The renin angiotensin system--its physiology and role in disease states.

The renin-angiotensin system is one of a number of interlinked mechanisms regulating vascular resistance and blood volume. Under certain conditions it may become a predominant factor in maintaining vascular tone. Knowledge about these conditions (sodium depletion, mineralocorticoid deficiency, renovascular hypertension and iatrogenic hyperreninaemic states) is important for the safe and effective use of drugs which inhibit the renin-angiotensin system. Measurements of plasma renin activity are useful in the diagnostic assessment of hypertensive patients with hypokalaemia or evidence of renal artery stenosis. They may also have a place in the management of refractory or dialysis-resistant hypertension. Their use in the selection of antihypertensive therapy for the individual patient is controversial. Sequential measurements of plasma renin are helpful in analysing states of electrolyte depletion, and in titrating therapy for Addison's disease.