PRODUCTION OF INCREASED RENAL SODIUM EXCRETION BY THE HYPOTONIC EXPANSION OF EXTRACELLULAR FLUID VOLUME IN RECUMBENT SUBJECTS 1

Abstract

Neither the expansion of plasma volume nor of total body water appear to increase the renal excretion of Na. To study the effect of expansion of the extracellular compartment, expts. were devised in which the volume of extracellular water was expanded at the same time that the concns. of Na and chloride therein were reduced. Under these conditions any renal or extra-renal effects ascribable to an increased concn. of these ions either in extracellular fluid or in glomerular filtrate could be eliminated from consideration. Such hypotonic expan- sion of extracellular fluid volume in recumbent subjects was demonstrated to lead to an increased urinary excretion of Na although the filtered load presented to the renal tubules was actually diminished. The failure of a similar expansion of extracellular volume significantly to augment Na excretion in seated subjects was interpreted as suggesting that the locus of action of expanded volume (or some associated factor) is in the cephalad portion of the body. The hypothesis is offered that contraction of extracellular volume (or an associated factor) in the cephalad portion of the body may be a stimulus for sodium retention. The applicability of this hypothesis of salt retention of heart failure and cirrhosis of the liver is discussed.