Quantification of End-Products of Purine Catabolism in Dogs Fed Diets Varying in Protein and Purine Content
Urate and xanthine stones result from urine saturation of end-products of purine catabolism. In dogs urinary excretion of urate and xanthine is affected by breeds (i.e., Dalmatians) or drug treatment (allopurinol). To date, a purine and severely protein restricted diet has been recommended to reduce urinary xanthine and urate excretion in affected dogs. The purpose of this study was thus to study the influence of 3 dry-expanded diets with different purine and protein content on urinary purine end-product excretion in dogs.
Six healthy neutered-female medium Schnauzers (8.8 ± 0.44 y) were included in the study. They were successively fed 3 commercial diets with various purine and protein content: A: a poultry and corn-based diet (25% protein), B: an egg and rice diet (18% protein)and C: an egg and rice diet (9.8% protein as fed). Dogs were fed based on the equation 132 kcal/kg0,75/d. Water was available ad libitum. After five days of adaptation, dogs were moved in metabolic cages and all urines were collected over 5 days. Purines (adenine, guanine, hypoxanthine, xanthine) and uric acid were assayed in the diet by HPLC. Urine samples were pooled and conserved at -20°C pending assays. End-products of purine catabolism (hypoxanthine, xanthine, uric acid and allantoin) were quantitatively assayed by capillary electrophoresis. Data were analyzed by repeated measured ANOVA. Results are expressed as the mean ± SEM.
Dogs maintained their weights over the duration of the study. Daily mean consumptions of purines were: for diet A: 2727 ± 63, for diet B: 686 ±19 and for diet C: 465 ± 18 µmol/d. Mean daily urinary excretion of total purine end-products were significantly higher for diet A 6063 ± 497 than both diet B: 3962 ± 212 and diet C: 3309 ± 353 µmol/24h. The ratio of uric acid/(uric acid+allantoin) representing the proportion of uric acid not converted into allantoin and excreted in urine did not vary depending on the diet (A: 11.8 ± 3.9, B: 11.2 ± 3.3, C: 9.8 ± 2.5 %) but significant individual variations were noted between dogs (mean 11%, range 4.1-21%).
This study confirms the great influence of purine intake on purine end-products excretion. It shows that severe protein restriction is not mandatory to decrease purine end-product urinary excretion. Measurements of total purine end-products excretion might be a more relevant method to assess a benefit of the diet on purine metabolite excretion in normal dogs than the excretion of uric acid. Evaluation of the ratio: uric acid/(uric acid+allantoin) in urine could be helpful in identifying dogs with increased risk of forming purine uroliths.