Excretion of Urea and Creatinine in the Dog in Relation to Rate of Urine Formation

Abstract

Austin, Stillman and Van Slyke 1 on the basis of data obtained on a series of normal men, showed that when the urine flow was progressively increased from very low values the urea clearance also increased until the rate of urine excretion reached a value they termed the augmentation limit. At rates of urine excretion above the augmentation limit there was found to be no further increase in urea clearance. Subsequently this description has been accepted for dogs by Jolliffe and Smith 2 and Summerville, Hanzel and Goldblatt, 3 and it has been tacitly assumed by Van Slyke, Rhoads, Hiller and Alving 4 in their study of factors controlling urea excretion. A maximum urea clearance has also been posited by Dominguez 5 in his mathematical treatment of the relation existing between urea clearance and urine flow at rates of urine formation below the augmentation limit. The value fixed for the augmentation limit in the dog has been variously stated to be from 0.2 to 0.4 cc. per minute, depending in part upon the size of the animal, and also upon the level of the maximum clearance, which can be varied by changing protein intake.

Recent evidence has made it possible to accept the creatinine clearance as a measure of the rate of glomerular filtration in the dog. (Shannon, 6 Van Slyke, Hiller and Miller 7 ), even at very high U/P ratios (Shannon 8 ). The present observations were made to examine the relations between the rate of glomerular filtration and the rate of excretion of water, and the effect of these variables upon the urea clearance.

There is no standard of reference by which the clearances of various individual dogs can be converted to a common value. For this reason it was apparent beforehand that the data from each dog should be treated separately.