Nonuremic hyperosmolality produced by sodium depletion.

FALK, J. L. AND M. TANG. Nonuremic hyperosmolality produced by sodium depletion• PHYSIOL. BEHAV. 10(4) 793-799, 1973.-Rats were rapidly sodium depleted by a 4-hr intraperitoneal dialysis against isotonic glucose, and various serum and urine measures were taken at 4, 12 and 20 hr from the start of dialysis for dialyzed and control groups. No food or water was allowed during this postdialysis period. At 4 hr, dialyzed animals were hyponatremic, hypovolemic, hyposmolal and oliguric. This was followed by a general picture of renal sodium and chloride saving and a return of relatively normal urine volume. Plasma volume and electrolyte concentration became approximately normal as did urine glucose and urea clearances. However, serum osmolality progressively increased relative to control groups, and at 20 hr was 22.5 mOsm greater than controls. Of this difference, 15.1 mOsm was not accounted for by the osmotic equation calculated from serum sodium, glucose and blood urea nitrogen. These body water distortions in concentration and locus are discussed in the light of increased water and NaCl intakes observed in our previous research.