PYRIMIDINE METABOLISM IN NORMAL MAN STUDIED WITH N15LABELED URACIL

Abstract

IN CONTRAST to our knowledge of purine metabolism, which is fairly well understood, our knowledge of pyrimidine metabolism in man is rather limited. The pyrimidines, as well as the purines, are components of such physiologically important substances as nucleic acids, yet the intermediary stages of pyrimidine metabolism have not been established, and the final end-product or products of degradation in man are not known with any degree of certainty. Some of the earliest work on pyrimidines dates back to about 1901, when Steudel fed several of them to dogs and concluded that they did not contribute to purine metabolism and were not excreted as the intact molecule but were degraded (1, 2, 3). In 1907 Sweet and Levine fed thymine to a dog with an Eck fistula and recovered half in the urine (4). When the same amount was fed in the form of nucleic acid, none could be found in the urine. In 1910 Mendel and Myers concluded that pyrimidines did not become purines, did not metabolize to urea to any degree, and could be recovered in the urine of man when fed (5). When nucleic acid-rich diets were given, pyrimidines were not found in the urine. Wilson recovered pyrimidines quantitatively from the urine of rabbits, but did not find any in the urine of a man given uracil nucleoside.