NATURE OF FLUIDS WHICH FUNCTIONALLY DISTEND THE KIDNEY

Abstract

The nature of the fluid draining from the dog kidney, after its artery was occluded, was studied. Samples of systemic arterial blood, renal venous blood and urine were also analyzed. Fluid draining from kidney after occlusion is a mixture of vascular blood and another fluid designated as "diluting fluid," each contributing half to the composite mixture. In volume the mixture is 26% of the functionally distended kidney. With the assumption that the renal extracellular fluid can be considered a simple mixture of blood plasma and a cell-free fluid, the composition of the "diluting fluid" was deduced from the known compositions of vascular blood and total fluid draining. The ratios of its content in a given substance to that in systemic (or renal venous) plasma are: for Na and Ca, 1.0; K, 1.5; Cl, 1.2; PO4, 2.0; urea, 1.8; plasma protein, 0.3; albumin, 0.4; glucose, 0.4, and osmolarity, 1.2. The fluid bears little or no relation to urine, especially since the urine varied considerably between individual dogs whereas the "diluting fluid" was relatively constant in composition. It was also found that the hematocrit of the fluid draining after arterial occlusion progressively de creased as it flowed out, until the last portion contained only 5% red cells. It is concluded that since renal lymph has approximately the same composition in protein, urea, glucose, and inulin as does "diluting fluid," the latter is, in probability, renal interstitial fluid. Under the conditions of the experiment, it drains out of the kidney slowly relative to blood drainage. It is large in volume, particularly when compared with the capillaries that nourish it. These data furnish an explanation for the observation that the kidney is apparently naturally distended with a fluid disproportionately rich in plasma protein. The organ is distended with blood and, as well, interstitial fluid; the protein content of the two compartments adds up to considerably more than might be expected on the basis of the kidney''s red cell content.