Effect of intravenous and intracerebroventricular infusion of hypertonic solutions on plasma and cerebrospinal fluid vasopressin concentrations.

In the anesthetized dog, intravenous infusion of 2.5 M saline (40 microliters/kg . min) increased plasma and cerebrospinal fluid (CSF) osmolality and the plasma vasopressin (ADH) concentration, but did not increase the CSF ADH concentration. The increase in the plasma ADH concentration coincided with the increase in plasma osmolality, but preceded the increase in CSF osmolality. Intracerebroventricular infusion of hypertonic artificial CSF (2,000 mosm/kg . H2O, 10 microliters/min) increased CSF osmolality and plasma CSF ADH concentrations; plasma osmolality did not increase. Thus, receptors which sense changes in plasma osmolality appear to be outside the blood-brain barrier; different receptors may sense changes in CSF osmolality.