Effect of Probenecid on Urate Excretion in the Cat Kidney

The characteristics of probenecid effect on renal urate excretion in the cat were studied by clearance method and compared with those in the rabbit. In the cat GFR was $3.03{\pm}0.09\;ml/min{\cdot}kg$, and endogenous plasma urate concentration was $1.12{\pm}0.57\;{\mu}g/ml$, which is less than that in the rabbit $(3.33{\pm}0.46\;{\mu}g/ml)$. In the rabbit, $FE_{ur}$ was $1.76{\pm}0.08$ and net urate secretion was observed, while, in the cat $FE_{ur}$ was $0.70{\pm}0.02$ and net reabsorption was observed. In the cat $FE_{ur}$ was dependent on urine flow and independent of plasma urate concentration. In the rabbit $FE_{ur}$ was suppressed by infusion of probenecid $(30\;mg/kg\;-0.6\;mg/kg{\cdot}min)$ into femoral vein. In the cat the same dose of probenecid increased $FE_{ur}$ and concomitantly increased urine flow. Thus, an increase in $FE_{ur}$ by probenecid could be considered to be resulted from a change in urine flow. In the cat infusion of probenecid $(2.5\;mg/kg{\cdot}min)$ into renal artery markedly suppressed $FE_{P\;A\;H}$, but the effects on $FE_{ur}$ and urine flow were similar to those when probenecid was infused into femoral vein. These results indicate that in the cat kidney urate filtered through glomerulus is reabsorbed by a probenecid-insensitive mechanism with no evidence for net secretion.