Quiz 31: Drugs Affecting the Renin-Angiotensin-Aldosterone System

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Lisinopril is a drug prescribed for the treatment of hypertension, heart failure, and acute myocardial infarction. They act by binding on to the angiotensin converting enzyme (ACE) thereby preventing the formation of Angiotensin II responsible for increasing the blood pressure. The less production of Angiotensin II reduces the secretion of aldosterone resulting in lower sodium and water retention by the kidneys thus lowering the blood volume and controlling the blood pressure. Spironolactone on the other hand inhibits aldosterone by binding to its receptors. The drug acts as a potent diuretic and induces mild diuresis. It also has no or less effect on excretion of potassium. The rate of morbidity, mortality, and dysrhythmias associated with heart failure has been shown to be reduced while using this drug. The earlier drug Lisinopril must be prescribed with care and the patient's medical history must be checked for other medical conditions. This is because the drug can cause serious dysrhythmias in case of renal impaired patients. As, E is middle aged women and she might have or develop other complications, it is therefore the drug spironolactone would have been prescribed to her.

The body maintains a homeostatic mechanism to maintain the blood pressure. An alteration in this mechanism can lead to either hypotension, which causes dizziness and less urine excretion or hypertension that may lead to rupture of blood vessels resulting in loss of blood to vital organs. The regulation of blood pressure is maintained by cluster of neurons located on the medulla oblongata called vasomotor center. The vasomotor center reacts to the information received from the baroreceptors and chemoreceptor's and regulates the pressure accordingly. The baroreceptor reflex plays an important role in regulating the blood pressure. If there is a raise in the pressure in the vascular system, the reflexes produced will constrict the arterioles and veins and thereby increase the heart rate. The drugs used for lowering the blood pressure can trigger the baroreceptor reflex and regulate blood pressure back to normal level. Due to this mechanism the patient may feel palpitations as a result of increased heart rate termed as reflex tachycardia.

Losartan (Cozaar) is a drug generally prescribed for the treatment of hypertension (HTN), stroke prophylaxis in patient with left ventricular hypertrophy and for the prevention of nephropathy in patients with type II diabetes. Losartan specifically blocks the AT 1 receptor of Angiotensin II thereby regulating the blood pressure. When the AT 1 receptors of Angiotensin II are blocked in the arteriolar smooth muscles, reduction in flow of blood from arteries reduces the blood pressure. The secretion of aldosterone is prevented when AT 1 receptors of Angiotensin II present in adrenal gland is blocked. The blocking of AT 1 receptors of Angiotensin II in the heart prevents cardiac remodeling and reduces the blood pressure.

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