Abstract
Previous experiments 1 indicated that in the metabolism of uracil in the dog we are dealing with the following sequence of reactions: Uracil → Isobarbituric Acid → Isodialuric Acid → Urea + an unknown carbon compound. Offe 2 has shown that formyloxaluric and oxaluric acids are intermediate products in the oxidation of isobarbituric acid in vitro by means of permanganate. Quite recently, Johnson and Flint 3 have found that these compounds are also formed in the course of the oxidation of uracil by ozone.
Formyloxaluric acid and oxaluric acid were fed to dogs maintained in nitrogen equilibrium. In every case there was an increase in the urea output, suggesting that these substances were metabolized. Injection experiments with oxaluric acid yielded the same results. Formyloxaluric acid, on the other hand, when injected, was found to be toxic.
These findings seem to indicate that in the metabolism of uracil in the dog we are dealing with an oxidation resembling that in vitro as follows:
Uracil → Isobarbituric Acid → Oxaluric Acid → Urea + Oxalic Acid.
They also suggest that oxaluric acid might be an intermediate product in purine metabolism. The formation of this substance as an end-product of the oxidation of uric acid by various oxidizing agents is a well-known fact. 4
Experiments were also carried out with alloxan and parabanic acid to determine whether these substances might be intermediary products of purine breakdown in the animal body. Parabanic acid, when fed to dogs in nitrogen equilibrium, is excreted unchanged. The compound was isolated from the urine as the dixanthydryl derivative.
Feeding experiments with alloxan show that this substance is excreted only to a small extent in the urine; the greater part is apparently excreted in the bile. After feeding alloxan we observed a distinct decrease in the output of inorganic sulfur in the urine.
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