First Evidence That Neuropeptide Y Blood Vessel Constriction Is Overridden by Exercise in Humans | Research

The takeaway

For the first time in humans, researchers showed that exercise metabolically inhibits neuropeptide Y-mediated vasoconstriction to a similar degree as noradrenaline-mediated constriction, ensuring adequate blood flow to working muscles.

52% override
Exercise reduced NPY-mediated vasoconstriction by 52%, not significantly different from the 68% override of α1-adrenergic constriction — the first proof that functional sympatholysis works for this neuropeptide in humans

What the researchers found

In 12 healthy adults during forearm handgrip exercise (15% maximum):

• Phenylephrine (α1-adrenergic) vasoconstriction was attenuated during exercise vs control: ΔFVC -17±9% vs -44±25% (P=0.002), representing 68±18% sympatholysis

• NPY (Y1 receptor) vasoconstriction was similarly attenuated: ΔFVC -11±7% vs -32±22% (P=0.029), representing 52±34% sympatholysis

• No significant difference in sympatholysis magnitude between PE and NPY (68% vs 52%, P=0.28)

This is the first demonstration that NPY-mediated vasoconstriction is sensitive to metabolic inhibition during exercise in humans, confirming that functional sympatholysis extends beyond the classical adrenergic pathway to include the neuropeptide Y system.

Why it matters

Understanding how the body balances blood vessel constriction and muscle blood flow during exercise is fundamental to exercise physiology and cardiovascular medicine. NPY is released in large amounts during intense exercise and stress, and its vasoconstriction is more sustained than noradrenaline's. Knowing that the body can override NPY signaling during exercise reassures us that this potent neuropeptide doesn't impair muscle blood flow — and opens questions about conditions where this override might fail.

How the study worked

12 healthy adults (7 male, mean age 30, BMI 24.9) underwent brachial artery catheterization for direct intra-arterial drug infusion and blood pressure measurement. Forearm blood flow was measured by Doppler ultrasound. Vasoconstrictor responses to phenylephrine (α1-agonist) and NPY (Y1 receptor agonist) were compared during two conditions: (1) sodium nitroprusside infusion (non-metabolic vasodilatory control) and (2) dynamic rhythmic handgrip exercise at 15% maximal voluntary contraction. Changes in forearm vascular conductance quantified sympatholysis.

What this study cannot tell us

Small sample size (12 subjects). Only moderate-intensity handgrip exercise was tested (15% MVC); results may differ at higher intensities or with larger muscle groups. The study was conducted in young, healthy adults — functional sympatholysis may be impaired in clinical populations. Intra-arterial drug infusion creates a pharmacological model that may not perfectly replicate endogenous NPY release. The study measured acute effects only.

How to read the evidence

This is a well-designed human experimental physiology study using invasive methods (arterial catheterization, intra-arterial drug infusion) in healthy volunteers. The paired design (each subject serves as their own control) strengthens the findings despite the small sample size. This represents high-quality mechanistic evidence in healthy humans.

When this study was published

Published in 2025, this study provides novel mechanistic data on a previously unstudied aspect of exercise physiology. As the first demonstration of NPY sympatholysis in humans, it establishes a new line of investigation.

The bigger picture

Neuropeptide Y is one of the most abundant neuropeptides in the human body and plays roles far beyond blood vessel control — including appetite regulation, stress responses, and immune function. This study adds exercise physiology to NPY's functional profile, showing that despite being one of the most potent vasoconstrictors known, its effects are actively overridden by exercising muscles. This has implications for conditions where sympatholysis may be impaired, such as heart failure, hypertension, and aging.

Questions still open

Is NPY sympatholysis impaired in conditions like heart failure or hypertension, where exercise blood flow is already compromised?
Does aging reduce the body's ability to override NPY-mediated vasoconstriction during exercise?
At higher exercise intensities where NPY release increases substantially, does sympatholysis remain adequate?

Common questions

What is functional sympatholysis?

During exercise, your body faces a conflict: the sympathetic nervous system wants to constrict blood vessels (raising blood pressure), but your working muscles need more blood flow, not less. Functional sympatholysis is the body's solution — exercising muscles locally override the constriction signals, allowing blood to flow freely to where it's needed. This study showed for the first time that this override works for neuropeptide Y, not just the better-known noradrenaline system.

Why does neuropeptide Y matter during exercise?

NPY is co-released with noradrenaline from sympathetic nerves during exercise and stress. It's one of the most potent blood vessel constrictors in the body, and its effects last longer than noradrenaline's. Until this study, nobody knew whether the body could override NPY's constriction during exercise. The finding that it can (reducing NPY's effect by about 52%) means that even this powerful neuropeptide doesn't impair muscle blood flow during physical activity.

Read the original research

Functional sympatholysis of neuropeptide Y-mediated vasoconstriction in humans.

The Journal of physiology, 603(11), 3329-3340

View on PubMed ↗Publisher’s paper ↗

Citation

Wakeham, Denis J; Hissen, Sarah L; MacNamara, James P; Davis, Scott L; Fadel, Paul J; Levine, Benjamin D; Hearon, Christopher M. (2025). Functional sympatholysis of neuropeptide Y-mediated vasoconstriction in humans.. The Journal of physiology, 603(11), 3329-3340. https://doi.org/10.1113/JP288412