MECHANISM OF INCREASED RENAL SODIUM EXCRETION FOLLOWING MANNITOL INFUSION IN MAN

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Abstract
When a slightly hypotonic or isotonic solution of mannitol was infused into 3 sitting water-loaded sub-jects, a marked increase in urinary Na excretion took place despite a decrease in filtered Na load. The natriuresis was not ascribable to cellular dehydration since hypotonicity of the body fluids was present throughout the procedure. Nor was expansion of extracellular volume alone the natriuretic stimulus since under these conditions a similar expansion with hypotonic salt solutions is an ineffective stimulus. Hence the chief site of action of mannitol in decreasing Na reabsorption appears to be in the renal tubule.