MEASUREMENT AND SIGNIFICANCE OF URINARY APPEARANCE TIME IN THE DOG

Abstract

Measurements of appearance time of substances used in renal physiology were made at varying urine flows in 2 dogs of different sizes. Appearance time is independent of urine flow during moderate diuresis, increasing only at very low urine flows and decreasing moderately during extreme diuresis. The relative constancy of appearance time at urine flows between extreme oliguria and extreme diuresis is attributed to tubular dilatation as the urine flow increases. During moderate diuresis in the dog, appearance time averaged 100 sec. This value can be utilized in making delay time corrections in clearance studies. On the basis of these studies, the commonly used delay time of 150 sec. in clearance studies in man appears to be valid as a correction for moderate changes in plasma concn. of test substances during moderate diuresis. Taking the minimal appearance time in man as 150 sec., it is shown theoretically that, after an instantaneous change in plasma concn. of a solute, approx. 25 min. will be required for the urine again to come into equilibrium with the plasma, a deduction conforming with previously recorded observations.