Production of Hypertonic Urine in the Absence of Pituitary Antidiuretic Hormone1

Abstract

The mechanism by which pituitary antidiuretic hormone (ADH) produces its renal effect has not been clearly established. Under ordinary conditions, in the absence of ADH, urine of a con- centration considerably below that of plasma is produced in large volume. With increasing amounts of ADH, administered or secreted, the osmotic pressure of the urine rises to and above that of plasma. With respect to total water bal- ance, the quantitatively more important contribution to water economy is the change between maximally dilute and isotonic urine, since this, in normal man, may involve a change in water ex- cretion in excess of 10 ml. per minute. The fur- ther saving of water effected by the elaboration of hypertonic urine is a relatively small one, amount- ing, at usual rates of solute excretion, to not more than an additional 1 or 2 ml. per minute. Thus, although it is commonly stated that the function of ADH is to cause the excretion of a hypertonic urine, its more important function might be better defined as preventing the excretion of a dilute urine.