The effect of mercurial diuretics on the excretion of water.

In experiments on 11 normal subjects and on three dogs it has been observed that mercurial diuret-ics do not prevent the stimulation of water absorption and formation of hypertonic urine which characteristically follows the infusion of Pitressin. Furthermore mercurial diuretics only rarely increase urine flow when administered in the course of maximal water diuresis. These two facts are interpreted as meaning that the diuretic agents have no primary effect on the reabsorption of water. Rather, increased urine flow results secondarily from increased elimination of ions. IN THE treatment of edematous patients, dosage and frequency of administration of mercurial diuretics are customarily gaged by weight loss. Such loss of weight represents largely loss of water from the extra-cellular fluid compartment. Although it is generally conceded that mercurial diuretics block some fraction of the renal tubular absorption of sodium and chloride, no conclusive evidence exists of whether or not they affect the absorption of water directly.' It is possible that loss of ions obligates in some way the excretion of equivalent quantities of water. On the other hand, renal tubular absorption of water per se might be inhibited to some extent by the diuretic agent. The present investigation was undertaken to provide experimental evidence on this point. According to present concepts, large quantities of fluid, approaching 160 liters per day, are filtered through the glomeruli of normal man.2 Ordinarily all but one or two liters are absorbed as the filtrate progresses through the renal tubules. The absorption of the major fraction of this water, up to 140 liters per day, is presumed to occur passively in the proximal segment in consequence of the active absorption of salts, glucose and other valuable constituents from the tubular fluid.3 The absorption of these solutes, especially ions, is thought to establish the osmotic force which returns water to the blood stream. The absorption of the remainder of the water, up to 20 liters per day, is presumed to occur in more distal portions of the nephron, either in the distal segment of the renal tubule or in the collecting duct. The absorption of this moiety is independent of the absorption of solutes. At least solutes may be absorbed without the absorption of equivalent quantities of water and to some extent water may be transported actively, independently of solutes, and against an osmotic gradient. Two major factors condition completeness of absorption in this distal portion of the …