THE ROLE OF ANGIOTENSIN-II IN THE REGULATION OF BLOOD-FLOW TO CHOROIDPLEXUSES AND CEREBROSPINAL-FLUID FORMATION IN THE RAT

The effect of peripherally administered angiotensin II (AII) on blood flow to choroid plexuses was examined in pentobarbital-anesthetized ra ts. The indicator fractionation method with I-123- or I-125-N-isopropy l-p- iodoamphetamine as the marker was employed to measure blood flow. Basal blood flow to choroid plexus of the lateral cerebral ventricle (LVCP) (3.19 +/- 0.23 ml g(-1) min(-1)) was lower than that to choroid plexuses of the third (3VCP) and fourth (4VCP) ventricles (3.90 +/- 0 .38 and 3.95 +/- 0.36 ml g(-1) min(-1), respectively). The effect of A II on choroidal blood flow varied depending on peptide dose and anatom ical location of the choroidal tissue. AII infused intravenously at ra tes of 30 and 50 ng kg(-1) min(-1) decreased blood flow to both LVCP a nd 4VCP by 12-20%. Both lower (10 ng kg(-1) min(-1)) and higher (100 a nd 300 ng kg(-1) min(-1)) AII doses did not alter blood flow to LVCP a nd 4VCP. Blood flow to the 3VCP was not affected by any dose of the pe ptide used. In comparison, blood flow to cerebral cortex increased by 33% during intravenous AII infusion at a rate of 300 ng kg(-1) min(-1) . The choroidal blood flow-lowering effect of moderate AII doses was a bolished by both AT(1) (losartan) and AT(2) (PD 123319) receptor subty pe antagonists (3 mg kg(-1) i.v.). To determine whether the hemodynami c changes observed in choroid plexuses with moderate AII doses influen ce CSF formation, the ventriculocisternal perfusion was performed in r ats (under the experimental conditions described) with Blue Dextran 20 00 as the indicator. CSF production was not altered during intravenous infusion of AII at a rate of 30 ng kg(-1) min(-1). It is suggested th at CSF formation is maintained in pathophysiological situations accomp anied by increased plasma AII levels, which implicates a potential rol e for AII in regulating ion and water balance in the CNS.