THE DETERMINATION OF THE RENAL CLEARANCE OF DIODONE AND THE MAXIMAL TUBULAR EXCRETORY CAPACITY FOR DIODONE IN MAN

1. The principles devised by the authors [1949] for the determination of the renal clearance of inulin have been applied to the determination of the renal clearance of diodone and the tubular excretory capacity for diodone. 2. Following the intravenous injection of diodone in amounts suitable for the measurement of both renal clearance and tubular excretory capacity, the volume of distribution of diodone continues to increase for the duration of the experiments. It is concluded that equilibration of diodone between the plasma and the extravascular component of the volume of distribution does not occur under the conditions of the experiment. 3. Formulæ are derived for the renal clearance of diodone and the maximal tubular excretory capacity for diodone incorporating functions which are demanded by the failure of the establishment of equilibration. 4. The formula for the renal clearance of diodone is applied to fourteen subjects possessing widely different clearance values, and the formula for the maximal tubular excretory capacity for diodone is applied to twelve of these subjects. The values calculated by the formulæ agree closely in every case with the average values experimentally determined, following intravenous injections of diodone. 5. The calculative errors introduced into the formulæ by the simplifying assumption that the volume of distribution of diodone is linearly related to time, between defined limits of time, are shown to be of similar magnitude to the limits of the error in the chemical determination of diodone in the plasma. 6. The formulæ can be applied without the need for accurate urine collection over short clearance periods. They necessitate the passage of urine approximately 25 and 120 minutes (for the maximal tubular excretory capacity for diodone) and 20 and 60 minutes (for the renal clearance of diodone) after the injection of known amounts of diodone, and a minimum of two blood samples for each determination taken at the time of urine passage. 7. The errors introduced in the determinations of inulin and diodone clearance and the maximal tubular excretory capacity for diodone by sampling venous blood are discussed briefly. 8. The results of a further five estimations of inulin clearance employing the authors' method (loc. cit.), and their comparison with average values experimentally determined, are also included.