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Pathophysiology

TL;DR — There is no single mechanism of primary hypertension; there is a small set of systems that can each shift the operating point of the same regulated variable, and the genetics say the kidney is where the shift is decided. Every monogenic form of human hypertension so far identified alters renal salt handling — through the epithelial sodium channel, the mineralocorticoid pathway, or the WNK kinase network that controls the thiazide-sensitive cotransporter (Lifton 2001, PMID 11239411). The Guytonian claim that follows — that sustained hypertension requires a rightward shift in the kidney's pressure-natriuresis relationship (Guyton 1980, PMID 6994602; Hall 1986, PMID 3536587) — is standard but actively contested on logical and modelling grounds (Kurtz 2016, PMID 28637271; Osborn 2009, PMID 19286640; Evans 2016, PMID 26582636). Layered on renal sodium handling are sympathetic overactivity, renin-angiotensin-aldosterone signalling, large-artery stiffening that converts a flow disorder into a pressure disorder with age (Vasan 2022, PMID 35168368), adaptive immune activation (Caillon 2019, PMID 29952002), and — the most testable recent addition — tissue sodium storage outside the extracellular fluid compartment, which breaks the assumption that sodium balance is purely a renal affair (Titze 2014, PMID 24401786; Kopp 2013, PMID 23339169).

The regulated variable and the operating point

Arterial pressure is short-term-regulated by the baroreflex and long-term-regulated by whatever sets the relationship between pressure and sodium excretion. In the Guytonian formulation, because renal sodium output must equal intake at steady state, the only way to sustain a higher mean pressure indefinitely is to shift the pressure-natriuresis curve; every other perturbation is transient (Guyton 1980, PMID 6994602; Hall 1986, PMID 3536587; Brands 2012, PMID 23720255). This has been the field's organising idea for five decades and remains the standard account (Montani 2009, PMID 19286638).

It is also disputed. Critics argue that the infinite-gain property of the model is an artefact of how the equations are posed rather than a fact about kidneys, that whole-body autoregulation is not required to explain the data, and that the nervous system's long-term contribution is under-weighted in computational implementations (Kurtz 2016, PMID 28637271; Osborn 2009, PMID 19286640; Beard 2013, PMID 24555102). A "neo-Guytonian" position keeps the renal centrality but allows neural and vascular determinants a long-term role (Evans 2016, PMID 26582636). This is a genuine unresolved argument about the foundation of the field, not a historical footnote.

Renal sodium handling — the mechanism the genetics points at

Disorder Gene/pathway Effect
Liddle syndrome SCNN1B/G PY-motif mutations preventing Nedd4-2-mediated ENaC retrieval Constitutive ENaC activity, sodium retention, suppressed renin and aldosterone (Schild 1996, PMID 8665845; Nesterov 2016, PMID 27170740)
Pseudohypoaldosteronism type II (Gordon syndrome) WNK1, WNK4, KLHL3, CUL3 Failure to degrade WNK kinases → NCC hyperactivity → salt-sensitive hypertension with hyperkalaemia; thiazide-responsive (Shibata 2013, PMID 23576762; O'Shaughnessy 2015, PMID 25503323)
Apparent mineralocorticoid excess, glucocorticoid-remediable aldosteronism, others Mineralocorticoid pathway Inappropriate mineralocorticoid receptor activation (Lifton 2001, PMID 11239411)
Loss-of-function counterpart SLC12A1/NKCC2 rare variants Impaired transport, lower blood pressure — the mirror-image evidence (Monette 2011, PMID 21209010)

The WNK–SPAK/OSR1 network is regulated by angiotensin II through protein kinase C phosphorylation of KLHL3 and reversed by calcineurin, giving a molecular route by which the renin-angiotensin system tunes distal sodium reabsorption (Shibata 2014, PMID 25313067; Ishizawa 2019, PMID 30718414; San-Cristobal 2009, PMID 19240212), and the same kinases sense chloride to regulate NKCC2 (Ponce-Coria 2008, PMID 18550832; Kahle 2006, PMID 16990453).

Renin-angiotensin-aldosterone system

Angiotensin II raises pressure by vasoconstriction, sympathetic facilitation, aldosterone release and direct tubular sodium reabsorption; aldosterone acts on the mineralocorticoid receptor in the distal nephron and, importantly, elsewhere (te Riet 2015, PMID 25767283; Ames 2019, PMID 30806496). Mineralocorticoid receptor activation causes end-organ injury partly independent of pressure: in DOCA/salt mice, cardiac but not renal injury was mediated by endothelial mineralocorticoid receptors independently of blood pressure (Lother 2016, PMID 26553231), and brain mineralocorticoid receptors have their own hypertensive role (Gomez-Sanchez 2004, PMID 15202613). Dietary salt modifies aldosterone's organ toxicity (Catena 2013, PMID 23803228). This pressure-independent limb is the pharmacological rationale for mineralocorticoid receptor antagonists and, more recently, aldosterone synthase inhibitors (Verma 2024, PMID 38133623) — see pharmacological therapy.

That the same axis is quantitatively deranged in a large minority of ordinary hypertension is the most consequential recent finding in the field: renin-independent aldosterone production forms a continuum across the whole blood-pressure range, with biochemically overt primary aldosteronism in 11.3% of normotensive and 22.0% of resistant-hypertensive people (Brown 2020, PMID 32449886) — see secondary hypertension.

Sympathetic nervous system

Muscle sympathetic nerve activity and regional noradrenaline spillover are elevated in a substantial fraction of people with primary hypertension, particularly younger, obese and hyperkinetic phenotypes (Esler 2015, PMID 25680900; Esler 2000, PMID 11346214; Mancia 1997, PMID 9401621). Sympathetic transduction — how much pressure a given burst of nerve traffic generates — differs in untreated hypertension, so nerve traffic alone is not the whole story (Kobetic 2022, PMID 34453103). Baroreflex failure produces a distinctive labile hypertension that demonstrates the reflex's role by its absence (Heusser 2005, PMID 15837841). The clinical test of the sympathetic hypothesis has been renal denervation, whose history is covered in device and interventional therapy.

Vascular structure and arterial stiffness

With age, elastin fragmentation and collagen deposition stiffen the aorta, raising systolic and pulse pressure while diastolic pressure falls — which is why isolated systolic hypertension dominates after the sixth decade and why pulse pressure and diastolic pressure carry different prognostic information at different ages (Lewington 2002, PMID 12493255). In Framingham, arterial stiffness measured by carotid-femoral pulse wave velocity predicted a broad range of long-term outcomes (Vasan 2022, PMID 35168368), and its relative contribution versus hypertension itself has been formally partitioned (Niiranen 2016, PMID 27912210). Stiffness and hypertension are bidirectionally causal: parental hypertension predicts arterial stiffness in normotensive offspring (Andersson 2016, PMID 27456526), and stiffness predicts incident diabetes as well as incident hypertension (Cohen 2022, PMID 35946401). Microvascular remodelling and rarefaction, endothelial dysfunction and smooth-muscle phenotype switching complete the vascular picture (Totoń-Żurańska 2024, PMID 38920058; de Oliveira 2022, PMID 36174768; Durante 2024, PMID 39769057).

Immunity and inflammation

Adaptive immune activation is required for full expression of experimental hypertension: T-cell subsets, monocyte/macrophage infiltration of kidney and perivascular fat, and regulatory T-cell deficiency all modulate the pressure response to angiotensin II and to salt (Caillon 2019, PMID 29952002; Gan 2024, PMID 38044398; Zhang 2022, PMID 36703963; Varadarajan 2025, PMID 41121514). Human genetic support comes from SH2B3/LNK, a GWAS blood-pressure locus with an immune mechanism: the risk polymorphism promotes hypertension development and renal damage in a mouse knock-in model (Alexander 2022, PMID 36169218). Regulatory T cells are protective across cardiovascular disease models (Meng 2016, PMID 26525543; Hu 2023, PMID 37840195). No immunomodulatory therapy for hypertension has reached late-phase trials, which is the field's honest position.

Salt sensitivity and tissue sodium

Salt sensitivity — a reproducible pressure fall on sodium restriction — is a phenotype, not a mechanism, and is defined differently in nearly every study, which is why prevalence estimates diverge (Weinberger 1993, PMID 7922236; Iatrino 2016, PMID 27614755; Mishra 2018, PMID 30170653). Mechanisms proposed include impaired renal dopaminergic natriuresis (Zhang 2015, PMID 25594544), endothelial and vascular dysfunction with sex-specific features (Butler 2025, PMID 40144661; Luzardo 2015, PMID 26028243), and distal-nephron transport regulation (Nishimoto 2024, PMID 38545804).

The sharpest challenge to the classical two-compartment account of sodium is tissue storage. ²³Na magnetic resonance imaging shows sodium accumulating in skin and muscle in amounts not accounted for by measured water, rising with age and higher in people with hypertension and in refractory hypertension (Kopp 2013, PMID 23339169); sodium can be mobilised from these stores by dialysis (Dahlmann 2015, PMID 25100048), and renal denervation has been associated with changes in tissue sodium content in treatment-resistant hypertension (Ott 2018, PMID 28845508). If sodium balance is not "just a renal affair" (Titze 2014, PMID 24401786; Titze 2015, PMID 25470013; Hofmeister 2015, PMID 25600900), then both the interpretation of 24-hour urinary sodium as an intake proxy and the classical pressure-natriuresis argument need modification.

Obesity

Obesity is the largest single population driver of rising blood pressure. Mechanisms are multiple and reinforce each other: leptin-driven sympathetic activation, renin-angiotensin activation from adipose tissue, physical compression of the kidney by perirenal and sinus fat, hyperinsulinaemia and increased distal tubular sodium reabsorption (Hall 2015, PMID 25767285; Kotsis 2010, PMID 20442753; Parvanova 2024, PMID 38186879). Molecular routes to sodium retention in obesity include AMPK-dependent SPAK/OSR1 regulation of NKCC2 (Davies 2014, PMID 24808538). Insulin resistance also independently drives arterial stiffening (Hill 2021, PMID 33766485).

Gut microbiome

Germ-free and antibiotic-transfer experiments implicate the microbiota in blood-pressure regulation; the leading mechanistic candidate is short-chain fatty acid signalling through host receptors. Propionate protected against hypertensive cardiac and vascular damage in mice (Bartolomaeus 2019, PMID 30586752), and GPR41/43 sensing of microbial metabolites was protective in a subsequent model (Muralitharan 2025, PMID 39840468). Reviews are appropriately cautious about the translational distance (O'Donnell 2023, PMID 36631562; Verhaar 2020, PMID 33003455; Wu 2021, PMID 34650536).

How the mechanisms map onto drugs

Mechanism Drug class acting on it
Distal sodium reabsorption Thiazide-type diuretics; amiloride; mineralocorticoid receptor antagonists
Angiotensin II generation/action ACE inhibitors, ARBs; angiotensinogen siRNA (Desai 2023, PMID 37467498)
Aldosterone synthesis Aldosterone synthase inhibitors (Freeman 2023, PMID 36342143)
Vascular tone Calcium channel blockers; endothelin antagonism (Schlaich 2022, PMID 36356632)
Sympathetic outflow β-blockers, central α2 agonists; renal denervation (Böhm 2020, PMID 32234534)

Open questions

  • Is the pressure-natriuresis account correct as a necessary condition for chronic hypertension, or is it a modelling artefact? (Guyton 1980, PMID 6994602; Kurtz 2016, PMID 28637271; Evans 2016, PMID 26582636)
  • If tissue sodium storage is quantitatively significant, what does 24-hour urinary sodium actually measure in cross-sectional studies, and does that change the interpretation of the sodium–outcome literature? (Titze 2014, PMID 24401786; Kopp 2013, PMID 23339169)
  • Can salt sensitivity be given an operational definition stable enough to be a treatment-selection variable rather than a research phenotype? (Iatrino 2016, PMID 27614755)
  • Is immune activation causal in human hypertension, and would an immunomodulatory intervention lower pressure without unacceptable harm? No such trial exists (Caillon 2019, PMID 29952002; Alexander 2022, PMID 36169218).
  • Does the microbiome–SCFA axis produce blood-pressure effects in humans of a size worth targeting? (Bartolomaeus 2019, PMID 30586752; O'Donnell 2023, PMID 36631562)

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