Relationships Among Intravascular Volume, Total Body Sodium, Arterial Pressure, and Vasomotor Tone
In rats made hyponatremic, hypovolemic, and hypotensive by intraperitoneal injections of 5 per cent glucose solution, arterial pressure was returned to control values by correction of the intravascular-volume deficit with either 5 per cent salt-free albumin or small volumes of hypertonic sodium-chloride solution. In the former, severe hyponatremia persisted; in the latter, it was corrected. Isotonic sodium-chloride solution, given in amounts considered sufficient to repair the extracellular-fluid and electrolyte deficits, was not so effective either in controlling hypotension or in expanding the intravascular volume. Using the height of the norepinephrine pressor response and the duration of the serotonin depressor phase as estimates of sympathetic activity, sympathetic vasomotor tone was found to be enhanced during hyponatremic, hypovolemic hypotension and depressed by administration of 5 per cent albumin, hypertonic and isotonic sodium-chloride solutions. These changes in estimates of sympathetic activity seemed dependent on changes in intravascular volume and not in extracellular sodium concentrations. Experiments performed following pentolinium-induced ganglion blockade showed that the depressor phase of the serotonin response was dependent on sympathetic vasomotor outflow, but that the height of norepinephrine pressor response was dependent not only on sympathetic activity, but also on the intravascular volume. In this study of selective sodium deficit, intravascular volume was found to be an important determinant of arterial pressure and sympathetic vasomotor tone.
- Received May 25, 1961.
- © 1961 American Heart Association, Inc.