Ontogeny of renal uric acid excretion in the mongrel puppy.

Renal uric acid excretion was examined in 35 mongrel puppies at 1, 30, 60 and 90 days of age and in seven mature mongrel dogs. Uric acid concentrations in plasma and urine were determined using a uricase fluorometric method. Clearance of inulin increased with postnatal age; however, fractional excretion of uric acid (FEUA) decreased from 83% at birth to 51% at 90 days of age (r = -0.675, P less than 0.001). Filtered uric acid and net reabsorption of uric acid increased with postnatal development. The decline in FEUA with postnatal age was unrelated to binding of uric acid to plasma proteins or to urine flow rate. A direct correlation was observed between clearance of uric acid (CUA) and clearance of sodium (CNa) during early development (r = 0.48, P less than 0.001). These data indicate that postnatal maturational patterns of renal urate excretion in mongrel puppies are similar to human newborns.