Relation between sodium intake, renal function, and the regulation of arterial pressure

The long-term regulation of arterial pressure requires the maintenance of a balance between sodium and water intake and sodium and water excretion. Normal salt and water balance leads to stable body fluid volumes and the maintenance of normal renal function is critical to establishing extracellular fluid volume homeostasis. This review focuses on the role of the kidney in the long-term control of salt and water balance with particular emphasis on the relations between sodium intake, the renin-angiotensin-aldosterone system, renal sympathetic nerve activity, and the regulation of arterial pressure via renal sodium and water excretion. The accumulation of evidence in recent years demonstrates that low level elevation of renin release, circulating angiotensin II or aldosterone, or activation of renal sympathetic outflow may alter renal function such that normal natriuretic and diuretic responses to arterial pressure are significantly impeded. Under these circumstances, the maintenance of normal sodium and water excretion requires a significant elevation of arterial pressure. Thus, compromised renal function leads to elevation of arterial pressure to maintain adequate sodium and water balance during periods of increased sodium intake. The resultant chronic elevation of arterial pressure then becomes a compromise that is used by the kidneys to maintain normal extracellular body fluid volumes.