A neural clue for GLP-1 drugs’ heart rate bump
In an in vitro rat brainstem-spinal cord setup, exendin-4 increased sympathetic nerve activity and depolarized key neurons, supporting a direct neural route for GLP-1 receptor agonist tachycardia.
One of the oddities of glucagon-like peptide 1 (GLP-1) receptor agonists is that their cardiovascular story is, in a sense, two stories.
On the big scoreboard, multiple agents in the class reduce major adverse cardiovascular events in people with type 2 diabetes and related cardiometabolic risk. But at the level of day-to-day physiology, many GLP-1 receptor agonists also raise heart rate a little, and the mechanism has never felt fully settled.
A new paper in Hypertension Research takes a deliberately reductionist swing at that question: can a GLP-1 receptor agonist directly excite the neural machinery that drives sympathetic outflow? In a newborn rat brainstem-spinal cord preparation, the answer was yes, at least for exendin-4 (PubMed).
The clinical “heart rate bump” is real, but it is not uniform
A useful reminder from the older literature is that heart rate effects vary across the class.
A 2017 review that compiled 24 hour monitoring data described a pattern clinicians often recognize informally: short acting GLP-1 receptor agonists tend to produce smaller, more transient changes, while some long acting agents can produce larger and more sustained increases in mean 24 hour heart rate (PubMed).
That heterogeneity is one reason mechanism debates have persisted. If the effect were identical across molecules, it would be easier to pin on a single receptor location or a single reflex.
What this new study tested, step by step
Koyanagi and colleagues focused on exendin-4 (a widely used GLP-1 receptor agonist tool compound) and asked whether it can increase sympathetic activity through direct effects on sympathetic related neurons.
They used in vitro preparations from newborn rats (postnatal day 0 to 4), and looked at three levels:
- Sympathetic nerve trunk activity (a direct readout of sympathetic output).
- Preganglionic neurons in the intermediolateral cell column in the upper thoracic spinal cord, which are key relay neurons for sympathetic control.
- Neurons in the rostral ventrolateral medulla, a classic brainstem hub for sympathetic tone and blood pressure regulation.
When they applied exendin-4 (20 to 100 nM), they saw increases in sympathetic nerve activity, and they saw membrane depolarization in both spinal and medullary neurons at 100 nM.
They also reported a pharmacology sanity check: the sympathetic nerve activity increase was blocked by a GLP-1 antagonist.
Why the “direct excitation” angle matters
The simplest story for a higher heart rate is a generic compensatory reflex: change blood pressure, trigger a baroreflex, end up with a higher pulse.
But the GLP-1 receptor agonist heart rate signal has been stubbornly hard to reduce to a single peripheral explanation. That is why central and autonomic mechanisms keep returning.
This new paper’s value is that it tests one specific claim under controlled conditions: a GLP-1 receptor agonist can directly increase sympathetic output by exciting sympathetic related neurons in the spinal cord and brainstem.
If that claim holds up across models, it helps reconcile several observations that otherwise feel disconnected: a class effect that tracks with duration of action, sympathetic fingerprints in some settings, and persistent tachycardia signals even when you manipulate particular upstream GLP-1 producing circuits.
For example, in a 2020 Molecular Metabolism study, systemic exendin-4 increased heart rate in mice and the effect was abolished by beta adrenergic blockade, consistent with sympathetic involvement. But the authors also found that the drug induced tachycardia did not require recruitment of nucleus tractus solitarius preproglucagon neurons, a major brain source of GLP-1 (PubMed). That kind of result pushes you to look for alternative neural entry points downstream.
Koyanagi et al. are, in effect, pointing at a plausible downstream route.
What this does not resolve
Even if you buy the mechanistic direction, there are clear limits.
The preparation uses newborn rat tissue at a lower temperature than adult physiology, and it is intentionally stripped of many real world feedback loops. It tells you “this can happen” more than it tells you “this is the dominant reason heart rate rises in humans taking semaglutide.”
It also does not settle the question of where in the body the key receptor population is for drug induced tachycardia. The 2017 review explicitly raised two broad possibilities: a direct sinoatrial node effect and or sympathetic stimulation, potentially varying by molecule and pharmacokinetics (PubMed). The new in vitro work strengthens the sympathetic half of that hypothesis, but it does not exclude the other half.
Why this is worth watching anyway
As GLP-1 receptor agonists move into longer duration use and wider populations, small physiological shifts become more than trivia. Not because every heart rate increase is dangerous, but because it is one of the few consistent “non metabolic” signals the class produces.
The most decision relevant next data would look like this:
- adult in vivo experiments that map which spinal and medullary neurons are necessary for the response,
- comparisons across multiple GLP-1 receptor agonists (short acting vs long acting),
- and quantitative links between changes in sympathetic activity and changes in heart rate across settings.
If those pieces line up, clinicians may eventually be able to treat the heart rate bump less like an unexplained footnote and more like a predictable, mechanistically grounded feature of the class.
Further reading
- Koyanagi Y, et al. The effects of glucagon-like peptide-1 receptor agonists on sympathetic neuron activity (2026). PubMed (DOI: 10.1038/s41440-026-02633-5)
- Lorenz M, et al. Differential effects of glucagon-like peptide-1 receptor agonists on heart rate (2017). PubMed
- Holt MK, et al. PPG neurons in the nucleus of the solitary tract modulate heart rate but do not mediate GLP-1 receptor agonist-induced tachycardia in mice (2020). PubMed