Alpha-methyl-para-tyrosine, universally abbreviated as AMPT and known pharmacologically as metyrosine, represents one of the most vital pharmacological tools in behavioral neuroscience and neurochemistry. By selectively inhibiting the rate-limiting enzyme in catecholamine biosynthesis, AMPT allows investigators to transiently deplete central and peripheral dopamine and norepinephrine pools, thereby establishing causal relationships between neurochemical signaling and neuropsychiatric phenomena. This comprehensive academic dictionary entry provides a rigorous examination of AMPT, spanning its biochemical foundations, historical significance, clinical applications, experimental paradigms, and neurobiological implications.
Alpha-Methyl-para-Tyrosine (AMPT)
1. Concise Definition
Alpha-methyl-para-tyrosine (AMPT), or metyrosine, is a synthetic methylated analog of the amino acid L-tyrosine that functions as a competitive and selective inhibitor of tyrosine hydroxylase, the primary rate-limiting enzyme responsible for the conversion of tyrosine to L-DOPA. By obstructing this initial enzymatic step, AMPT potently halts the de novo biosynthesis of the endogenous catecholamines dopamine, norepinephrine, and epinephrine across both central and peripheral nervous systems.
In experimental neuropsychopharmacology and clinical psychiatric research, AMPT is utilized extensively as a reversible chemical tool to produce acute catecholamine depletion in vivo. Administered under controlled protocols, it enables scientists to interrogate monoaminergic hypotheses regarding affective disorders, reward mechanisms, motor functioning, and addiction. In clinical therapeutics, it functions as an antihypertensive and pre-operative adjunct for patients diagnosed with catecholamine-secreting neuroendocrine tumors, notably pheochromocytoma.
2. Etymology & Linguistic Origin
The systematic chemical name of AMPT is derived directly from classical chemical nomenclature. The prefix alpha- (α) originates from the Greek letter designating the first carbon atom adjacent to the carboxylic acid functional group in organic chemistry. The term methyl traces back through French to the Greek roots methy (meaning wine or spirit) and hyle (meaning wood or material), signifying a single-carbon univalent hydrocarbon radical (-CH3). The positional descriptor para- is rooted in the Greek preposition para, signifying “beside” or “beyond,” denoting opposite substitution positions (1,4-disubstitution) on a classical benzene ring.
The root term tyrosine was coined in the nineteenth century by German chemist Justus von Liebig, who first isolated the amino acid from cheese, deriving the name from the classical Greek noun tyros (τυρóς), meaning “cheese.” Pharmacologically, the non-proprietary international designation metyrosine represents a portmanteau condensing methyl and tyrosine. The compound entered the biomedical literature during the mid-1960s as a structural analog synthesized specifically to disrupt monoaminergic pathways.
3. Pronunciation & Grammatical Form
The abbreviation AMPT is pronounced phonetically as an initialism: /ˌeɪ.ɛm.piːˈtiː/ (ay-em-pee-tee). Its systematic pharmaceutical name, metyrosine, is pronounced /mɛt.aɪˈroʊ.siːn/ (met-eye-ROH-seen), or alternatively /məˈtaɪ.rə.siːn/.
Grammatically, AMPT functions as a proper noun when referring to the specific chemical compound or acronym, and as a common noun when categorized within drug classifications (e.g., “an AMPT challenge”). It frequently operates as an attributive noun or adjectival modifier in neurobiological literature, as observed in phrases such as “AMPT-induced catecholamine depletion,” “AMPT administration protocol,” and “AMPT paradigm.” The standard international non-proprietary name (INN) and United States Adopted Name (USAN) is metyrosine, while alpha-methyl-p-tyrosine remains the primary designation across biochemical and neurochemical disciplines.
4. Detailed Conceptual Explanation
To conceptualize the biological actions of AMPT, one must examine the biosynthetic cascade of the catecholamine neurotransmitters. Within central monoaminergic neurons, chromaffin cells of the adrenal medulla, and postganglionic sympathetic fibers, catecholamine generation begins with the active transport of the dietary amino acid L-tyrosine across cell membranes and the blood-brain barrier. Intracellularly, L-tyrosine is hydroxylated to 3,4-dihydroxy-L-phenylalanine (L-DOPA) through the catalytic activity of tyrosine hydroxylase (TH), a tetrameric, iron-containing, pterin-dependent monooxygenase.
Tyrosine hydroxylase exhibits strict substrate specificity and represents the slowest, rate-limiting stage in the overall synthesis cascade. Once L-DOPA is synthesized, it is rapidly converted to dopamine by aromatic L-amino acid decarboxylase (AADC). In noradrenergic and adrenergic cells, dopamine is subsequently converted to norepinephrine by dopamine beta-hydroxylase (DBH), and ultimately to epinephrine by phenylethanolamine N-methyltransferase (PNMT). Because downstream enzymes operate with high catalytic velocities and possess broad capacities, pharmacological disruption of tyrosine hydroxylase produces an insurmountable bottleneck that starves downstream biosynthetic operations.
AMPT functions as a competitive inhibitor of tyrosine hydroxylase with respect to the substrate L-tyrosine. Possessing an additional methyl group at the alpha-carbon, AMPT fits into the active catalytic pocket of the enzyme, directly competing with endogenous L-tyrosine for binding coordinates. Because it cannot undergo normal hydroxylation into an active downstream intermediate, it stabilizes an inactive enzyme-inhibitor conformation. As cellular stores of vesicular dopamine and norepinephrine undergo routine physiological exocytosis, metabolic breakdown via monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT), and reuptake, the intracellular pools cannot be replenished de novo.
Consequently, systemic or central administration of AMPT initiates a rapid, progressive decay in overall catecholamine concentrations. In experimental animals and human subjects, oral or parenteral delivery leads to measurable decrements in tissue catecholamine levels within hours, reaching peak depletion typically between 24 and 48 hours following repeated administration. The pharmacological effects are reversible; cessation of AMPT exposure allows the uninhibited de novo synthesis of catecholamines to resume, restoring baseline neurochemical equilibrium within 48 to 72 hours.
5. Historical Development
The discovery and characterization of AMPT emerged during the golden age of neuropharmacology in the early 1960s, a period marked by intensive efforts to isolate the metabolic machinery governing the autonomic nervous system and neuropsychiatric states. In 1965, Sidney Spector, Albert Sjoerdsma, and Sidney Udenfriend published seminal investigations demonstrating that alpha-methyl-para-tyrosine specifically and potently inhibited tyrosine hydroxylase in vitro and provoked profound reductions in tissue norepinephrine levels in guinea pigs and rats.
Prior to the synthesis of AMPT, investigators relied heavily on reserpine to deplete monoamines. However, reserpine irreversibly blocks the vesicular monoamine transporter (VMAT-1 and VMAT-2), indiscriminately depleting not only dopamine and norepinephrine but also serotonin (5-HT) and histamine throughout the central and peripheral systems. The arrival of AMPT provided researchers with an unprecedented selective instrument that left serotonergic and histaminergic pathways fundamentally undisturbed, establishing a new gold standard for catecholamine-specific research.
Throughout the late 1960s and 1970s, clinicians applied AMPT therapeutically to combat the dangerous cardiovascular storms associated with pheochromocytoma, a rare catecholamine-producing tumor of the adrenal chromaffin tissue. Albert Sjoerdsma led human clinical trials that culminated in the drug’s regulatory approval by the United States Food and Drug Administration (FDA) under the trade name Demser in 1979.
During the late 1980s and 1990s, neuroimaging breakthroughs, such as Positron Emission Tomography (PET) and Single-Photon Emission Computed Tomography (SPECT), transformed AMPT into a cognitive and diagnostic probe. Researchers such as Dennis Charney, Richard Neiman, Wayne Drevets, and Anissa Abi-Dargham began utilizing the “AMPT challenge” in humans. By pairing acute catecholamine depletion with radiotracers, investigators could measure endogenous dopamine release, receptor occupancy, and vulnerability to depressive relapse in clinical populations, cementing AMPT as an indispensable instrument in biological psychiatry.
6. Theoretical Foundations
The empirical deployment of AMPT is historically and theoretically tethered to the Monoamine Hypothesis of Affective Disorders. Formulated independently by Joseph Schildkraut and Alec Coppen in the mid-1960s, this hypothesis proposed that depressive states arise from a fundamental functional deficit of central monoamines—specifically norepinephrine and serotonin—at central synaptic junctions, while mania reflects an absolute or relative excess. AMPT served as an acid test for this hypothesis: if reducing norepinephrine or dopamine precipitates clinical depression in healthy individuals, the causal link gains robust support.
Remarkably, experimental results obtained via AMPT modified these early deterministic views. When administered to healthy, drug-naive volunteers without psychiatric illness, marked catecholamine depletion typically evokes mild sedation, cognitive slowing, and fatigue, but consistently fails to trigger the complete syndrome of major depressive disorder. However, when administered to remitted depressed patients who successfully recovered via treatment with noradrenergic antidepressants (such as desipramine or reboxetine), AMPT provokes a rapid, transient relapse of depressive symptoms. Conversely, remitted patients maintained on selective serotonin reuptake inhibitors (SSRIs) generally remain resistant to AMPT-induced relapse, demonstrating distinct, neurochemically segregated maintenance pathways in affective recovery.
Furthermore, AMPT plays a crucial role in modern theories of dopamine receptor availability and reward prediction error. Within contemporary computational neuroscience and neuroimaging frameworks, basal tone dopamine competes directly with radiotracers (such as [11C]raclopride or [18F]fallypride) for binding to dopamine D2 and D3 receptors. By utilizing AMPT to clear endogenous dopamine from synaptic clefts, neuroscientists can measure the absolute baseline receptor availability in vivo, providing empirical foundations for theoretical models of tonic versus phasic dopamine release.
7. Key Components, Types & Dimensions
The study and application of AMPT can be categorized across distinct chemical, biological, and clinical dimensions:
- Stereochemical Enantiomers: AMPT exists as two stereoisomers: the L-enantiomer (active) and the D-enantiomer (biologically inactive). Pharmacological preparations utilize either the racemate (DL-AMPT) or pure L-metyrosine, with the L-isomer possessing exclusive inhibitory activity against tyrosine hydroxylase.
- Molecular Mechanism of Action: AMPT operates strictly as a competitive, reversible inhibitor at the catalytic site of tyrosine hydroxylase. Unlike irreversible toxins (such as 6-hydroxydopamine), AMPT preserves neuronal architecture, terminating its inhibitory actions as cellular concentrations fall.
- Substrate Selectivity: AMPT exhibits high specificity for tyrosine hydroxylase, leaving aromatic L-amino acid decarboxylase, tryptophan hydroxylase, and dopamine beta-hydroxylase directly unaffected, thereby leaving serotonin and indolamine synthesis structurally unimpaired.
- Target Systems: AMPT targets both peripheral sympathetic neurons and neuroendocrine chromaffin tissue, alongside central catecholaminergic circuits, including the nigrostriatal, mesolimbic, mesocortical, and tuberoinfundibular dopamine pathways, as well as locus coeruleus noradrenergic projections.
- Dosing Paradigms: Research paradigms differentiate between sub-chronic depletion (oral regimens delivering 3 to 4.5 grams over a 24-to-48-hour cycle to achieve 60–80% catecholamine reduction) and acute rodent paradigms (single intraperitoneal injections ranging between 100 and 300 mg/kg).
8. Examples & Illustrative Cases
To understand the translational value of AMPT, examine the following clinical and experimental paradigms:
Case 1: Pre-Surgical Optimization in Pheochromocytoma
A 48-year-old patient presents with paroxysmal episodes of severe cephalea, diaphoresis, palpitation, and malignant hypertension exceeding 220/130 mmHg. Biochemical screening reveals twenty-fold elevations in plasma free normetanephrine and metanephrine, while abdominal magnetic resonance imaging confirms a 5.5 cm mass in the left adrenal gland consistent with pheochromocytoma. Although classical management utilizes alpha-adrenergic antagonists like phenoxybenzamine, the surgical team encounters labile hemodynamic instability. Oral metyrosine is initiated at 250 mg four times daily and titrated to 2 grams per day over five days prior to laparotomy. AMPT downregulates the de novo synthesis of catecholamines inside the tumor tissue, stabilizing intraoperative arterial blood pressure during surgical manipulation of the adrenal gland and preventing hypertensive crisis.
Case 2: The Depletion Paradigm in Affective Neuroscience
A 35-year-old participant with recurrent major depressive disorder has been symptom-free for twelve months while maintained on the selective noradrenaline reuptake inhibitor atomoxetine. The participant enters an academic clinical study evaluating catecholaminergic vulnerabilities. On Day 1, baseline clinical scales (such as the Hamilton Depression Rating Scale) are recorded. Under a double-blind, randomized, placebo-controlled crossover design, the participant receives oral AMPT totaling 3.5 grams distributed across 24 hours. By the peak depletion window at Hour 28, the participant exhibits a transient return of classical depressive symptoms, including anhedonia, subjective feelings of worthlessness, and psychomotor deceleration. Forty-eight hours following cessation of AMPT, as endogenous catecholamine synthesis resumes, depressive symptomatology remits entirely, confirming the dependency of the participant’s remission state on noradrenergic tone.
9. Measurement & Assessment
Evaluating the impact and efficacy of AMPT administration requires direct biochemical quantification, physiological monitoring, and neuroimaging parameters:
Biochemically, systemic depletion is monitored via chromatographic analysis of peripheral catecholamines and their major metabolic byproducts. High-Performance Liquid Chromatography (HPLC) coupled with electrochemical detection or liquid chromatography-tandem mass spectrometry (LC-MS/MS) measures levels of plasma dopamine and norepinephrine alongside urinary metabolites: homovanillic acid (HVA, the chief dopamine breakdown product), 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), and vanillylmandelic acid (VMA, the primary noradrenaline and adrenaline breakdown products). Clinical trials verify that successful AMPT regimens reduce urinary and cerebrospinal fluid HVA and MHPG concentrations by approximately 50% to 80% relative to baseline.
In neuroimaging studies, dopamine depletion mediated by AMPT is evaluated through competitive positron emission tomography displacement imaging. Using radioligands that bind reversibly to dopamine D2/D3 receptors (such as [11C]raclopride, [11C]FLB 457, or [18F]fallypride), researchers acquire scans at baseline and post-AMPT. Because AMPT removes endogenous dopamine from the synaptic cleft, fewer receptor sites are occupied by native neurotransmitter molecules. This results in an increased binding potential (BPND) for the injected radioligand. The percentage change in BPND between the baseline and depleted states serves as a direct, non-invasive biomarker of endogenous dopamine levels.
Physiologically and psychometrically, safety and depth of depletion are monitored through orthostatic blood pressure checks, resting pulse rates, continuous urine microscopy (to screen for metyrosine crystalluria), and standardized neuropsychiatric instruments, including the Visual Analogue Scales (VAS) for sedation and the Profile of Mood States (POMS).
10. Applications & Practical Significance
The applications of AMPT extend across both therapeutic medicine and basic cognitive science:
Within therapeutics, metyrosine (Demser) remains a specialized clinical weapon in endocrinology and oncology. Beyond preparing patients for the surgical resection of pheochromocytoma, it provides chronic palliation for malignant, unresectable neuroendocrine paragangliomas where conventional alpha- and beta-blockers cannot prevent catecholamine toxicity. Furthermore, it has been explored experimentally to manage refractory autonomic dysreflexia in spinal cord injuries and severe tardive dyskinesia secondary to antipsychotic use, operating through the chemical dampening of striatal dopamine output.
Within basic and translational neuroscience, AMPT provides an experimental method to disrupt functional circuits. By dissociating catecholaminergic pathways from indolaminergic (serotonergic) circuits, researchers utilize AMPT to map the neurochemical architecture of motivation, incentive salience, attention, and executive working memory in human volunteers. In preclinical psychopharmacology, systemic or intracranial microinfusion of AMPT into rodent models enables researchers to distinguish between neurotransmitter release and de novo synthesis during behavioral tasks assessing operant conditioning, extinction learning, and drug-seeking behavior.
11. Research & Empirical Evidence
Decades of empirical studies have yielded critical insights through the utilization of AMPT:
In schizophrenia research, seminal PET studies led by Anissa Abi-Dargham and colleagues (2000) employed the AMPT challenge to resolve long-standing disputes concerning the nature of dopamine dysregulation. Prior studies had yielded ambiguous results regarding baseline receptor densities in drug-naive patients with schizophrenia. By depleting endogenous dopamine using AMPT prior to [11C]raclopride PET imaging, Abi-Dargham’s group demonstrated that patients with schizophrenia exhibited significantly greater increases in radiotracer binding potential compared to matched healthy controls. This directly proved that schizophrenic pathology involves exaggerated baseline occupancy of striatal D2 receptors by endogenous dopamine, providing direct empirical confirmation of the hyperdopaminergic hypothesis in living human subjects.
In addiction neurobiology, investigations conducted by Martinez et al. (2005, 2007) utilized AMPT challenges to assess striatal dopamine transmission across individuals dependent on cocaine and alcohol. These researchers discovered that, contrary to the hyperdopaminergic states observed in acute psychosis, substance dependence correlates with blunted increases in radioligand binding following AMPT. This confirmed that severe addiction involves a profound downregulation of endogenous dopamine production within ventral and associative striatal subdivisions, driving anhedonia and drug craving.
In affective disorders, foundational investigations by Dennis Charney and colleagues at Yale University demonstrated the neurochemical specificity of antidepressant efficacy. Their clinical trials showed that while AMPT triggered depressive relapses in unipolar patients maintained on norepinephrine reuptake inhibitors, parallel depletion of serotonin using acute tryptophan depletion (ATD) failed to destabilize these individuals. The reverse pattern was observed in patients maintained on serotonergic drugs, empirical proof that the neurochemical pathways underlying clinical remission depend upon the pharmacological mechanism of the original therapeutic intervention.
12. Cultural & Cross-Cultural Considerations
From a cross-cultural perspective, access to and utilization of AMPT vary dramatically based on economic, regulatory, and pharmaceutical infrastructure. Due to complex multi-step synthetic chemistry and a tiny commercial market, metyrosine is an exceptionally expensive orphan drug. In many regions across the Global South and middle-income nations, the clinical utilization of metyrosine for pheochromocytoma is completely unavailable. Clinicians in these areas rely exclusively on non-selective alpha-adrenergic antagonists such as phenoxybenzamine, or selective alpha-1 blockers like doxazosin, combined with aggressive hydration.
Furthermore, human experimental paradigms employing AMPT are heavily concentrated within specialized, highly resourced academic research medical centers across North America and Western Europe due to the stringent safety requirements, ethical board oversight, and expensive neuroimaging equipment (such as dedicated cyclotron-PET suites) required to execute depletion protocols safely. Cross-cultural variations in genetic polymorphisms—such as ethnic variations in the frequency of the Catechol-O-Methyltransferase (COMT) Val158Met allele—also imply that the cognitive and affective impacts of catecholamine depletion by AMPT differ across diverse populations. Individuals homozygous for the Met allele (common in European descent populations), who exhibit slower catecholamine clearance in prefrontal circuits, can respond differently to AMPT depletion compared to populations with higher frequencies of the high-activity Val allele.
13. Criticisms, Debates & Limitations
Despite its vast utility, AMPT faces several substantive scientific criticisms, experimental limitations, and safety concerns:
The principal pharmacological drawback of AMPT is its dual action on both dopamine and norepinephrine. Because tyrosine hydroxylase lies upstream of both neurotransmitters, systemic administration cannot selectively silence dopamine pathways without simultaneously draining noradrenergic networks. Consequently, whenever researchers observe a behavioral or cognitive deficit following AMPT—such as impaired working memory or reduced attention—attributing the outcome definitively to dopamine rather than norepinephrine remains challenging in the absence of complex control studies involving selective receptor rescues.
A critical safety limitation involves metyrosine’s low water solubility at physiological pH. When excreted unchanged by the kidneys into tubular fluids, the compound readily precipitates into microcrystalline lattices, leading to metyrosine crystalluria, hematuria, dysuria, and acute obstructive nephropathy. Human protocols require intensive patient safety measures, including excessive oral hydration (typically exceeding 3 to 4 liters daily) and continuous urine monitoring. Furthermore, severe central dopamine depletion routinely induces acute extrapyramidal symptoms, including muscular rigidity, tremor, akathisia, and psychomotor deceleration, limiting the drug’s acceptability and blinding integrity in placebo-controlled psychological research.
14. Related Terms & Distinctions
To avoid conceptual conflation, AMPT must be distinguished from several related chemical agents and biological mechanisms:
- AMPT vs. Reserpine: While both drugs deplete catecholamines, AMPT is an acute, competitive inhibitor of synthesis acting on tyrosine hydroxylase, leaving serotonin intact. Reserpine irreversibly inhibits the vesicular monoamine transporter (VMAT), preventing vesicular packaging and indiscriminately depleting dopamine, norepinephrine, epinephrine, and serotonin.
- AMPT vs. 6-Hydroxydopamine (6-OHDA): AMPT provokes fully reversible chemical depletion without structural cellular damage. In contrast, 6-OHDA is a neurotoxic compound internalized by catecholamine transporters that causes structural, permanent oxidative death of dopaminergic and noradrenergic neurons.
- AMPT vs. Acute Phenylalanine/Tyrosine Depletion (APTD): AMPT accomplishes depletion pharmacologically via enzyme inhibition. APTD is a dietary manipulation involving the ingestion of an amino acid mixture devoid of phenylalanine and tyrosine, which competitively reduces the entry of dietary catecholamine precursors into the brain through the large neutral amino acid transporter (LAT1).
- AMPT vs. Alpha-Methyldopa: Both are methylated amino acid analogs; however, while AMPT directly inhibits tyrosine hydroxylase, alpha-methyldopa is metabolized via AADC into alpha-methylnorepinephrine, functioning as a central alpha-2 adrenergic receptor agonist.
15. Summary & Key Takeaways
Alpha-methyl-para-tyrosine (AMPT; metyrosine) is the definitive pharmacological inhibitor of tyrosine hydroxylase, the rate-limiting enzyme in catecholamine biosynthesis. By blocking the metabolic conversion of L-tyrosine to L-DOPA, AMPT systematically halts the production of dopamine, norepinephrine, and epinephrine across the central and peripheral nervous systems. Historically instrumental in validating monoaminergic theories of affective disorders and schizophrenia, AMPT remains a gold-standard chemical probe in human neuroimaging and translational neuropsychopharmacology. While clinical use is primarily confined to managing pheochromocytoma, its capacity to safely and reversibly lower synaptic catecholamine tone allows investigators to map receptor availability, evaluate reward mechanics, and examine the biological underpinnings of complex neuropsychiatric diseases.
Ultimately, the continuous integration of the AMPT challenge within advanced neuroimaging paradigms has reshaped contemporary neuroscience, transitioning theoretical models from static neurochemical deficiencies to dynamic assessments of synaptic occupancy and receptor sensitivity. In both clinical medicine and neuropsychopharmacology, AMPT stands as a foundational molecular bridge connecting the biochemistry of amino acid processing to the behavioral physiology of the human brain.
References
- Abi-Dargham, A., Rodenhiser, J., Printz, D., Zea-Ponce, Y., Gil, R., Kegeles, L. S., Weiss, R., Cooper, T. B., Mann, J. J., & Laruelle, M. (2000). Increased baseline occupancy of D2 receptors by dopamine in schizophrenia. Proceedings of the National Academy of Sciences, 97(14), 8104–8109. https://doi.org/10.1073/pnas.97.14.8104
- Charney, D. S., Heninger, G. R., & Sternberg, D. E. (1982). Failure of alpha-methyl-para-tyrosine to alter mood in healthy subjects: Evidence against the catecholamine hypothesis of depression. Psychopharmacology, 76(4), 389–392. https://doi.org/10.1007/BF00432560
- Martinez, D., Gil, R., Slifstein, M., Hwang, D. R., Huang, Y., Perez, A., Kegeles, L., Talbot, P., Evans, S., Krystal, J., & Laruelle, M. (2005). Alcohol dependence is associated with blunted dopamine transmission in the ventral striatum. Biological Psychiatry, 58(10), 779–786. https://doi.org/10.1016/j.biopsych.2005.04.044
- Sjoerdsma, A., Engelman, K., Spector, S., & Udenfriend, S. (1965). Inhibition of catecholamine synthesis in man with alpha-methyl-tyrosine, an inhibitor of tyrosine hydroxylase. The Lancet, 286(7422), 1092–1094. https://doi.org/10.1016/S0140-6736(65)90062-8
- Spector, S., Sjoerdsma, A., & Udenfriend, S. (1965). Blockade of endogenous norepinephrine synthesis by alpha-methyl-tyrosine, an inhibitor of tyrosine hydroxylase. Journal of Pharmacology and Experimental Therapeutics, 147(1), 86–95. https://jpet.aspetjournals.org/content/147/1/86