[Experimental and clinical studies on ribosephosphate isomerase (author's transl)]

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.