[Role of brain angiotensin II system in subfornical organ-pressor responses]

We studied the role of brain angiotensin II in subfornical organ-pressor responses using urethane-anesthetized, tubocurarine-immobilized rats, and the present work obtained the following findings: (1) angiotensin II (A II) induced pressor responses by injection into several brain regions: either subfornical organ (SFO),nucleus paraventricularis (NPV) or its projection areas, including rostral ventrolateral medulla (RVLM),periaqueductal gray matter (PAG) and locus coeruleus (LC); (2) SFO pressor responses were markedly attenuated by preinjection of [Sar(1),Thr(8)]-A II (ST-A II, an A II antagonist) into bilateral NPV or RVLM,while NPV pressor responses were suppressed by ST-A II injection into the RVLM; (3) both SFO- and NPV-pressor responses were decreased by ST-A II preinjection into bilateral PAGL; and (4) ST-A II preinjection into bilateral LC could only attenuate NPV pressor responses without affecting SFO pressor responses. Taken together with our previous findings that the RVLM mediates the pressor responses of the PAG and LC, the present results indicate that A II activates A II ergic neurons in the SFO may evoke pressor responses by acting upon RVLM through NPV and NPV- PAG -RVLM system. Whereas NPV- LC- RVLM system was not involved in the SFO pressor responses.