Sodium intake alters the effects of norepinephrine on blood pressure

To examine the interactions between sodium balance and the sympathetic nervous system, we studied eight normotensive men after high (800 mEq/day) and low (10 mEq/day) sodium intake. We measured blood pressure (BP), arterial, venous, and urinary norepinephrine (NE) before and during incremental infusion of NE. We found significant direct, linear relationships (p less than 0.001) between the dose of NE infused and arterial and venous NE levels, and with mean arterial BP at both levels of sodium balance. In addition. the sensitivity was greater and the threshold of pressor response to NE as well as the basal concentrations of NE in arterial and venous plasma significantly lower (p less than 0.05) after the high sodium period. These observations expose heretofore unrecognized qualitative and quantitative interactions between sodium balance and NE that are capable of influencing BP in man.