Abstract
The intestinal absorption of thymine and uracil was investigated in the anesthetized rat. These substances appear to cross the intestinal epithelium by a combination of two processes: 1) a specialized transport process characterized by saturation kinetics and competition by certain other substances; and 2) passive diffusion, the rate of which is not affected by the presence of other substances.
Uracil is a competitive inhibitor of thymine transport, and the two compounds show the same affinity for the transport mechanism.
Thymine and uracil are actively transported across the intestinal wall in vitro.
The failure of D-glucose and L-histidine to depress the absorption of thymine suggests that the active transport mechanism described here is different from those responsible for the absorption of certain sugars and amino acids.
The depression of thymine transport by hypoxanthine, 6-azauracil, 6-azathymine and cytosine suggests that the transport process may be involved in the absorption of a variety of pyrimidine and purine derivatives and structurally related foreign compounds.
Footnotes
- Received August 8, 1959.
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