REN and neurodegenerative disease: Two renin-angiotensin systems (RAS) exist in the brain, the systemic and the localRAS.205,206 However, since the BBB restricts the access of thesystemic RAS components to most brain regions, the brain RAS is probably essential in thepathophysiology of several neurodegenerative diseases.207–209 Thebrain RAS plays also an important role in regulating autonomic functions and maintainingcardiovascular homeostasis.210The enzyme renin initiates the RAS pathway by producing angiotensin I (Ang I) through thecleavage of angiotensinogen.