The renin-angiotensin system: importance in physiology and pathology.

In recent years, the role of the renin-angiotensin system (RAS) in the development of hypertension has been investigated extensively. Studies have shown that there are actually two systems: a tissue and a circulating RAS. The control of hypertension is focused primarily in the RAS in the cardiovascular system and the brain. By manipulating the RAS with angiotensin converting enzyme (ACE) inhibitors, researchers have learned that the cardiovascular neuronal centers in the brain have receptor sites for the actions of angiotensin II (Ang II). Receptors for Ang II are found in the medulla oblongata in neurons involved in the regulation of baroceptor activity. Since studies in both animals and hypertensive patients indicate that ACE inhibitors reduced sympathetic activity and enhanced baroceptor sensitivity, it is possible that the primary hypotensive mechanism of these agents is through blockage of Ang II formation in the cardiovascular centers of the brain.