Substance P is an 11-amino acid neuropeptide belonging to the tachykinin family. It was first discovered in 1931 by Ulf von Euler and John H. Gaddum as a potent hypotensive and smooth muscle-stimulating substance extracted from equine brain and intestine. Its name derives from its initial isolation as a ‘powder’ (P for powder). Substance P is encoded by the TAC1 gene and is one of the most extensively studied neuropeptides in mammalian physiology. It functions as a neurotransmitter and neuromodulator, playing a crucial role in pain signaling, neurogenic inflammation, and various autonomic and behavioral processes. Its significance lies in its central involvement in nociception, its role as a primary mediator of neurogenic inflammation, and its interactions with the immune and gastrointestinal systems.
Quick Facts
| Also Known As | SP, Tachykinin 1, Neurokinin 1, NK-1, Neurokinin P |
|---|---|
| Sequence | Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 |
| Molecular Formula | C63H98N18O13S |
| Molecular Weight | 1347.6 Da |
| PubChem CID | 36511 |
Research Parameters
| Half-Life | Very short, estimated at ~1-2 minutes in plasma due to rapid enzymatic degradation by peptidases like neutral endopeptidase (NEP) and angiotensin-converting enzyme (ACE). |
|---|---|
| Stability | Lyophilized powder is stable for at least 24 months when stored at -20°C, protected from light and moisture. After reconstitution in a suitable solvent (e.g., acetic acid solution or sterile saline), it should be aliquoted and stored at -20°C or below to prevent degradation; repeated freeze-thaw cycles should be avoided. Stability in solution at 4°C is limited to a few days. |
| Solubility | Recommended reconstitution in 0.1% acetic acid in water or sterile saline. It is also soluble in dimethyl sulfoxide (DMSO) for stock solutions, which can then be diluted in aqueous buffers. |
| Vial Size | 1 mg |
| Storage (Lyophilized) | -20°C or below, desiccated, protected from light. |
| Storage (Reconstituted) | -20°C or below in aliquots; avoid repeated freeze-thaw cycles. Use immediately for best results in sensitive assays. |
| Typical Research Dose | Not standardized for human research. In animal research, typical doses range from 1-10 mcg/kg for systemic effects, but are often administered in nmol amounts (e.g., 1-5 nmol, which is approximately 1.3-6.7 mcg for the peptide) for central or localized administration. |
| Cycle Parameters | Not applicable. Substance P research typically involves acute, single-dose administration protocols to study immediate physiological responses (e.g., pain behavior, inflammation) rather than chronic cycling protocols. |
| Amino Acid Count | 12 |
Mechanism of Action
Substance P exerts its biological effects primarily by binding to and activating the neurokinin-1 receptor (NK-1R), a G-protein coupled receptor. This binding triggers intracellular signaling cascades that mediate its diverse physiological and pathophysiological roles. The primary signaling pathway involves the activation of phospholipase C (PLC), leading to the generation of inositol trisphosphate (IP3) and diacylglycerol (DAG), which subsequently increase intracellular calcium and activate protein kinase C (PKC).
Pain Transmission and Nociception: Substance P is a key neurotransmitter released from the central terminals of primary afferent nociceptors (C-fibers) in the dorsal horn of the spinal cord. It facilitates pain transmission by depolarizing second-order neurons, enhancing the response to glutamate, and promoting central sensitization (wind-up).
Neurogenic Inflammation: Released from peripheral terminals of sensory neurons in response to injury or irritants, Substance P acts on NK-1 receptors on endothelial cells, mast cells, and immune cells. This causes vasodilation, plasma extravasation, and the recruitment and activation of leukocytes, contributing to inflammation.
Emotional and Behavioral Regulation: In the central nervous system, particularly in limbic structures like the amygdala and hypothalamus, Substance P modulates stress responses, anxiety, and depression. NK-1 receptor antagonists have been investigated for their antidepressant and anxiolytic effects.
Gastrointestinal Motility and Secretion: In the enteric nervous system, Substance P acts as an excitatory neurotransmitter, stimulating smooth muscle contraction, increasing intestinal secretion, and modulating peristalsis.
Interaction with Immune System: Substance P can modulate immune function by stimulating cytokine release (e.g., IL-1, TNF-α, IL-6) from macrophages and lymphocytes, and promoting T-cell proliferation, linking the nervous and immune systems.
Research Applications
Pain Research: Substance P is a fundamental model peptide for studying the neurobiology of pain, particularly chronic pain states like neuropathic pain and migraine. Research focuses on understanding central sensitization and developing NK-1 receptor antagonists as novel analgesics.
Inflammation and Immunology: Investigations explore its role as a mediator of neurogenic inflammation in conditions such as asthma, inflammatory bowel disease, rheumatoid arthritis, and psoriasis. Studies examine how neuro-immune interactions exacerbate or modulate inflammatory responses.
Psychiatry and Neurology: Research assesses the involvement of Substance P in stress-related disorders, major depression, and anxiety. Clinical trials have evaluated NK-1 receptor antagonists as potential antidepressants and anti-emetics, particularly for chemotherapy-induced nausea.
Gastroenterology: Studies investigate its role in regulating gut motility, secretion, and visceral hypersensitivity, relevant to disorders like irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).
Oncology Research: Substance P has been studied for its role in cancer progression, as it can promote angiogenesis, cell proliferation, and metastasis in some tumors. Conversely, Substance P conjugated to cytotoxic agents is explored for targeted cancer therapy due to the overexpression of NK-1 receptors on certain cancer cells.
Dermatology: Research focuses on its contribution to inflammatory skin conditions like psoriasis and atopic dermatitis, where it influences itch (pruritus) and neurogenic inflammation.
Safety & Side Effects
As an endogenous neurotransmitter, Substance P itself is not typically administered therapeutically. Safety data primarily come from studies of its physiological effects and from research on NK-1 receptor antagonists. Based on its known actions, theoretical or research-induced effects from exogenous administration could include: localized flushing, edema, and pain at injection site (due to neurogenic inflammation); hypotension; increased gastrointestinal motility and secretion; and potential exacerbation of inflammatory conditions. In central administration studies in animals, it can induce behavioral changes such as grooming and scratching. There are no established chronic toxicity profiles for exogenous Substance P administration. Anecdotal reports from research contexts are extremely limited.
Dosage Information
Disclaimer: The following information is derived from preclinical animal and human research studies only. It does not constitute dosing guidelines for human use.
In research settings, administration varies widely by model. In animal studies (e.g., rodents), Substance P is often administered via intracerebroventricular (ICV), intrathecal, or subcutaneous routes to study central and peripheral effects. Doses range from nanomolar to micromolar concentrations per injection (e.g., 1-10 nmol ICV in rats). In limited human experimental studies involving intradermal or topical application to induce local inflammation, doses are in the picomole to nanomole range. Frequency is typically acute or short-term bolus administration to elicit a specific physiological response, rather than chronic dosing protocols.
References
Pernow, B. Substance P. Pharmacological Reviews, 1983, 35(2), 85-141.
Maggi, C.A. The mammalian tachykinin receptors. General Pharmacology, 1995, 26(5), 911-944.
O'Connor, T.M., et al. The role of substance P in inflammatory disease. Journal of Cellular Physiology, 2004, 201(2), 167-180.
De Felipe, C., et al. Altered nociception, analgesia and aggression in mice lacking the receptor for substance P. Nature, 1998, 392(6674), 394-397.
Kramer, M.S., et al. Distinct mechanism for antidepressant activity by blockade of central substance P receptors. Science, 1998, 281(5383), 1640-1645.
Steinhoff, M.S., et al. Tachykinins and their receptors: contributions to physiological control and the mechanisms of disease. Physiological Reviews, 2014, 94(1), 265-301.
Harrison, S., & Geppetti, P. Substance P. The International Journal of Biochemistry & Cell Biology, 2001, 33(6), 555-576.