Enhanced renal sympathetic nerve activity in response to salt loading in rats

To analyze the conflicting data on the relationship between sodium intake and sympathetic activity, the effects of a chronically excessive intake of sodium on renal sympathetic activity and blood pressure were investigated in normotensive rats. Renal sympathetic activity was estimated by urinary excretion of free norepinephrine (NE) and the turnover of NE in the kidneys. Blood pressure increased in rats receiving a high sodium diet when compared with that of the basal sodium diet. Urinary-free NE, epinephrine (E) and dopamine (DA) excretions in rats receiving a high sodium diet were enhanced significantly from those in the basal sodium diet. The turnover of NE in the kidneys was more enhanced in the high sodium group than in the basal sodium group. By blocking the sympathetic tone with ganglionic blockade, hexamethonium, enhanced excretion of urinary NE and elevation of blood pressure in response to salt loading were blocked to the levels of the basal sodium diet. These results suggest that a chronically excessive intake of sodium enhances the renal sympathetic and adreno-medullary activities, leading to a rise in blood pressure in normotensive rats.