Quantitative urine collection in renal clearance studies in the dog

A double-walled urinary catheter is described which allows rapid and quantitative urine collection at short time intervals. The catheter consists of a polyurethane outer cannula in which a small Teflon cannula is inserted. The essential of the catheter is that at the end of a collection period, residual urine in the bladder can be collected completely via the outer cannula by flushing the bladder with physiological salt through the inner cannula. In this manner urine can be collected in a very reproducible way at intervals down to 5 min. The use of the catheter was illustrated in a study on the renal clearance of hippuric acid in the dog. Plasma concentration and renal excretion rate were followed after i.v. injection of 0.9 g sodium hippurate. In accordance with previous studies, it was found that the renal excretion of hippuric acid consisted of glomerular filtration and active tubular secretion. A large variability was observed in the tubular transport maximum (3,800-11,600 micrograms/min) and the Michaelis-Menten constant (22-190 micrograms/ml), which were used to characterize the secretory system. The interpretation and value of these transport parameters is discussed briefly.