An 11-amino-acid neuropeptide belonging to the tachykinin family. A key mediator of pain perception, inflammation, and nausea. The NK1 receptor antagonist aprepitant (Emend) — which blocks Substance P — is a major antiemetic drug.
Substance P (SP) is an 11-amino-acid neuropeptide and the founding member of the tachykinin peptide family. It was first discovered in 1931 by Ulf von Euler and John Gaddum as an unidentified substance in brain and gut extracts that caused smooth muscle contraction — they called it 'Preparation P' (P for powder), which became Substance P.
Substance P is released from sensory nerve endings (C-fibers and Aδ fibers) in response to tissue damage, transmitting pain signals to the spinal cord and brain. It also has potent pro-inflammatory effects, stimulating immune cells, promoting vasodilation, and increasing vascular permeability. The discovery that blocking Substance P's receptor (NK1) prevents chemotherapy-induced nausea led to the development of aprepitant (Emend), a blockbuster antiemetic drug.
Substance P is one of the most extensively studied neuropeptides in neuroscience, with a research history spanning over 90 years. It was first identified in 1931 by Ulf von Euler and John Gaddum as an unidentified substance in intestinal tissue extracts that caused smooth muscle contraction — they named it "Substance P" (for "preparation" or "powder"). Its amino acid sequence was determined in 1971, and it was subsequently recognized as the founding member of the tachykinin neuropeptide family.
Substance P's primary clinical relevance is in pain transmission. It is released by sensory nerve endings (C-fibers and Aδ-fibers) in response to tissue injury, inflammation, and noxious stimuli, transmitting pain signals from the periphery to the spinal cord and brain. Blocking Substance P's receptor (NK1R, neurokinin-1 receptor) has been a major target for pain and anti-emetic drug development. Aprepitant (Emend), an NK1R antagonist, is FDA-approved for chemotherapy-induced nausea — validating the therapeutic potential of targeting this pathway.
Beyond pain, Substance P plays roles in inflammation (it is a potent vasodilator and promotes inflammatory cell recruitment), mood regulation (it has been implicated in depression and anxiety), and GI motility. Its widespread distribution throughout the nervous system makes it one of the most functionally diverse neuropeptides known.
Substance P binds to the neurokinin-1 (NK1) receptor, a Gq-coupled GPCR expressed in the spinal cord dorsal horn, brainstem (vomiting center), and peripheral tissues. NK1 activation triggers the PLC-IP3-Ca²⁺ cascade, amplifying pain signals and stimulating inflammatory responses. In the brainstem, NK1 activation in the nucleus tractus solitarius mediates nausea and vomiting — which is why NK1 antagonists like aprepitant are effective antiemetics.
| Pathway | Effect | Significance |
|---|---|---|
| Pain transmission | Released from sensory C-fibers → NK1 on dorsal horn neurons | Mediates slow, burning pain (complements fast glutamate signaling) |
| Neurogenic inflammation | Promotes vasodilation, plasma extravasation, and immune cell recruitment | Causes local redness, swelling, and heat at injury sites |
| Nausea/vomiting | Activates NK1 receptors in brainstem vomiting centers | Mediates chemotherapy-induced nausea (blocked by aprepitant) |
| Immune modulation | Stimulates macrophages, mast cell degranulation, T-cell proliferation | Bridges nervous and immune systems in inflammation |
| Mood/anxiety | CNS NK1 signaling involved in stress response and depression | NK1 antagonists showed antidepressant potential in some trials |
| Study | Design | Findings | Level |
|---|---|---|---|
| Aprepitant (Emend) | Phase III RCTs | NK1 antagonist prevents chemotherapy-induced nausea/vomiting; FDA-approved | Level I |
| Chronic pain | Extensive preclinical + clinical | SP elevated in chronic pain conditions; NK1 antagonists reduce pain in animal models but mixed clinical results | Level I-II (mixed) |
| Depression | Phase II/III trials | NK1 antagonists showed initial promise as antidepressants but failed in large Phase III trials | Level I (negative) |
| Inflammatory bowel disease | Preclinical + observational | SP elevated in IBD patients; SP-positive nerve fibers increased in inflamed gut tissue | Level II-III |
Substance P itself is not administered therapeutically: It is an endogenous neuropeptide. Clinical interest focuses on NK1 receptor antagonists that block its effects.
NK1 antagonists (aprepitant): Generally well-tolerated. Main side effects: fatigue, hiccups, constipation. Drug interactions via CYP3A4 inhibition.
| Jurisdiction | Status |
|---|---|
| FDA | Aprepitant (Emend) approved for chemotherapy-induced nausea (2003). Fosaprepitant (IV) also approved. |
| Research | SP itself is a research tool, not a therapeutic agent |