The relation of blood sodium concentration to blood pressure in the rat.

Rises or falls in blood sodium concentration ([Na]) within a physiological range of +/- 15 mmol/l, sustained for 5 h, were produced in the rat by intraperitoneal dialysis with physiological salt solutions containing variable amounts of Na. In general, systolic and diastolic blood pressure rose and fell in direct relation to the alteration in [Na]. Solutions of equivalent osmolarity produced changes in blood pressure that were the inverse of those induced by Na. These effects could not be explained in terms of changes in blood or extracellular fluid volume, and indicated the need for an exploration of the partition of Na and water across the vascular smooth muscle cell.