The effect of salt loading and salt depletion on renal function and electrolyte excretion in man.

Glomerular filtration rate (GFR), renal plasma flow (RPF), and electrolyte excretion were studied in 17 patients subjected to salt depletion and loading. Salt depletion led to maximal renal salt conservation with the average GFR and RPF slightly decreased. Salt loading produced increased excretion of sodium and chloride with the average GFR and RPF slightly increased. Since the decreased electrolyte excretion with salt depletion and increased electrolyte excretion with salt loading were essentially independent of the direction of change in GFR and RPF, it is inferred that tubular absorptive activity is a more significant factor in achieving electrolyte balance than are GFR changes.