Effect of arginine vasopressin on CSF composition and bulk flow in hyperosmolar state

To find out whether central arginine vasopressin (AVP) plays a role in regulation of cerebrospinal fluid (CSF) composition and of CSF bulk flow (CSFbf) in acute hyperosmolar state, the experiments were performed on 16 anesthetized cats in which the ventriculocisternal system was perfused either with artificial CSF (aCSF; 8 control experiments) or with aCSF containing AVP (10 microU/min, 8 experiments) before, during, and after intravenous infusion of 5% NaCl. In both series, hyperosmotic infusion significantly increased CSF osmolality (CSFosmol) and sodium (CSFNa) and potassium (CSFK) concentration and reduced CSFbf. Administration of AVP significantly influenced the dynamics of changes in CSFNa and slightly affected changes in CSFK concentration induced by infusion of hyperosmotic saline, while it did not modify changes in CSFosmol) and CSFbf. In control experiments, CSFbf was significantly related to plasma and CSF osmolalities and sodium concentrations, whereas in AVP experiments these relationships were markedly suppressed. The results suggest that during acute hyperosmolar state AVP significantly influences sodium handling in CSF and may play a role in adaptation of the brain to hyperosmolality.