The brain renin-angiotensin system: a critical analysis.

The concept of a brain renin-angiotensin system originated with the observation that the components necessary for the formation of angiotensin II are present in the central nervous system. This observation has been confirmed and extended, and it is now frequently assumed that there is a functional brain renin-angiotensin system. However, careful analysis of the available evidence has revealed a number of significant problems. It appears that most of the renin-like activity measured in extracts of brain is due to the acid protease cathepsin D; this is unlikely to function as an angiotensin-forming enzyme in vivo. Experiments involving central administration of renin substrate have not provided convincing evidence for a significant renin-renin substrate interaction in vivo. Attempts to demonstrate the presence of angiotensin in the brain have been plagued with problems of specificity and it is still not clear if the peptide is actually present in the central nervous system. These problems do not rule out the possibility that there is a brain renin-angiotensin system, but more definitive evidence is required before it can be concluded that such a tensin system exists.