Absorption and Metabolism of Orally Administered Purines in Fed and Fasted Rats

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Abstract
Two experiments were conducted to determine the extent of absorption and metabolism of dietary purines in fed and fasted male Sprague-Dawley rats intubated with 12 to 17 µCi of [8-14C]adenine, guanine, hypoxanthine or xanthine. In experiment 1, the incorporation of radio-activity over a 24 hour period into liver, heart, kidney, spleen, urine, plasma, erythrocytes, gastrointestinal tract plus contents, carcass and expired CO2 was measured. All the rats were fasted overnight, and one-half were given a single meal of a commercial diet 1 hour prior to intubation. In experiment 2, the incorporation of radioactivity from the same purines over a 24 hour period into liver, urine, gastrointestinal tract and its contents was measured. All the rats in this experiment were fasted overnight. One-half were given a single meal of a purine-free diet 1 hour prior to intubation. The radio-activity in all of the administered purines was for all practical purposes quantitatively absorbed and was extensively recovered in the urine during the test period. Adenine was more extensively incorporated into liver, kidney, heart and spleen than was guanine, hypoxanthine or xanthine. The incorporation of guanine and hypoxanthine into liver was similar. Xanthine was minimally incorporated into all tissues. Only adenine was more extensively incorporated into the tissues of fasted rats than of fed rats. Allantoin was the major end product of metabolism for all the labeled purines given. These results demonstrate that dietary purines are extensively absorbed and excreted in urine with little tissue incorporation. The fed/fasted differences in adenine incorporation suggests that a complementary relationship exists between de novo purine synthesis, which is dominant during the fed state, and purine reutilization, which is dominant during the fasted state.