Figure 1.

Key components of the angiotensin (Ang) system relevant to the blood–brain barrier. The traditional arm of the system (shown in yellow) consists of the sequential processing of Ang I, Ang II, and Ang III. The latter two act upon the AT1 receptor to cause a number of physiological actions, including (for the most part) vasoconstriction, increased oxidative stress, and inflammation. The AT2 receptor may contribute as well to oxidative and inflammatory signaling, but may oppose vasoconstriction. In recent years, evidence has been found for a parallel arm (shown in green) that largely opposes the traditional actions of Ang II/Ang III. The primary effector of this system is Ang(1–7), which acts through the Mas receptor. Both Ang(1–9) and Ang(1–7) may also act through AT2R. Abbreviations: ACE, angiotensin-converting enzyme; ACE2, angiotensin-converting enzyme 2; AP, aminopeptidase; CP, carboxypeptidase; NEP, neutral endopeptidase.