Vitamin B 1 and Thyroxin. ∗

Sure and Smith 1 reported on the protective action of vitamin B against the toxicity of thyroxin administered subcutaneously or orally to the albino rat.

In this investigation attempts were made to balance quantitatively the toxic influence of thyroxin given orally to the rat with a much more concentrated vitamin B₁ extract; also with Williams' crystalline vitamin B₁ (manufactured by Merck).

The vitamin B₁ concentrate was furnished by the Eli Lilly Research Laboratories and is a product that is being tested clinically. This preparation is indicated for parenteral use, each cc. containing 150 Sherman units of vitamin B₁.

Seventy sets of animals in groups of 4 were used for this study, which were litter mates of the same sex. In each set, animal A received a diet deficient only in vitamin B₁, which represented the negative control; animal B received the diet of animal A, and in addition a daily dose of thyroxin; animal C received the same diet, a daily dose of thyroxin, and a daily dose of either the Lilly concentrate or crystalline vitamin B₁; animal D received the same diet, a daily dose of either source of vitamin B₁, but no thyroxin, which represented the positive control. The thyroxin was given daily in doses ranging from 0.05 mg. to 0.2 mg. The Lilly vitamin B₁ concentrate was furnished in doses supplying 1.5 to 30 Sherman units daily. The crystalline vitamin B₁ was administered daily in amounts ranging from 1γ to 300γ or 0.001 mg. to 0.3 mg.

The criterion of complete protection against thyroxin poisoning was not only the ability of the animal to survive but also to make as good a growth as if thyroxin were not introduced as a supplement to the experimental diet. 2