Angiotensin receptor blockers are antihypertensive medicines used to treat high blood pressure. These medicines act as vasodilators to widen the blood vessels (vasodilation) and reduce blood pressure.
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What is angiotensin?
The term ‘angiotensin’ is used to collectively define a group of 4 peptide hormones (angiotensin I – IV) that are crucial for blood pressure regulation. They are part of the renin-angiotensin-aldosterone system.
The first step of angiotensin synthesis is the hepatic formation of angiotensinogen (an inactive precursor), which is initially converted into angiotensin I by renin, and next to angiotensin II by angiotensin-converting enzyme.
The renin-angiotensin-aldosterone system primarily comprises three vital biomolecules namely renin, angiotensin II, and aldosterone, which exert their effects on the kidney, lungs, vascular system, and brain.
The main function of the system is to regulate blood pressure and maintain fluid balance by increasing sodium and water retention and regulating vascular tone.
How angiotensin works?
Angiotensin, particularly angiotensin II, binds to angiotensin II receptors (type I and type II) and increase the blood pressure in many ways.
In the kidney, angiotensin II increases sodium reabsorption, which in turn results in increased blood osmolarity and elevated arterial blood pressure.
In the adrenal cortex, angiotensin II induces the secretion of a steroid hormone, aldosterone, which acts by increasing the reabsorption of sodium and excretion of potassium. The net effect is increased blood volume and osmolarity, leading to increased blood pressure.
In the systemic arterioles, binding of angiotensin II to its receptor leads to vasoconstriction, which in turn causes induction of peripheral resistance and systemic blood pressure.
In the brain, angiotensin II acts on the hypothalamus to induce thirst sensation and increase water intake. Moreover, it acts on the posterior pituitary gland to induce the release of antidiuretic hormone, or vasopressin, which in turn causes retention of water in the kidney and elevation of the blood volume.
Lastly, angiotensin II prevents baroreceptor-mediated regulation of the blood pressure by reducing the receptor sensitivity.
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What are angiotensin receptor blockers?
Angiotensin receptor blockers, or angiotensin II receptor antagonists, are used to treat high blood pressure, heart failure, chronic kidney diseases, and diabetic nephropathy. They inhibit the action of angiotensin II by blocking the ligand-receptor interaction.
In simple words, angiotensin receptor blockers dilate or widen the blood vessel so that the blood can flow easily through the circulation. Also, they regulate blood volume by reducing sodium and water retention.
Angiotensin receptor blockers are particularly helpful when angiotensin II level is too much elevated in the body. Too high angiotensin II levels can lead to excessive fluid retention, sustained increase in blood pressure, and expansion of the heart, which may altogether cause heart failure.
However, too low angiotensin II can be detrimental as well. It can lead to abnormal blood volume regulation, increased potassium retention, and excessive loss of sodium and water, which altogether can cause significantly low blood pressure.
What are the side-effects of angiotensin receptor blockers?
Angiotensin receptor blockers usually do not have side-effects. Some people, however, can develop mild side-effects due to consumption of new medicine, or due to having a higher dose of the medicine.
The most common side-effects include dizziness, headache, fatigue, flu-like symptoms, higher blood potassium level, or skin swelling due to fluid accumulation (angioedema).
In some rare cases, the blockers can cause severe diarrhea and loss of body weight. These symptoms call for immediate medical attention.
Women who are pregnant, or planning to become pregnant, should not take these blockers because of the possible harmful effects on fetal development.
Do angiotensin receptor blockers react with other medicines?
It is not recommended to take the blockers along with angiotensin-converting enzyme inhibitors. Taking both the medicines together can lead to very high blood potassium level, which can further increase the risk of acute kidney injury and heart rhythm abnormalities.
In addition, certain painkillers and mild potassium-sparing diuretics can increase the risk of high blood potassium level, if taken together with the blockers.
For better results, people consuming angiotensin receptor blockers should limit their salt intake. Also, too much alcohol consumption can increase blood pressure and reduce the efficacy of the blockers.
What are the benefits of angiotensin receptor blockers?
Angiotensin receptor blockers have several benefits. In addition to reducing the risk of cardiovascular and kidney disorders, these blockers prevent organ damage and comorbidities caused by high blood pressure. The comorbid conditions that get maximum benefits from angiotensin receptor blockers include diabetes, microalbuminuria, and left ventricular dysfunction.
Most importantly, the blockers inhibit the functions of angiotensin II by directly blocking the receptor. This is more advantageous than reducing the level of angiotensin II in the body.
Moreover, studies have shown that the adherence to angiotensin receptor blocker-mediated therapies is higher than that observed in other antihypertensive medicines. Good treatment adherence is associated with better management of blood pressure.