Changes in the adenine nucleotide content of preparations of the rat small intestine in vitro.

1. The adenine nucleotide content of rat jejunal mucosa has been measured. For fresh tissue the concentrations of the three nucleotides in the total water are approximately: ATP, 1.4 mM; ADP, 1.0 mM; and AMP, 0.5 mM.2. The adenine nucleotide content of mucosal slices prepared from rat jejunum was about 80% of that of fresh tissue, but the slices rapidly lost nucleotides when they were incubated in vitro. After a 4 min incubation the mucosal tissue contained about 1 mumole/g dry wt. of each of the three nucleotides. This represented only 14% of the ATP, 20% of the ADP and 36% of the AMP originally present. Further incubation had little effect on the ATP and ADP content, but some additional AMP was lost.3. Additions of glucose, amino acids, phosphate, pyruvate, butyrate or glucose-6-phosphate did not prevent the loss of nucleotides from the mucosal slices. The addition of ADP (1 mM) did restore the ATP content of slices to a value close to that of fresh tissue within 2 min, but the nucleotide content declined again on further incubation.4. The respiration rate of mucosal slices falls progressively during incubation in vitro. This decline was largely prevented by the addition of ADP.5. Although nucleotide loss occurred most rapidly from mucosal slices, it was also observed with rings of whole intestinal wall and, less rapidly, with everted sacs.6. ATP added to incubations of mucosal slices disappeared at a rate of about 30 mumole/min. g dry wt.7. These results suggest that the adenine nucleotide content of preparations of rat small intestine studied in vitro is likely to be severely reduced. The addition of nucleotides to the incubation medium produces only a temporary increase in the nucleotide content of the tissue.