Studies in vitro of digestion and absorption of pyrimidine nucleotides by the intestine.

,4 series of enzymes which result in the degradation of nucleic acids to nucleosides and free bases is known to be present in the gastrointestinal tract. Although it is generally believed that nucleic acids must be hydrolyzed before absorption, it is not entirely clear at what stage absorption occurs. Studies with Nls-labeled yeast nucleic acid fed to rats indicated that some N15 appeared in tissue pyrimidines (1). As free pyrimidines given by mouth are not well utilized for nucleic acid formation (2, 3), it may be concluded that absorption occurs before the breakdown in the lumen of the intestine proceeds to the stage of the free base. Nucleosides, on the other hand, are known to be converted readily to nucleic acids (4). The present study was undertaken in an attempt to correlate the degradative reactions occurring in the lumen of the intestine with the absorption of the products of these reactions. Small sacs of intestine in vitro made possible the sampling of both mucosal and serosal sides of the intestinal wall during digestion and absorption of pyrimidine nucleotides.