Effect of central administration of angiotensin II on cerebrospinal fluid formation in rabbits

The effect of central administration of AII on CSF formation was studied in alpha-chloralose and urethane anesthetized rabbits using the ventriculocisternal perfusion method. AII infused i.c.v. at rates of 5.5 and 55 pg/min significantly decreased CSF production by 25% and 35%, respectively. In contrast, AII when given at 5.5 ng/min did not change CSF formation. It seems that drop in CSF production observed during central administration of AII at low doses is mediated by both increased vasopressin release and activation of the sympathetic nervous system. The lack of changes in CSF formation with the highest AII dose used is not clear at present and awaits further investigation. Specific AII antagonist, saralasin, was found to significantly increase CSF production in four of five animals studied. It is suggested that in normal conditions AII may exert a tonic inhibitory effect on CSF formation.