BRAIN ANGIOTENSIN AND CIRCULATORY CONTROL

1. Components of the renin-angiotensin system (RAS) are found in the b rain; both outside and inside the blood-brain barrier. 2. Almost all o f the classical actions of the brain RAS are attributable to angiotens in (Ang) II and mediated by AT(1) receptors. 3. Circumventricular orga ns (CVO), which lack the blood-brain barrier, are rich in AngII recept ors and monitor circulating AngII levels, In vivo binding studies sugg est that the CVO are also accessible to cerebrospinal fluid-derived An gII. 4. The median preoptic nucleus, paraventricular hypothalamic nucl eus, supraoptic nucleus, nucleus tractus solitarius and ventrolateral medulla are inside the blood-brain barrier and are sites of action of brain AngII, In these nuclei, AngII seems to act as an excitatory neur otransmitter or neuromodulator. 5. Actions of AngII in the brain, both inside and outside the blood-brain barrier, are implicated in the cen tral regulation of blood pressure and sympathetic outflow, release of hypothalamic and pituitary hormones and renal sodium handling. 6. Alte rations in the activity of brain AngII may be involved in the mechanis ms of some types of hypertension.