1. Angiotensin Is a Powerful Hormone
The hormone angiotensin is secreted in the liver and acts directly at the kidney to raise blood pressure. The hormone is secreted in response to stimuli by other hormones in the body, and as a response to low blood pressure. Angiotensin must be converted from an inactive form to active. The active form of angiotensin has multiple cardiovascular effects--including vasoconstriction, which raises the blood pressure. It also has direct effects on the kidney and adrenal glands, which help the body hold onto fluid and salt in times of dehydration and low blood pressure (such as in a state of shock).
2. Angiotensin Converting Enzyme Mediates the Action of Angiotensin
Renin mediates the conversion of angiotensinogen to the active angiotensin. The angiotensin converting enzyme (ACE) is found all over the body, but is concentrated in the lungs and kidneys. his enzyme mediates further conversion of angiotensin to a more active form. There are enzymes available to break down angiotensin in the vessel walls.
3. ACE Inhibitors Reduce the Action Angiotensin
The ACE inhibitors are potent cardiovascular medications that prevent the ACE from converting angiotensin to more active molecules. The action is high in the angiotensin pathway, and thus results in a lowering of the blood pressure. The major side effect of the ACE inhibitors is cough. This is mediated by the buildup of bradykinin, which is a converting enzyme as well. The major side effect of ACE inhibitors is angio-edema (severe swelling of the face, lips and tongue, plus throat issues), which can be very serious if unrecognized and treated promptly. The various converting enzymes have some protective effect on the vasculature, and reduce blood pressure as well. The most widely used ACE inhibitors are captopril, enalapril, benazepril and ramipril.
4. ACE Inhibitors Have Indications Other Than Blood Pressure Lowering
ACE inhibitors are indicated to treat high blood pressure, particularly in patients with increased left ventricular size. They are not the first-line medications for patients with newly diagnosed hypertension, but are recommended in certain high-risk situations, such as blood-pressure treatment in patients with a history of stroke, heart attack or vascular disease (based on the landmark HOPE trial published in the New England Journal of Medicine). Subsequent work has shown other protective actions in a variety of indications. In patients with congestive heart failure, ACE inhibitors have been found to improve heart function and survival. Patients with significant kidney disease and diabetes also benefit from taking ACE inhibitors, as they reduce the progression to renal failure. After a heart attack, treatment with an ACE inhibitor is proven to reduce mortality
5. Direct Angiotensin Receptor Blockers
Because ACE inhibitors work at an early stage of angiotensin formation, they are very effective in reducing blood pressure, but other active enzymes not inhibited will bind to receptors, which can lead to hypertension. Furthermore, not all patients can tolerate the ACE inhibitors because of cough mediated by bradykinin. The angiotensin receptor blockers (ARBs) are an additional class of medications that are effective as blood-pressure medications. They do not cause cough, as their mechanism of action does not result in the production of bradykinin. They are widely marketed: Every pharmaceutical company sells an ARB. They have been extensively studiedm but only valsartan and candesartan have indications for treatment of heart failure and recent heart attack. Trials of both ACE inhibitors and ARBs have been shown to be associated with more adverse events, and the combination is not recommended.
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