[Effects of angiotensin II on the cerebral circulation and function]

The effect of angiotensin II (A II) on cerebral arteries is variable; A II would constrict or dilate cerebral arteries depending on species, the size of vessels examined, preexisting contractile levels, and the presence of functional endothelium. Hence exogenously applied A II may increase or decrease cerebral blood flow. The physiological role played by endogenous A II is even unclear in the cerebral circulation. Endogenous A II is unlikely to modulate cerebral blood flow. However, it may play some roles in the determination of the autoregulation of cerebral blood flow, at least judging from the effect of angiotensin converting enzyme inhibitors. Circulating A II elevates blood pressure, and promotes water and sodium intake. A II derived from the central renin-angiotensin system would play diverse roles as a neurotransmitter or a local hormone.