Tissue Folacin Stores in Rats Measured by Radioassay

Abstract

Serum and liver folacin levels determined by competitive protein binding assay fell rapidly after the administration of folacin-depleting diets to female rats and returned to normal after dietary repletion with folic acid. Values of liver folacin measured by radioassays were comparable to values concurrently-determined by assay with Lactobacillus casei. Liver, serum, and kidney folacin levels were similar to those previously determined in this laboratory and to published values for total folacin determined by L. casei. Incubation of liver homogenates for 3-5 hr at 37° led to a threefold increase in folacin concentration when measured by L. casei, but did not alter values determined by radioassay.