Difficulties in the Use of Brachycardia Method of Assaying Vitamin B 1

Abstract

Using the brachycardia method as described by Harris and Leong, 1 we have attempted to assay vitamin B₁ hydrochloride (Merck),∗ and the international standard of vitamin B₁. Young piebald rats from our own rat colony, when 45 to 50 gm. in weight, were put on a vitamin B₁-free diet made up of crude casein 18%, McCollum's Salt Mixture (No. 51) 4.5%, sugar 61.5%, cod liver oil 1%, and autoclaved yeast 15%. The latter was strongly alkalinized, autoclaved at 15 lb. pressure in thin layers for 5 hours, and then neutralized and ground. The rats were all kept in wire cages, having meshes 5/8 in. square, in order to prevent possible coprophagy. After about 12 days on the diet, the rats were weighed daily. When the body weights were constant, electrocardiograph records, using a standard Cambridge electrocardiograph, were taken each day. When the heart rate came down to 370 to 390 per minute, the rat was given a single dose of vitamin B₁. A solution of the vitamin Bi hydrochloride was made up daily in distilled water, and the international standard was weighed dry. The dose was mixed with a little autoclaved yeast and then fed to the rat. At least 5 rats received each dose, and they usually ate it within one to 1½ hours. If they took longer than 4 hours, the results were often unsatisfactory. Daily electrocardiograms were taken on each rat at about the same time each morning. The rats were held gently by hand while the records were being made and very rarely struggled or squealed during the process. Great care was taken not to hold the skin tightly, and there was no possibility of asphyxia complicating the results.