Discussion 3: Antihypertensive Drugs

Antihypertensive Drugs
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1 Briefly describe the therapeutic actions of drugs affecting blood pressure (diuretics, ACE inhibitors, ARBs, CCB, sympathetic nervous system drugs).
Diuretics
Parker et al. (2015) explained that diuretics improve the release of sodium from the kidneys. As a result, the water is excreted along with the solute. Typically, only 1.5 of 180 liters of water filtered by the kidneys are excreted in the urine. Diuretics increase this volume to reduce the overall circulating fluid. The different types of diuretics have distinguished sites and mechanisms of action.
Angiotensin-Converting Enzyme (ACE) Inhibitors
Angiotensin II functions to prevent the reuptake of noradrenaline, excite the cells that discharge catecholamines from suprarenal glands, diminish the release of sodium and water in the urine, enhance the production and release of aldosterone, and enhance the hypertrophy of smooth muscles in the blood vessels and cardiac muscle cells. These make angiotensin II a potent vasoconstrictor that mainly affects the precapillary arterioles and postcapillary venules, increasing blood pressure. ACE inhibitors prevent angiotensin II production by blocking the ACE action, which converts angiotensin I to angiotensin II (Herman et al., 2021).
Its lack of production leads to the overall decrease in blood pressure by promoting natriuresis, decreasing cardiac preload and afterload. Furthermore, it helps alleviate the progression of cardiovascular diseases by slowing down cardiac myocyte and smooth muscle remodeling (Herman et al., 2021).
Angiotensin Receptor Blockers (ARBs)
In normal conditions, the AT1 receptors are activated by the action of angiotensin II, leading to the contraction of smooth muscles in the blood vessels, enhanced sympathetic activity, improved systemic vascular resistance, and water retention secondary to the amplified reabsorption of sodium at the proximal convoluted tubule (PCT). These mechanisms increase blood pressure. ARBs, also known as angiotensin II receptor antagonists, works to inhibit the action of angiotensin 1 (AT1) receptors, to prevent the action of angiotensin II, which is a potent vasoconstrictor (Ahad et al., 2016).
Calcium Channel Blockers (CCBs)
CCBs decrease blood pressure by inhibiting extracellular calcium entry into the cardiac cells and vascular smooth muscle cells. Calcium aids in the contraction of these cells, especially the cardiac myocytes, and helps prolong depolarization before repolarization occurs. There are two types of CCBs. First, the dihydropyridines (i.e., amlodipine, clevidipine, nicardipine) dilates the arterial vasculature to reduce blood pressure. Second, the non-dihydropyridines (i.e., verapamil, diltiazem) decrease cardiac contractility and rate and induce minimal arterial dilation. Therefore, blocking the action of calcium reduces cardiac contractility, thereby diminishing blood pressure (Lin & Ma, 2018; Mayo Clinic, 2019).
Sympathetic Nervous System Drugs
Drugs that affect the sympathetic nervous system include beta-adrenoreceptor and Alpha-adrenoreceptor antag...