The renin-angiotensin system because of its unique relationship to both aldosterone secretion and vascular reactivity is important in the control of blood pressure and may be useful in determining the cause of hypertension. 2. Patients with volume expanded hypertension almost invariably have low renin levels. Some of these patients have primary aldosteronism, others have excess production of nonaldosterone mineralocorticoids. The majority have essential hypertension. 3. Many patients with low renin essential hypertension have an enhanced adrenal response to angiotensin II as the underlying mechanism. 4. Fifteen to twenty per cent of patients with an elevated blood pressure have renin-dependent angiotensinogenic hypertension. Some of these patients have renal lesions to account for the elevated renin levels, for example, renal artery stenosis. However, some patients with high renin essential hypertension have a decreased adrenal response to angiotensin II as the primary mechanism for their high renin levels and potentially for their elevated blood pressure. 5. Patients who fall into this latter group may not only have alterations in angiotensin's interaction with the adrenal but also with other target tissues, for example, renal vasculature. 6. Thus, as many as 60% of patients with essential hypertension may have an alteration in the interaction of angiotensin II with its target tissues which could be the major factor underlying the pathogenesis of their elevated blood pressure.
