Salvage of adenosine, inosine, hypoxanthine, and adenine by the isolated epithelium of guinea pig jejunum

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Abstract
The metabolism of adenosine, inosine, hypoxanthine, and adenine (labelled with 14C in the carbon 8 position) at a concentration of 5 × 10−6 M was studied in isolated epithelium of guinea pig jejunum. When adenosine or adenine was added to the antiluminal side of the epithelium, two-thirds or one-half, respectively, of cellular radioactivity was incorporated into the nucleotide fraction, mainly in the form of adenine nucleotides. Nucleotide synthesis from inosine or hypoxanthine was significantly smaller than that from adenosine. By contrast, another metabolic pattern was found after luminal administration of adenosine, inosine, or hypoxanthine: the incorporation rate into the nucleotide fraction was equally high and the label was recovered in IMP and adenine nucleotides to about the same extent with all three substrates. Purine riboside (10−4 M) significantly depressed nucleotide formation from adenosine, with respect to IMP formation in particular, while no change was observed in inosine or hypoxanthine salvage. The results suggest compartmentation of the enzymes of purine metabolism within the intestinal mucosa. The significance of this conclusion with regard to the salvage pathway is discussed.