SEPARATE RENAL FUNCTION STUDIES IN DOGS WITH CHRONIC UNILATERAL RENAL ARTERY OBSTRUCTION. THE EFFECT OF HYPERTONIC UREA INFUSIONS.

The left main renal artery was constricted in 41 dogs for intervals of 7 to 30 days. Separate urine collections from each kidney were then made during water diuresis and, in 28 of the dogs, during hypertonic urea diuresis. 'The rnost sensitive criteria of renal artery obstruction were combinations of urine volume and creatinine concentration ratios or of sodium and creatinine concentration ratios. To demonstrate enhanced water reabsorption by t he tubules of a kidney, there is no diagnostic advantage in the use of any one over another of the ratios of urine creatinine, urea, or para-amino hippurate. 'The filtration fraction of the constricted kidney was the same as that of the control. Thus the simpler measurement of each kidney's endogenous creatinine clearance offers the same assessment of relative kidney function as the technically more difficult measurement of separate para-amino hippurate clearances. When, under water diuresis, the urine concentration ratios of sodium and creatinine, as well as the urine volume ratio, are diagnostic, then urea infusions tend to blunt them. Conversely, when these ratios are not diagnostic, urea infusions tend to enhance them. Thus, for the greatest efficiency in the diagnosis of renal artery obstruction, separate urine collections should be made under conditions of both water and hypertonic urea diuresis.