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Absorption of a dipeptide and its constituent amino-acids has been studied by a perfusion technique in a patient with cystinuria and in a normal subject. Though the cystinuric patient was unable to absorb the dibasic amino-acid lysine in its free form, the dipeptide glycyl-L-lysine was well absorbed. Both free lysine and glycyl-L-lysine were well absorbed in the normal subject. This finding suggests that the reason that clinical malnutrition does not occur in cystinuria, despite defective intestinal absorption and heavy renal loss of dibasic amino-acids and cystine, is that these amino-acids can be absorbed in the form of oligopeptides.

The conversion of hypoxanthine and xanthine to urate via xanthine oxidase (Xanthine: oxygen oxidoreductase (E.C. 1.1.3.22.) may when ischaemic tissues are re-oxygenated generates radical oxygen species. Such ischaemia may be involved in the adverse effects of non-steroidal anti-inflammatory drugs (NSAIDS) on the human intestine where high levels of xanthine oxidase are known to be present. However little qualitative or quantitative information concerning the nucleotide content of intestine is available.

High Performance Liquid Chromatography is the accepted method for the study of nucleotides in cell and tissue extracts. A variety of chromatographic separations have been described but to date the use of microparticulate anion exchange procedures remains the most popular. However the accurate analysis of cell extracts requires careful attention to both sample preparation and chromatographic operation. This study records the results of some 14 years experience and many thousands of analyses. Optimal conditions for the acid extraction of cellular nucleotides to maximise recovery, minimise nucleotide Interconversions, maximal removal of protein and excess acid extractant have been defined. For RBC's these are 1 part cells to 2.5 parts 12% TCA with acid removal with ether or Alamine /Freon. Protein removal was 99.8% efficient Cyclic nucleotides e.g cXMP are excellent internal standards. For the reliable separation of standard, normal and abnormal cell extracts by anion exchange chromatography over time with any one column, adherence to the following conditions was critical. Buffer pH needs to be adjusted to maintain difficult separations e.g. ADP/NADP, GMP/IMP, buffer molarity should be regularly reduced to counter column ageing and maintain resolution and potential interferences such as EDTA, Ficol-hypaque should be avoided.