Mechanism of Mercurial Diuresis in Hydropenic Dogs

Abstract

Mercuhydrin, 5-9 mg./kg. of body wt., was administered intraven. to barbitalized dogs. They had been deprived of water for 20 hrs. and food for 10 hrs. preceding expts., and were excreting urine at flows of 0.12-0.33 cc./min./ m2., with osmotic activities of 1376-1658 mosm./l. Urinary flow increased rapidly 45 min. after injection attaining values as high as 8 cc./min., while osmotic activity, falling to 400-500 mosm./l., remained hypertonic to plasma. Flows remained at maximal levels for 30 min., and gradually decreased to hydropenic levels in the next 90-100 min. In plasma, osmotic activity and composition of solutes were unchanged during preliminary and diuretic periods. During diuresis, the relationship between urinary flow and effective osmotic load was characteristic of the constant pattern found in hydropenic diuresis forced by a wide variety of loading solutes. Na and Cl, reaching concentrations of 200-300 meq./l. each, accounted for 80-85% or urinary solutes. The rate of Na loss was as high as 1.2 meq./min./m2. Clearances of inulin and PAH, when measured, were essentially unchanged. It appears that mercurial action, at a proximal tubular site, causes a large solute load, mainly Na and Cl, to be presented to the distal tubule. The distal tubule responds osmometrically, elaborating a final urine, the volume of which, like that in any osmotic diuresis, is dependent on the number of osmotically active particles claiming excretion.