Cardiovascular, Endocrine, and Renal Responses to Dietary Sodium Restriction
The kidneys are richly innervated by the sympathetic nervous system (Sutters 1992). The role of this sympathetic innervation in the adaptation to changes in dietary sodium intake in persons with spinal cord injury and impaired sympathetic nervous systems warrant study.
|Sutters et al. 1992
|Population: Mean age=28 yr; Gender: males=15, females=0; Level of injury: paraplegia=6, tetraplegia=9; Time since injury=2 mo-1 yr.
Intervention: All individuals received a sodium restriction diet over 5 days consisting of 90 g protein, 90 mmol potassium, and 300 g carbohydrates. Sodium intake was 260 mmol/day for days 1-3 but was reduced to 20 mmol/day on day 4 and 5.
Outcome Measures: Total and fractional urinary sodium excretion, mean arterial pressure, creatinine clearance, plasma renin activity and atrial natriuretic peptide concentration compared between those with tetraplegia (dissociated sympathetic control (DSC)) and paraplegia (intact sympathetic control, (ISC)).
|1. Total and fractional urinary sodium excretion fell in response to sodium restriction in both groups, but the fall in fractional sodium excretion was greater in the DSC group compared to ISC group.
2. Supine mean arterial pressure fell during the low salt period in the DSC group but was unaffected by salt restriction in the ISC group.
3. In the DSC group, creatinine clearance remained constant throughout the low salt period but fell during salt restriction in the ISC group.
4. Plasma renin activity was lower during salt loading in DSC subjects but increased more rapidly and to higher levels in response to salt restriction.
5. Plasma atrial natriuretic peptide concentration was higher in the DSC group during salt loading and salt restriction.
In a study by Sutters et al. (1992) the effects of change from a high to low sodium diet on renal sodium and water excretion and hormonal responses were studied in nine individuals with tetraplegia (dissociated sympathetic control) and in six individuals with paraplegia (intact sympathetic systems). Given the results, the authors suggested that direct sympathetic control of the kidney is not required for renal sodium conservation in response to dietary salt restriction; however, is likely involved in the hemodynamic and hormonal responses.
There is level 3 evidence (from one case control study: Sutters et al. 1992) that sympathetic control of the kidney is not required for renal sodium conservation in response to dietary salt restriction.