Vasoactive intestinal peptide is a 28 amino acid neuropeptide, and both halves of that name undersell it. It was named for a sharp drop in systemic blood pressure observed after isolation from porcine small intestine in the early 1970s, and it turned out to act as a general modulator across nearly every organ system. The evidence base is unusually solid for a peptide, built on human physiology and decades of receptor pharmacology rather than the thin preclinical record surrounding most compounds sold in the peptide market, and the limiting fact is not what the molecule does but how briefly it survives.
Vasoactive intestinal peptide is a 28 amino acid neuropeptide signaling through the VPAC1 and VPAC2 receptors across the gut, vasculature, airways, brain and immune system, with a plasma half life of only one to two minutes that confines it to local paracrine and neurocrine action.
The 28 residue chain does two different jobs at its two ends, and that split explains most of what the molecule can and cannot be made to do. The N terminal residues drive receptor activation while the C terminal helix supplies binding affinity, so trimming a few residues off the front converts an agonist into a weak antagonist, which is the basis for several research probes. The same composition that makes the peptide work also makes it awkward to handle in a laboratory.
The mature peptide is a single 28 amino acid chain whose N terminal residues form the receptor activation domain and whose C terminal helix from roughly residue 15 onward supplies binding affinity, so removal of even a few N terminal residues converts the agonist into a weak antagonist.
Production is neuronal rather than glandular, and that single fact governs how the peptide behaves everywhere else. Nerve terminals package it in large dense-core vesicles and release it in bursts into the tissue immediately around them, so low level activity releases mostly conventional transmitters while intense stimulation recruits the peptide as well. Resting plasma levels in healthy adults sit in the low tens of picograms per milliliter, averaging about 42 picograms per milliliter in one control series, and hold in that range even during vigorous gut activity.
Vasoactive intestinal peptide is produced overwhelmingly by neurons rather than glands, with the enteric nervous system as the single largest source, and resting plasma concentrations of only a few tens of picograms per milliliter in healthy adults mean any sustained elevation in blood points to abnormal secretion rather than normal physiology.
One peptide producing such different effects in different tissues is a receptor distribution story, not a molecule story. VPAC1 and VPAC2 bind it with roughly equal low nanomolar affinity but sit in different organs, which is why subtype selectivity is the main lever available to a drug developer and why clean discrimination has proved hard, since the two share a highly similar peptide binding groove.
| Feature | VPAC1 | VPAC2 | PAC1 |
|---|---|---|---|
| Affinity for VIP | Low nanomolar | Low nanomolar | Several hundred to 1000-fold lower |
| Dominant tissues | Lung, gut epithelium, liver, thymus, T cells | Vascular and airway muscle, islets, stomach, suprachiasmatic nucleus | Central nervous system, adrenal medulla |
| G protein coupling | Gs, cyclic AMP | Gs, cyclic AMP, secondary Gq in some tissues | Gs and Gq |
| Preferred ligand | VIP and PACAP roughly equally | VIP and PACAP roughly equally | PACAP |
Vasoactive intestinal peptide acts through the class B receptors VPAC1 and VPAC2, which bind it with roughly equal low nanomolar affinity and couple to Gs to raise cyclic AMP, while the third family member PAC1 binds it several hundred to a thousand fold more weakly and functions as a PACAP receptor at physiological concentrations.
Relaxation is the common thread, and the mechanism barely changes from the colon to the pulmonary artery. What differs between tissues is the consequence: receptive relaxation ahead of a bolus in the bowel, a fall in systemic vascular resistance with a compensatory rise in heart rate and cardiac output when the peptide is infused intravenously.
In the gastrointestinal tract vasoactive intestinal peptide is the dominant non-adrenergic non-cholinergic inhibitory transmitter, and the epithelial chloride secretion it drives becomes clinically dramatic under continuous tumor stimulation, generating stool volumes that can exceed three liters per day.
The immune system does not just respond to this peptide, it manufactures it: activated T cells transcribe the gene and release it into the local microenvironment, creating an autocrine and paracrine loop with no nerve involvement at all. The dominant effect across both innate and adaptive arms is restraint. That breadth is also the hazard, since sustained pharmacological activation of a mediator this broadly suppressive would be expected to impair host defense against intracellular pathogens.
Vasoactive intestinal peptide is produced by activated T cells and suppresses inflammation through VPAC1 and VPAC2 on macrophages, dendritic cells and lymphocytes, but the disease-modifying evidence for that pathway comes from animal models rather than human clinical trials.
Roughly ten percent of the neurons in the suprachiasmatic nucleus produce this peptide, and they occupy the ventrolateral core region that receives direct retinal input. Every clock neuron carries its own molecular oscillator built from the Period, Cryptochrome, CLOCK and BMAL1 feedback loop, but those oscillators run at slightly different intrinsic periods and would drift apart within days without a coupling signal. The loss-of-function evidence identifying this peptide as that signal is unusually clean for a neuropeptide.
Roughly ten percent of suprachiasmatic nucleus neurons produce vasoactive intestinal peptide, and its rhythmic release onto VPAC2 receptors is the coupling signal that holds individual clock cells in phase, with animals lacking the peptide or the receptor losing circadian firing rhythms in about half of all suprachiasmatic neurons.
Excess is the far better characterized direction and it is a diagnosable disease rather than a theoretical concern. A secreting tumor produces diarrhea that is secretory rather than osmotic, so it persists through fasting, which is the feature that separates it from most other causes. The assay itself is a trap for the unwary: the peptide degrades within minutes at room temperature, so a sample that is not drawn into a chilled tube with a protease inhibitor, spun cold and frozen promptly can read falsely low and mask a real tumor.
| Feature | Excess (VIPoma) | Deficiency states |
|---|---|---|
| Driver | Pancreatic islet neuroendocrine tumor, about 1 case per 10 million per year | Loss of peptidergic inhibitory neurons or reduced expression |
| Plasma level | Commonly 250 to 500 pg/mL against a reference below about 190 pg/mL | No established diagnostic threshold |
| Presentation | Watery diarrhea above 3 L/day, hypokalemia, achlorhydria, flushing, hypercalcemia | Achalasia, Hirschsprung disease, idiopathic pulmonary arterial hypertension |
| Documented management | Fluid and electrolyte correction, then octreotide or lanreotide; resection can be curative | No approved replacement therapy |
A VIPoma occurs in roughly one person per ten million per year and presents with fasting-persistent secretory diarrhea that commonly exceeds three liters per day alongside a fasting plasma level typically reported at 250 to 500 picograms per milliliter, against a laboratory reference range below roughly 190 picograms per milliliter.
About one minute. Infusion studies place the circulating half life at roughly one to two minutes, among the shortest of any signaling peptide in human physiology, with several enzyme systems sharing the work: neprilysin cleaving internal bonds on endothelial and epithelial surfaces, dipeptidyl peptidase 4 trimming the N terminal activation domain, mast cell tryptase and chymase acting at sites of inflammation, and plasma aminopeptidases and the liver clearing the remainder. That fragility is the point rather than a flaw, since a signal that relaxes muscle, dilates vessels, drives secretion and suppresses immune activation would be dangerous if it lingered.
The circulating half life of vasoactive intestinal peptide is roughly one to two minutes with a metabolic clearance rate near nine milliliters per kilogram per minute, which is why intravenous infusion of the native peptide produces flushing, tachycardia and hypotension before a useful tissue concentration can be sustained anywhere.
The lung is where this peptide comes closest to being a workable drug, for a reason that has nothing to do with the lung itself: an inhaled dose reaches airway and pulmonary vascular receptors directly without first surviving the bloodstream. Peptide-containing fibers run with cholinergic nerves from trachea to bronchioles and along the pulmonary arteries, forming the main inhibitory non-adrenergic non-cholinergic input to the airway. Human evidence remains limited to small studies of inhaled peptide reporting improvements in pulmonary hemodynamics.
Vasoactive intestinal peptide is one of the most potent endogenous bronchodilators identified and lowers pulmonary arterial pressure and resistance through VPAC2, but the human record consists of small inhaled studies of pulmonary hemodynamics rather than an approved respiratory therapy.
Educational use only. This article describes what the published scientific and clinical literature reports about Vasoactive Intestinal Peptide. It is not medical advice, and it does not recommend, prescribe, or tell anyone to use anything described here. The regulatory status shown at the top of this page reflects what the record showed on the date given there and can change. mdpep.com does not sell any substance described here, does not endorse human use of it, and does not direct anyone to obtain it.
Talk to a licensed prescriber. Whether a treatment described here is appropriate for you depends on your medical history, your current medications, and the monitoring you may need. A licensed healthcare provider can evaluate your situation.
This is not guidance for your situation. Nothing here accounts for your medical history, your current medications, or anything else specific to you, and none of it should be used to make a decision about your own health.
Affiliate disclosure. Some links on this site are affiliate links, and mdpep.com may earn a commission when they are used. That never affects what is written here, it is not an endorsement of any vendor, and it is not a statement that anything described on this page is available to buy.
Every claim here ties to a named primary source and a date, written as plain documentation with nothing for sale. That is how MD PEP covers the whole peptide market.
