Purine availability and metabolism in dogs fed single-cell protein or RNA

For the evaluation of single-cell protein (SCP) the proportion of dietary purines made available by digestion and absorption was estimated with dogs (Dalmatian) in total urine collection experiments. The animals received a low purine control diet with 25% casein, diets with 25-100% replacement of casein by a bacterial SCP grown on methanol, and the control diet plus yeast RNA purine equivalent to SCP diet. Nucleic acids, bases, and purine metabolites were determined by reversed-phase high-pressure liquid chromatography. The quantitative influence of dietary purines (x) on renal purine excretion (y) was described by the equation (millimoles per day) y = 0.57x + 3.52 (r = 0.955) indicating the endogenous excretion rate of 3.5 mmol/day and the metabolic availability of 57% of ingested purines. As the ratio of urate to allantoin increased with purine intake, individual equations were established for both metabolites. On the control diet + RNA and SCP diet (100% replacement for casein), purine intakes of 20.0 and 18.2 mmol/day resulted in purine excretion values of 7.3 and 11.4 mmol/day (P less than 0.05). The proportion of free bases in the latter diet appeared as the main reason for this differences. Other influences are discussed.