SOME EFFECTS OF VARIATION IN SODIUM INTAKE AND OF DIFFERENT SODIUM SALTS IN NORMAL SUBJECTS

Modifying Dietary Sodium and Potassium Intake: An End to the 'Salt Wars'?

Excessive salt intake raises blood pressure, but the implications of this observation for human health have remained contentious. It has also been recognized for many years that potassium intake may mitigate the effects of salt intake on blood pressure and possibly on outcomes such as stroke. Recent large randomized intervention trials have provided strong support for the benefits of replacing salt (NaCl) with salt substitute (75% NaCl, 25% KCl) on hard outcomes, including stroke. During the same period of time, major advances have been made in understanding how the body senses and tastes salt, and how these sensations drive intake. Additionally, new insights into the complex interactions between systems that control sodium and potassium excretion by the kidneys, and the brain have highlighted the existence of a potassium switch in the kidney distal nephron. This switch seems to contribute importantly to the blood pressure-lowering effects of potassium intake. In recognition of these evolving data, the United States Food and Drug Administration is moving to permit potassium-containing salt substitutes in food manufacturing. Given that previous attempts to reduce salt consumption have not been successful, this new approach has a chance of improving health and ending the 'Salt Wars'.

The rapid adjustment of renal sodium excretion to changes in dietary sodium intake in sheep

The rapidity with which the kidney alters sodium excretion (ENa) in response to changes in dietary Na was studied in Merino sheep by analyzing hourly ENa for three control days, and then for three days after a change in Na intake. On a control diet of 117 mmol Na, sheep had a pre-feeding ENa of 3.5 mmol/hr., a striking post-feeding natriuresis that began 2 hours after feeding (less than 0.01), peaked at 4 hrs. and then declined to pre-feeding levels 7 hrs. after feeding. When in balance on a high Na diet the feeding of a low Na meal resulted in marked depression of ENa within 4 hours after feeding. On a low Na diet, a 100 mmol Na meal resulted in an increase in ENa within 4 hours but a 50 mmol Na meal did not. Thus, the sensitivity of post-feeding natriuresis is between 50 and 100 mmols Na. As post feeding natriuresis is a naturally occurring physiological event it should provide a useful paradigm for the investigation of mechanisms controlling Na balance.

Effects of posture on renal excretion of sodium and chloride in orthostatic hypotension

Large decreases in the rates of sodium excretion, chloride excretion, and glomerular filtration were observed in patients with orthostatic hypotension when they assumed the upright posture following a period of recumbency. When they returned to the recumbent position, sodium excretion typically was not restored immediately in spite of immediate restoration of filtered sodium load. The decreased sodium excretion found to occur in patients with orthostatic hypotension when they are in the upright posture is considered to be due in part to the decreased filtered sodium load and in part to changes in tubular reabsorption that are independent of filtered sodium load.