THE MODE OF ACTION OF A MERCURIAL DIURETIC IN MAN

the diuretic action of organic mercury compounds is renal rather than extrarenal. The use of clear-ance techniques has further shown that the glo-merular filtration rate does not increase in man during a mercurial diuresis (3, 4). The increased rate of water excretion must, therefore, be due to diminished tubular reabsorption. Attempts to carry the analysis still further have led to divergent views. Duggan and Pitts (5) conclude that the site of action is in the distal seg-ment of the tubule, whereas Mudge, Foulks, and Gilman (6) and Weston, Grossman, and Leiter (7) believe it is in the proximal segment. In this paper we present data which we consider to sup-port the former view. METHODS The subjects were normal male medical students or doctors. Except where it is stated to the contrary, the subjects came to the laboratory in the morning, having taken nothing by mouth since the previous evening. The experiments were begun as near 9:30 a.m. as possible. Urine was collected at 30-minute intervals by voluntary micturition, without a catheter; the collection periods were usually reduced to 15 minutes at the peak of the diuresis. The mercurial diuretic used was Mersalyl, obtained as a solid from British Drug Houses Ltd.; unless otherwise stated, the dose was 0.2 Gm., which was dissolved in 20 ml. sterile distilled water and injected intravenously as soon as possible after solution. The injection was given slowly over a period of 10 minutes to avoid possible toxic effects on the heart resulting from a momentarily exces-sive blood level of the drug. No theophylline was given with these injections. During the experiments the subjects sat in a chair or reclined on a couch; their activity was restricted to that necessary for passing urine. They took nothing by mouth, except as stated in the text. Smoking was prohibited. The chemical methods used were as follows: Sodium: direct reading flame photometer; Chloride: electrometri