Purine nucleotide catabolism in rat liver - Labelling of uric acid and allantoin after treatment with oxonic acid and allopurinol

In our previous experiments on rat liver we found that 15' after intraperit oneal administration of 1(4C)-formate the specific radioactivity of allanto in was always higher than that of uric acid. The present experiments have b een carried out to interpret this unexpected result, which was only observe d in liver and we studied: a) the incorporation of C-14-glycine into uric a cid and allantoin; b) the effects of two competitive inhibitors of xanthine oxidase and uricase, oxonic acid and allopurinol respectively, on levels o f uric acid and allantoin in liver and on their specific radioactivity afte r administration of labelled precursor. The results suggested: a) that unde r normal conditions, the formation of allantoin is so fast that it exceedes export from liver to serum, and thus the radioactivity of labelled precurs ors accumulates in allantoin; b) that when allopurinol or oxonic acid are a dministered, the rate of export exceeds that of allantoin formation and the incorporation of radioactivity into allantoin is lower; c) that not all th e data, however, could be interpreted on this basis, but seems to require t he existence of different pools of uric acid, which are transformed separat ely into allantoin. (C) 2001 Elsevier Science Inc. All rights reserved.