Hypertension Pathophysiology & Drug Mechanisms
Understanding the pathophysiological mechanisms underlying hypertension clarifies why specific drug classes are preferred in specific settings. Each mechanism described here maps directly to the drug selection recommendations in the 2025 AHA/ACC guideline.
Renin-Angiotensin-Aldosterone System (RAAS)
Most targeted pathway in hypertension pharmacology
Mechanism
Renin cleaves angiotensinogen to angiotensin I, converted by ACE to angiotensin II (Ang II). Ang II binds AT1 receptors causing potent vasoconstriction, aldosterone release (Na+ retention), sympathetic activation, and vascular remodeling. Overactivation drives sustained hypertension through volume expansion and increased peripheral resistance.
Drug Targets
ACE Inhibitors (ACEi)
Block ACE, reducing Ang II formation. Reduce vasoconstriction, aldosterone secretion, and sympathetic activation. Additional benefit via bradykinin accumulation (vasodilation) — but also causes cough (bradykinin effect).
Angiotensin Receptor Blockers (ARBs)
Block AT1 receptor directly. Same BP-lowering efficacy as ACEi without bradykinin-mediated cough. Allow AT2 receptor stimulation (potentially cardioprotective).
Mineralocorticoid Receptor Antagonists (MRA)
Spironolactone and eplerenone block aldosterone at its receptor. Reduce Na+ retention, K+ excretion, and vascular fibrosis. Key role in resistant HTN where aldosterone excess is common.
Direct Renin Inhibitors (aliskiren)
Block renin activity at the first step of the cascade. Limited clinical use; not first-line in current guidelines.
Key Clinical Points
- ACEi and ARBs reduce proteinuria independently of BP — preferred in CKD and diabetic nephropathy
- RAAS blockade reduces LV hypertrophy and vascular remodeling beyond BP effects
- ACEi/ARB combination provides no additional benefit and increases adverse events — avoid
- Hyperkalemia risk with RAAS blockade — monitor K+ and eGFR, particularly in CKD
Sympathetic Nervous System (SNS) Activation
Neurogenic component of hypertension
Mechanism
Increased sympathetic tone raises BP through: (1) increased heart rate and cardiac output via beta-1 stimulation, (2) vasoconstriction via alpha-1 stimulation, (3) renin release from juxtaglomerular cells via beta-1 stimulation, and (4) renal sodium reabsorption. SNS hyperactivity is common in obesity, sleep apnea, and stress-related HTN.
Drug Targets
Beta-blockers
Block beta-1 adrenoreceptors: reduce heart rate, cardiac output, and renin release. Carvedilol additionally blocks alpha-1 (vasodilation). Preferred in HTN with CAD, HFrEF, or tachyarrhythmias. Not first-line for uncomplicated HTN in 2025 guideline.
Alpha-1 blockers (doxazosin, prazosin)
Block post-synaptic alpha-1 receptors, causing arterial and venous vasodilation. Used in resistant HTN (Module 6). Risk of orthostatic hypotension with first dose.
Central alpha-2 agonists (clonidine, methyldopa)
Stimulate central alpha-2 receptors, reducing sympathetic outflow. Methyldopa is preferred in pregnancy. Clonidine has rebound HTN risk upon abrupt discontinuation.
Key Clinical Points
- Beta-blockers are second-line for uncomplicated HTN — first-line for HTN + CAD, HFrEF, or rate control needs
- Rebound hypertension occurs with abrupt beta-blocker or clonidine discontinuation — taper gradually
- Carvedilol and labetalol have combined alpha/beta blockade — preferred in certain settings (HF, cocaine-induced HTN)
- Sleep apnea treatment reduces SNS activation and lowers BP — address underlying causes
Endothelial Dysfunction & Nitric Oxide Deficiency
Vascular biology of hypertension
Mechanism
The endothelium regulates vascular tone via nitric oxide (NO) release from eNOS. Hypertension reduces NO bioavailability through oxidative stress (ROS inactivating NO), inflammation, and shear stress dysregulation. Reduced NO → impaired vasodilation, increased platelet aggregation, leukocyte adhesion, and vascular remodeling. Endothelial dysfunction is both a cause and consequence of hypertension.
Drug Targets
Calcium Channel Blockers (CCB) — Dihydropyridines
Amlodipine, nifedipine: block L-type Ca2+ channels in vascular smooth muscle, causing vasodilation. Also improve endothelial function through NO-independent mechanisms. Preferred in ISH and elderly patients.
Calcium Channel Blockers — Non-dihydropyridines
Verapamil, diltiazem: block cardiac and vascular Ca2+ channels. Reduce HR and contractility (negative chronotrope/inotrope). Preferred when HTN coexists with AF or SVT.
ACEi/ARBs (via kinin pathway)
ACEi increase bradykinin → stimulate eNOS → increase NO production. This NO-dependent mechanism contributes to endothelial restoration beyond BP lowering.
Key Clinical Points
- Dihydropyridine CCBs (amlodipine) are first-line for isolated systolic hypertension and elderly patients
- Non-DHP CCBs (verapamil, diltiazem) are contraindicated with beta-blockers — risk of complete heart block
- CCBs are preferred in Black patients (low renin hypertension responds better to vasodilators than RAAS blockade)
- Amlodipine has exceptionally long half-life (35–50 hours) — once-daily dosing sufficient, less BP variability
Renal Sodium Retention & Volume Expansion
Renal contribution to blood pressure regulation
Mechanism
The kidney regulates BP through pressure-natriuresis: as BP rises, Na+ and water excretion increase to restore equilibrium. In HTN, this set-point is reset — higher BP required to achieve normal natriuresis. Mechanisms include: overactive RAAS/aldosterone, SNS activation of renal tubules, intrinsic tubular abnormalities. Result: chronic volume expansion and sustained elevated BP.
Drug Targets
Thiazide/Thiazide-like Diuretics
Chlorthalidone, indapamide, hydrochlorothiazide: block Na+-Cl- cotransporter in distal convoluted tubule. Initial effect: volume depletion. Long-term: vasodilation. Chlorthalidone preferred (3× longer half-life, better outcomes data).
Loop Diuretics (furosemide, torsemide)
Block Na+-K+-2Cl- transporter in thick ascending limb. Potent natriuresis — preferred in HTN with fluid overload, advanced CKD (eGFR <30), or HF. Not first-line for HTN without compelling indication.
MRA (spironolactone, eplerenone)
Block aldosterone-mediated Na+ reabsorption in collecting duct. Potassium-sparing. Essential in resistant HTN — most patients have relative aldosterone excess.
Key Clinical Points
- Chlorthalidone is preferred over HCTZ — 3× longer half-life, more consistent 24-hour BP control, better outcomes data (ALLHAT)
- Thiazide diuretics worsen hyperuricemia, hypokalemia, and glucose tolerance — monitor electrolytes and uric acid
- Low-dose chlorthalidone (12.5 mg) often sufficient with less metabolic side effects
- ALLHAT trial: chlorthalidone equal to amlodipine and lisinopril for CV outcomes in high-risk patients
Arterial Stiffness & Isolated Systolic Hypertension
Vascular aging and pulse pressure physiology
Mechanism
With aging, arterial elastin degrades and collagen crosslinks accumulate, increasing aortic stiffness. Stiff vessels: (1) reflect pulse wave earlier (arriving during systole instead of diastole), (2) augment systolic pressure, (3) reduce diastolic pressure, widening pulse pressure. Result: isolated systolic hypertension (ISH) — high SBP with normal or low DBP. Common in elderly; associated with increased CV risk beyond mean arterial pressure.
Drug Targets
Long-acting Dihydropyridine CCBs (amlodipine)
Most effective at reducing pulse wave velocity and SBP in ISH. Vasodilate peripheral arteries, reducing reflected wave augmentation.
Thiazide-like Diuretics
Reduce total body sodium and arterial wall sodium content, improving arterial compliance. Effective for ISH.
Low-dose ACEi/ARBs
Reduce aldosterone-mediated arterial fibrosis and vascular stiffness. Less effective than CCBs at reducing pulse wave velocity acutely but beneficial long-term.
Key Clinical Points
- Isolated systolic hypertension (SBP ≥130, DBP <80) is the dominant hypertension phenotype in adults >60 years
- Treating ISH reduces CV events — SPRINT and STEP demonstrated benefit in older patients
- Be cautious lowering DBP too much in elderly — diastolic BP <60–65 mmHg may reduce coronary perfusion (J-curve)
- Pulse pressure >60 mmHg is an independent predictor of CV risk beyond mean arterial pressure
Drug Class Summary: Mechanism vs. Indication
Quick reference for antihypertensive selection
Mechanism
First-line antihypertensive agents are selected based on mechanism, compelling indications, and contraindications. The 2025 AHA/ACC guideline recommends four drug classes as first-line: ACEi/ARB, dihydropyridine CCB, and thiazide-type diuretics. Combination therapy (SPC) is preferred over sequential monotherapy for most patients requiring >1 agent.
Drug Targets
First-line: ACEi/ARB
Block RAAS. Preferred: CKD, proteinuria, HFrEF, diabetes, post-MI. Avoid: bilateral renal artery stenosis, pregnancy, history of angioedema (ACEi).
First-line: DHP-CCB (amlodipine)
Vasodilate via Ca2+ channel block. Preferred: ISH, elderly, Black patients, angina. Avoid: HFrEF (negative inotrope effect of non-DHP only).
First-line: Thiazide-like diuretic (chlorthalidone)
Reduce volume via NCC blockade. Preferred: ISH, systolic HF, edema, Black patients. Avoid: gout (relative), severe hyponatremia.
Second-line: Beta-blocker
Reduce HR, CO, and renin. Preferred: CAD, HFrEF, AF, post-MI, migraine. Avoid: asthma/COPD (non-selective), decompensated HF.
Key Clinical Points
- Start with combination therapy (2 agents) for Stage 2 HTN or high-risk Stage 1 HTN — more effective than sequential monotherapy
- Single-pill combinations (SPC) improve adherence significantly vs free combinations — prefer SPC when available
- Black patients: lower response to ACEi/ARB monotherapy (low-renin HTN) — prefer CCB or thiazide as initial therapy
- Resistant HTN: add spironolactone as 4th-line agent (PATHWAY-2) — most have relative aldosterone excess
Mechanism summaries are based on the 2025 AHA/ACC Guideline for the Diagnosis and Management of Hypertension in Adults. Whelton PK, et al. Hypertension. 2025. doi:10.1161/HYP.0000000000000116