LOCAL RENIN-ANGIOTENSIN SYSTEMS IN CARDIOVASCULAR TISSUES - LOCALIZATION AND FUNCTIONAL-ROLE

In its classical definition, the renin-angiotensin system (RAS) acts p redominantly by endocrine mechanisms. This view has been modified sinc e several components of the RAS and their mRNAs were found in peripher al tissues. These findings gave rise to the concept of local tissue re nin-angiotensin systems. Although no cells of cardiovascular organs co ntaining a complete RAS have been identified as of this writing, angio tensinogen and angiotensin-converting enzyme (ACE) are most likely syn thesized within the vasculature for example. Local synthesis of renin may be limited to very small amounts, but uptake of renin from the cir culation is very likely. The function of local RASs is shown by reduct ion of blood pressure by ACE inhibitors, which correlates better with the inhibition of ACE activity in certain tissues than with its activi ty in the plasma. Further studies have put forward the notion that the circulating RAS could mainly be important for acute hemodynamic stabi lity, whereas the tissue RAS could be involved in more long term maint enance of hemodynamics. This review will try to summarize the findings leading to the concept of a local tissue renin-angiotensin system, an d discuss interactions between the circulating and the local RAS in th e light of recent experimental findings.