The effect of vitamin B12 on rat growth and fat infiltration of the liver.

It has been demonstrated in this laboratory that rats which cease growing on a synthetic “labile methyl”-free diet containing homocystine will resume growth if both folic acid and vitamin Blz are added simultaneously to the diet (1, 2). The growth indicates the synthesis of methionine from homocystine by the rat. It was also found that Lederle concentrated solution of liver extract, in the presence of folic acid, will induce growth in these rats in proportion to its vitamin Blz content. The liver extract is a purified antianemia preparation with a high vitamin Blz assay. In previous experiments, addition of less refined liver extracts to the “labile methyl”-free diet also enabled our rats to utilize homocystine for growth (3). It would seem, therefore, that vitamin Blz was the active factor in these earlier preparations as well. The present experiments were undertaken in an attempt to find out whether vitamin B,z is the sole factor, in the various liver preparations, which is responsible for the growth of our rats on the “labile methyl”-free homocystine diet. To test this possibility, it was planned to feed to rats several different liver preparations and an animal protein factor in doses containing equivalent amounts of vitamin Blz. The vitamin Blz content of the various preparations was determined by microbiological assay. One control group was to be given equivalent doses of crystalline vitamin Blz and another was to receive no vitamin B,z. By correlation of the growth data and determinations of liver lipide we hoped to ascertain whether or not as yet unidentified factors are present in these preparations which could supplement the growth effect due to crystalline vitamin Blz. In addition, we wished to compare the effect of feeding various vitamin B,z preparations on the growth rate and liver lipide content of rats main-