CHANGES IN COCHLEAR BLOOD-FLOW DUE TO INTRAARTERIAL INFUSIONS OF ANGIOTENSIN-II(3-8) (ANGIOTENSIN-IV) IN GUINEA-PIGS

The effects of a newly discovered form of angiotensin, angiotensin IV (ANGIV), on cochlear blood flow (CBF) have been investigated utilizing the laser Doppler flowmetry (LDF) technique. Two specific questions w ere addressed: What are the effects of anterior inferior cerebellar ar tery infusions (AICA) of ANGIV on CBF and do angiotensin fragments oth er than ANGIV influence CBF in mature male and female guinea pigs. Inf usions of ANGIV, and C-terminal shortened fragments were accomplished via micropipette into the AICA and changes in CBF were observed using LDF. The results demonstrated that 10 and 100 pmol/min doses of ANGIV increased CBF 22% and 75% (n=6; P<0.01) from baseline, respectively, w ith little change in mean arterial blood pressure (MAP). Pretreatment with the ANGIV antagonist divalanal-ANGIV (1 nmole/min) blocked increa ses in CBF due to infusions of 100 pmol/min of ANGIV. The infusion of the C-terminal shortened fragment ANGIV(1-5) and saline had no signifi cant effect on either CBF or MAP. These results provide the evidence f or a new subtype of the angiotensin receptor and indicate the likely r ole of circulating hormones in blood flow regulation in the inner ear. (C) 1998 Published by Elsevier Science B.V.