MECHANISM OF UREA EXCRETION

1. Urea is present in the cells of the proximal convoluted tubule in a concentration higher than that of the blood or than that of the cells of any of the other kidney tubules. 2. Such a condition can only be reconciled to an assumption of an active secretion (excretion) on the part of these cells. 3. Urea also passes through the glomerular filter with the other crystalloids of the blood plasma. 4. The final concentration of urea is due to the above mentioned secretion by the proximal convoluted tubule, and to the absorption of water in other parts of the tubule.     

THE NUMERICAL LAWS GOVERNING THE RATE OF EXCRETION OF UREA AND CHLORIDES IN MAN : I. AN INDEX OF UREA EXCRETION AND THE NORMAL EXCRETION OF UREA AND CHLORIDES.

1. The excretion of urea and of chlorides in the normal individual is carried out according to definite laws, capable of numerical expression. 2. The rate of excretion of urea and of sodium chloride is determined by the concentration in the blood, the rate of water output, and indirectly by the weight of the individual. 3. The threshold of sodium chloride excretion is practically constant at about 5.62 grams of sodium chloride per liter of plasma. Slight variations in the threshold occur in normal individuals. 4. The rate of excretion of urea under the conditions found at any time can be measured directly in terms of the normal by an index of urea excretion.     

THE NUMERICAL LAWS GOVERNING THE RATE OF EXCRETION OF UREA AND CHLORIDES IN MAN : II. THE INFLUENCE OF PATHOLOGICAL CONDITIONS AND OF DRUGS ON EXCRETION.

A method of measuring the rate of excretion of urea, in terms of the normal, as presented in a preceding paper, has been applied to the study of diseased conditions and of the action of drugs. Simultaneous observations on chloride excretion have been made by comparing the concentration of chlorides actually found in the plasma with the theoretical amount, calculated from the rate of excretion. Observations made in this way have been found applicable to the study of various diseased conditions.     

THE EFFECT ON THE RATE OF UREA EXCRETION OF CARMINE DEPOSITION IN THE CELLS OF THE RENAL TUBULES

The evidence that urea is present in high concentration in the cells of the convoluted tubules of the kidney and is passing through these cells has been reviewed. Following the deposition of a large amount of carmine in the cells of the convoluted tubules the rate of urea excretion, as measured by the relation of the rate of urea excretion to the blood urea concentration, is increased. This is interpreted as due to blockage or damage to the cells of the convoluted tubules which interferes with their usual function of absorption of urea and other substances from the glomerular filtrate and hence increases the amount of urea which reaches the bladder urine at a given blood urea concentration.