numbers of measurements, the concentration of riboflavin was about tenfold higher in kidney, fivefold higher in heart, two- to threefold higher in brain and in spleen, than in skeletal muscle of the same well-nourished animals. The level of dietary intake of riboflavin is found to influence the concentration of riboflavin in the body tissues generally. In neither type of experiment were the differences great enough to indicate any such large storage capacity for riboflavin as the body possesses for storing vitamin A in its liver. The bearing of these findings (and of others reported in the text) upon current concepts regarding the numbers and functions of the nutritionally essential factors of the vitamin B complex are discussed.