The intrarenal regulation of sodium excretion in the dog.

1. The effect of sodium chloride-containing solution (saline) infusion on sodium excretion has been investigated in kidneys transplanted from donors into the neck vessels of other dogs (perfusors). The dogs (perfusors and donors) had been given sodium-enriched or sodium-poor diets ("loaded" and "deprived' dogs). 2. Three series of experiments were performed: (A) loaded perfusor, loaded donor; (B) deprived perfusor deprived donor; (C) deprived perfusor, loaded donor. 3. Kidneys from deprived dogs, transplanted into deprived perfusors, excreted less sodium after intravenous saline than kidneys from loaded dogs transplanted into loaded perfusors. However, the sodium excretion from the kidneys of loaded dogs transplanted into deprived perfusors was the same as that from the kidneys of loaded dogs transplanted into loaded perfusors. These differences suggest that intrarenal mechanisms are involved in the changes in sodium excretion which follow changes in dietary sodium balance. 4. The intraenal mechanisms included changes in glomerular filtration rate and fractional sodium reabsorption, but not changes in filtration fraction or renin release.