Transfer of Purines from Liver to Erythrocytes

Abstract

Since erythrocytes cannot synthesize purines de novo, but act as carriers of purines from the liver to other tissues, purine transport from the liver to erythrocytes was examined by measuring in vivo incorporation of ¹⁴C-glycine into purine bases in the liver and levels of ¹⁴C-purines in erythrocytes of normal and partially hepatectomized (treated) rats. It was found that glycine incorporation into purines was stimulated in regenerating liver and that the ratio of radioactivity in guanine compounds to that in adenine compounds was 3 times higher in regenerating liver than in normal liver. A similar increase in this ratio was found in the erythrocytes of treated rats. However, in vitro experiments on primary cultured cells showed that the purines released were inosine, hypoxanthine, xanthine, and allantoin, but not adenine or guanine compounds. Normal hepatocytes released some purine, mainly as allantoin, while regenerating liver cells released twice as much, mainly as equal amounts of inosine and allantoin. The plasma concentration of hypoxanthine per liver weight also increased significantly in treated rats. The uptakes of purines by erythrocytes from normal and treated rats were similar and serum from treated rats did not stimulate the uptake. These results suggest that, compared with normal liver, regenerating liver forms more guanine than adenine, and releases more of their metabolites, hypoxanthine, inosine, and xanthine, and that when these products are taken up by erythrocytes they are redistributed into other purines, and especially guanine compounds.