Purine synthesis and reutilization in folate-deficient rat hepatocytes

Although folic acid is known to be involved in the pathways of purine metabolism, the precise changes brought about in purine synthesis, reutilization, pool sizes, and ratios by experimental folate deficiency are not clear. Consequently, these aspects of purine metabolism were measured in hepatocytes from control and folate-deficient rats fed an amino acid diet with and without folic acid, respectively. Purine synthesis and reutilization were measured as the rates of incorporation of [U-14C]glycine and [G-3H]hypoxanthine, respectively, into the adenine and guanine pools of freshly isolated hepatocytes after a 3-hour incubation in folate-free, as well as folate- and/or thymidine-supplemented culture media. Hepatocytes from folate-deficient rats had the same rates of purine synthesis as those from control rats. Purine reutilization, purine pool sizes, and the adenine:guanine ratios were lower in hepatocytes from deficient compared with control rats. Purine synthesis was increased when folic acid or thymidine was added to the culture medium. Although hepatocytes from folate-deficient rats had a lower rate of purine reutilization compared with those from control rats, the reutilization rates did not respond to the addition of folic acid or thymidine to the culture medium. The data suggest that purine synthesis was not impaired but purine reutilization was diminished in folate deficiency. Thymidine was as effective as folic acid in stimulating purine synthesis in both control and folate-deficient hepatocytes.