Physiology and

The RAAS is an enzyme cascade that

Figure 7.1 details the principal steps in the

cascade and indicates the points at which it

can be inhibited. Angiotensin II has long been

known to mediate vasoconstriction, promote

sodium retention and stimulate aldosterone

release. Aldosterone may also be considered an

effector hormone of the RAAS.2 Angiotensin

II promotes sodium and water retention and

is crucial in the regulation of peripheral

resistance. It has been shown to promote the

proliferation of a variety of cell types,

including vascular smooth muscle cells,

fibroblasts and mesangial cells, and to

stimulate the deposition of extracellular

matrix in a number of tissues, including the

heart.3-5 These effects are frequently mediated

in a paracrine fashion through the action of a

The components of the RAAS are found in

tissues as well as the circulation. However, the

relative importance of the systemic and tissue

systems is not yet clear.