[From the circulating renin-angiotensin system to the intratissular renin-angiotensin systems. A complex relationship...

Since renin angiotensin (RA) system discovery during 1930 decade, its physiopathological importance was only recently demonstrated with the dramatic therapeutic value of angiotensin converting enzyme (ACE) inhibitors. The tissular localisation of some of its compounds progressively lead to the concept of a tissular RA system. However non consensus can be established concerning either its existence or its physiological role. The distribution of the classical components of the RA system in the cardiac and other tissues is not homogenous enough to demonstrate the existence of such a functional and coherent system. Numerous technical problems concerning dosage methodologies are encountered especially with angiotensin II determination and must rend cautious when interpreting data. Non specific actions of ACE inhibitors can explain discrepancies between their effects and the level of RA system activation. Indeed they interfere with other systems such as prostaglandins, leucotriens, bradykinins, free radicals. Different tissues such as those of the cardiovascular system directly interfere with angiotensin II production. However, mechanisms and enzymatic reactions that are involved in such a production are multiple and their respective roles remain to be determined.