Water-Free Na + Retention: Interaction with Hypertension and Tissue Hydration

Abstract

Electrolyte and body fluid homeostasis in higher vertebrates is believed to be fully understood. The paradigm is that Na + is restricted mainly to the extracellular fluid and K + to the intracellular space, where both ions act to hold water and thereby control the extracellular and intracellular fluid volume by their osmotic activity. Na + accumulation thus inevitably leads to water retention. The constancy of the extracellular volume is the task of the kidneys, which control the total body Na + content. More recent data from balance studies in humans have questioned this traditional view, suggesting that large amounts of Na + can be accumulated without accompanying water retention by osmotically inactive Na + retention, or by osmotically neutral Na + /K + exchange. Besides the control of the body Na + content by the kidneys, redistribution of body electrolytes hence provides an extrarenal regulatory alternative in the maintenance of body fluid volume and blood pressure control. Show more