Localization of components of the renin-angiotensin system and site of action of inhibitors.

The renin-angiotensin system plays an important role in the regulation of blood pressure and fluid and electrolyte homeostasis. Components of this system, renin, angiotensin converting enzyme (ACE) angiotensinogen, angiotensin II and angiotensin II receptors have been found in many tissues including kidney, adrenal, blood vessels and in discrete brain regions. This suggests that in addition to circulating angiotensin II, endogenous tissue renin-angiotensin system may also be important in cardiovascular control and maintaining fluid balance. Inhibitors for ACE are used successfully in the treatment of hypertension and chronic heart failure. In experimental animals, these inhibitors are found to block ACE in the kidney, lung, adrenal, blood vessels and the forebrain circumventricular organs after oral administration. The time course of tissue ACE inhibition correlated closely with the blood pressure lowering effect of these drugs. Most ACE inhibitors are unable to penetrate the blood-brain and blood-testis barriers. However, the more lipophilic drugs do penetrate the blood brain barrier, especially after chronic administration. The potential use of inhibitors for renin and angiotensin II receptors for the treatment of hypertension are being explored. An inhibitor for the AT1 angiotensin receptor, losartan (CAS 124750-99-8), which has potent antihypertensive effect, demonstrated dose and time dependent inhibition of AT1 receptors in the kidney and adrenal. Losartan also crossed the blood-brain barrier after acute peripheral administration suggesting additional possible central sites of action.