Bradycardia in thiamin deficiency and the role of glyoxylate.

1. Method of recording the heart rate in rats is described. 2. It was found that during the course of developing thiamin deficiency, the heart rate of rats dropped from 448 to 220 beats/min. (There was no difference between male and female rats.) 3. A number of metabolic products were injected into the normal rats and only glyoxylate was shown to cause a significant drop in heart rate. 4. Graded amounts of Na-glyoxylate were injected peritoneally into the normal rats and blood samples were taken at intervals to test the amount of glyoxylate present. It was found that peak concentration appeared 6 min after injection and thereafter declined or disappeared, depending on the amount of glyoxylate administered. 5. It was found that glyoxylate accumulates in the body of thiamin-deficient rats and in the pair-fed rats reared on restricted diet for a long period. 6. Drop in heart rate depended on the appearance of glyoxylic acid present in the blood rather than on the reduction of body weight.