In order to know the clinical significance of serum
ribose-5-phosphate isomerase (RPI), the activity of this
enzyme was determined in sera of normal subjects and patients with hepatic disorders or malignant
tumors. Experimentally, the
enzyme activity in sera and liver tissue was followed in rats with acute hepatic damage induced by
carbon tetrachloride (CCl4) or rats with
hepatoma induced by
3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB). The following results were obtained: 1) Serum RPI activity increased markedly in rats with CCl4-induced liver damage, whereas the activity in liver tissue decreased, both being related with reciprocally. 2) In the early phase of acute
hepatitis, serum RPI activity increased and gradually decreased thereafter. No significant increase was observed in other hepatic disorders. 3) Both serum and liver RPI activity increased in rats with
hepatoma induced by 3'-Me-DAB. 4) An increase in serum RPI activity was seen in higher percentage in
cancer patients. Higher
enzyme activity and its higher incidence were observed in patients with hepatic
metastasis or primary
hepatoma than in patients without
metastasis. From these results it is concluded that serum RPI activity as a diagnostic aid is useful in estimating
clinical course of hepatic disorders and also in diagnosing malignant
tumors, especially in substantiating a diagnosis of
metastasis to the liver.