Bradycardia in the vitamin B1-deficient rat and its use in vitamin B1 determinations

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Abstract
The estimation of vitamin B1 by the heart rate method (see Biological Abstracts Volume 8 (2) : Entry 3623), which consists in daily measurements of the effect on heart rate of single doses of the unknown fed to rats suffering from vitamin B1 deficiency, was checked by tests on 4 substances: activated acid clay standard, dried yeast, marmite, and wheat germ, by several independent methods. The new methods were: (a) curative tests on polyneuritic convulsions in rats, which give close agreement between animals receiving duplicate doses; (b) a growth rate method by which, under accurately defined conditions, differences of [plus or minus] 20% are readily detected, and in 3 out of 5 animals [plus or minus] 15%; the final results reached by the 3 rat methods appeared to agree within [plus or minus] 5%. The comparative values found, activated clay standard as 100, were: yeast 18.8, 19.3, 20, 18; marmite 8.3, 8.7, 9.1, 8.5; wheat germ 7, 6.9, 7.2, by the bradycardia, convulsions, growth-rate and pigeon (head retraction) methods respectively. The heart rate method is convenient, rapid, simple, and economical, and it can be used for foodstuffs containing smaller amounts of vitamin B1 than can be determined by the other methods, e.g., white and brown breads and other wheat products growth tests on which are vitiated by the occurrence of refection. A rat dying from acute avitaminosis has a very low heart rate (300 per min.) and no polyneuritic convulsions. A rat given slight traces of vitamin B1 and developing chronic hypovitaminosis has a less severe bradycardia (400 per min.) but convulsions. The traces of vitamin B1 may keep the heart rate at a high enough level to enable the animal to survive and so permit the chronic symptoms to develop. An earlier suggestion is confirmed, that the bradycardia is correlated with the accumulation of lactic acid in the vitamin B1-deficient animal. Vitamin B1 appears to have the property of a coenzyme-like substance intervening in the chain of carbohydrate oxidation reactions.