Origin of sodium ions appearing in the venous blood plasma during acute venous congestion and hemorrhagic hypotension: a study on kidneys and skeletal muscle of dogs.

We studied the origin of sodium ions which appeared in a higher concentration in the venous blood plasma obtained from the renal or femoral vein, than in the arterial blood plasma during acute renal venous congestion, acute venous congestion of hindlimbs and acute hemorrhagic hypotension. We measured the sodium concentration in the blood plasma as well as in hemolyzed blood obtained with sonication. In addition, sodium contents of the kidneys and skeletal muscle were determined. All experiments were performed on anesthetized mongrel dogs. Sodium contents of the kidneys and skeletal muscle of hindlimbs, in terms of milliequivalent per gram dry tissue weight, was decreased significantly 30-40 min after exposure of the kidneys and hindlimbs to acute venous congestion, or after exposure of hindlimbs to hemorrhagic hypotension, indicating a release of sodium ion into the blood stream. The sodium ion concentration became slightly higher in the venous blood than in the arterial blood, in terms of both blood plasma and hemolyzed blood, during 15-30 min of exposure of hindlimbs to local venous congestion or hemorrhagic hypotension, again indicating a release of sodium ion into the blood stream. However, acute renal vein congestion caused the sodium ion concentration to become slightly higher in the venous blood than in the arterial blood, only in terms of blood plasma, and not in terms of hemolyzed blood, indicating that red blood cell sodium is the origin of sodium ions which appeared in the renal venous plasma during acute renal vein congestion.