Almost every discussion of growth hormone research peptides is about the accelerator. GHRH analogues push, ghrelin-receptor agonists push, blends push twice. Far less is said about the brake — and the brake is half the system. Somatostatin is the hypothalamic peptide that stops growth hormone being released, and because it sets the troughs between pulses, it shapes the pattern of growth hormone secretion as much as anything that stimulates it.
This guide covers what somatostatin is, how it was found, the receptor family it works through, what it does outside the pituitary, and why its short life in the bloodstream produced a family of engineered analogues. It also takes apart a claim that circulates constantly in peptide writing and is contradicted by the review usually cited for it.
The short answer
- Somatostatin is an inhibitory peptide hormone. It was isolated from ovine hypothalamus and reported in Science in 1973 as a polypeptide that inhibits the secretion of pituitary growth hormone.
- There are two bioactive forms from one precursor. A 116-residue preprosomatostatin is processed into somatostatin-28 and, within it, the 14-residue somatostatin-14, which carries a disulfide bridge between its third and fourteenth residues.
- It works through five G-protein-coupled receptors, SST1 to SST5, encoded by SSTR1–SSTR5. All of them signal through Gi/Go proteins and inhibit adenylyl cyclase, which is why the output is almost always “less of something”.
- It is not only a pituitary hormone. The same peptide is released by pancreatic delta cells and gastrointestinal D cells, where it restrains both insulin and glucagon.
- It survives minutes, not hours. Native somatostatin has a circulating half-life under three minutes, which is the whole reason engineered analogues exist.
- Those analogues are medicines. Octreotide, first described in 1982 as an eight-residue analogue with prolonged action, plus lanreotide and pasireotide, are prescription drugs used in acromegaly and neuroendocrine tumours. Somatostatin itself is not supplied by Pure Peptides Canada in any form.
- The common claim that GHRPs work by suppressing somatostatin is not supported. The review most often cited for it says the opposite: growth hormone secretagogues raise growth hormone without disturbing the feedback mechanisms that include somatostatin.
Somatostatin
SRIF · somatotropin release-inhibiting factor · growth hormone-inhibiting hormone
- Molecule type
- Inhibitory peptide hormone and neuropeptide
- Gene
- SST, human chromosome 3; precursor preprosomatostatin, 116 residues
- Bioactive forms
- Somatostatin-14 (residues 103–116 of the precursor) and somatostatin-28 (residues 89–116)
- Structure
- Cyclic; a disulfide bridge links the cysteines at precursor positions 105 and 116 — positions 3 and 14 of somatostatin-14
- Receptors
- SST1–SST5, five Gi/Go-coupled GPCRs; genes SSTR1–SSTR5 on chromosomes 14, 17, 22, 20 and 16
- Circulating half-life
- Under 3 minutes
- First reported
- 1973, by Brazeau and colleagues in Roger Guillemin’s laboratory
- In the catalogue
- Not stocked. This article is background for the growth-hormone-axis reagents it links to
Where the evidence stands
- Cell and animal studies
- Human physiology studies
- Analogues in clinical use
- Established textbook endocrinology
Somatostatin biology is settled science, not a frontier. What remains contested is the detail — which receptor does what in which tissue, and how pulse timing is generated.
What somatostatin is
Somatostatin is a small peptide whose job is to say no. Where most of the hormones in the growth-hormone story are releasing factors, somatostatin is a release-inhibiting factor, and its older name — somatotropin release-inhibiting factor, or SRIF — states that directly. It is both a hormone, carried in the blood, and a neuropeptide, released locally by neurons, which is a dual role it shares with several of the peptides covered in our guide to neuropeptides.
Two features explain most of its behaviour. The first is that it is cyclic: a disulfide bridge between two cysteine residues closes the peptide into a loop, which constrains its shape and is part of why a 14-residue molecule can bind receptors with high affinity. Our explainer on short peptides covers why length alone says little about what a peptide can do.
The second is that it is fast. Native somatostatin has a circulating half-life of under three minutes, as the 2018 IUPHAR review of the receptor family records. A hormone that disappears in minutes is well suited to moment-to-moment regulation and badly suited to being a drug, and that tension drove four decades of analogue chemistry.
How it was found
Somatostatin was found by accident, in the middle of a search for something else. Through the 1960s and early 1970s, Roger Guillemin’s laboratory at the Salk Institute was working through sheep hypothalamic extracts hunting for the factor that releases growth hormone. What they isolated first was a fraction that did the reverse.
The 1973 report in Science — “Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone”, by Brazeau, Vale, Burgus, Ling, Butcher, Rivier and Guillemin — describes a peptide isolated from ovine hypothalamus that at a concentration of one nanomolar inhibited secretion of immunoreactive rat or human growth hormone in vitro, with similar activity in rats in vivo. The paper gives the complete sequence, H-Ala-Gly-Cys-Lys-Asn-Phe-Phe-Trp-Lys-Thr-Phe-Thr-Ser-Cys-OH, and reports that the synthetic replicate was biologically active. That sequence contains fourteen residues, which is where the name somatostatin-14 comes from, though the paper itself does not use the number.
The growth-hormone-releasing factor they were originally looking for took another decade to pin down. When it arrived it became the parent molecule for the whole GHRH-analogue family — sermorelin, tesamorelin, CJC-1295 — covered in our growth hormone peptides research map.
Two peptides, one precursor
Somatostatin is made as a much larger protein and cut down. The human SST gene, on chromosome 3, encodes a 116-residue precursor called preprosomatostatin. Processing at different cleavage sites releases two different bioactive peptides from the same molecule, which UniProt’s curated entry for the human protein maps precisely: somatostatin-28 is residues 89 to 116, and somatostatin-14 is residues 103 to 116 — the last fourteen residues, sitting inside the longer form. The disulfide bridge is between the cysteines at precursor positions 105 and 116, which are positions 3 and 14 of somatostatin-14, matching the 1973 sequence exactly.
The longer form was characterised separately. Pradayrol and colleagues reported the primary structure of somatostatin-28 in FEBS Letters in 1980, describing it as N-terminally extended somatostatin — the same core with fourteen extra residues in front.
The two forms are not interchangeable in practice, because different tissues favour different ones. Somatostatin-14 is the form secreted by somatostatin-expressing neurons and pancreatic delta cells, while somatostatin-28 is the dominant form released from D cells of the gastrointestinal tract, as the 2021 review of islet delta cells sets out. Same gene, same core sequence, different distribution.
The five receptors
Somatostatin’s effects run through five receptors, and knowing which is which is the difference between understanding the pharmacology and guessing at it. All five are G-protein-coupled receptors — the class covered in our explainer on peptide receptors and GPCRs. All five associate with Gi/Go proteins, and the reduction in cyclic AMP that follows comes from inhibition of adenylyl cyclase. That shared inhibitory wiring is why a single hormone can suppress growth hormone, insulin, glucagon and gut secretions through five different receptors.
| Receptor | Gene and chromosome | What the literature associates it with |
|---|---|---|
| SST1 | SSTR1, chromosome 14 | A selective SST1 agonist decreased growth hormone secretion in wild-type mice, so the pituitary story is not purely SST2 and SST5 |
| SST2 | SSTR2, chromosome 17 | Growth-hormone-expressing pituitary cells almost completely colocalize with SST2. Also the main route for somatostatin’s effect on glucagon-secreting alpha cells. The preferred target of octreotide and lanreotide |
| SST3 | SSTR3, chromosome 22 | Reported to predominantly confer somatostatin-dependent inhibition of insulin secretion on beta cells, in both mouse and human islets |
| SST4 | SSTR4, chromosome 20 | The least exploited subtype pharmacologically; no clinically used analogue is built around it |
| SST5 | SSTR5, chromosome 16 | Together with SST2, the pathway behind octreotide’s suppression of growth hormone in people. Pasireotide’s highest affinity is here |
A naming trap worth knowing. The 2018 IUPHAR review recommends calling the receptor proteins SST1 to SST5 and explicitly discourages “SSTR1, SSTR2” for the receptors — while SSTR1 to SSTR5 remain the official gene symbols. So the gene is SSTR2 and the protein it makes is SST2. Most peptide writing uses the two interchangeably; a paper that is careful about it is usually careful about other things too.
One frequently repeated simplification is worth correcting here. It is often written that SST2 inhibits insulin release. The delta-cell review above assigns beta-cell insulin inhibition predominantly to SST3, and gives SST2 as the alpha-cell, glucagon-side route. The pituitary story (SST2 and SST5) and the islet story are different, and swapping them is a common error.
The brake on growth hormone
Growth hormone is not secreted at a steady rate. It comes in bursts, and the pattern is produced by two opposing hypothalamic inputs onto the pituitary somatotrophs: GHRH, which stimulates, and somatostatin, which inhibits. A 2025 review of GHRH neurons describes the balance of excitatory and inhibitory inputs that generate the pulsatile secretion pattern, notes that somatostatin neurons provide strong inhibitory control over both GHRH neuron activity and growth hormone secretion, and reads the troughs between pulses as periods of heightened inhibitory tone.
What the evidence does not settle is how the pulses are started. A popular account holds that growth hormone pulses are generated by somatostatin withdrawal — the brake coming off. The 2025 review does not say that, and at least two human studies have argued directly against it, including one whose title states that somatostatin withdrawal alone is an ineffective generator of pulsatile growth hormone release in man. We could not read those papers in full, so we flag the question as open rather than citing a result. The defensible statement is narrower: somatostatin tone is highest during troughs, and reciprocal GHRH and somatostatin input shapes the pattern.
The human pharmacology of the brake is better documented. Octreotide, a somatostatin analogue preferring SST2 and SST5, reduced mean eight-hour growth hormone concentrations in both young and older men in a 1999 study. In a 2004 study of ten healthy men given saline, GHRH, GHRP-2 or both, octreotide lowered fasting growth hormone and reduced secretory burst mass with GHRH, with GHRP-2, and with the two together. In other words the brake can override both kinds of accelerator.
Timing complicates even that. A 1994 study found that octreotide given eight or sixteen hours before a GHRH bolus did not affect the growth hormone response, but that octreotide given twelve hours before enhanced GHRH-induced release. Concurrent exposure suppresses; a prior exposure at the right interval can amplify. “Somatostatin blocks GHRH” is true acutely and false as a general rule.
The other job: islets and gut
Somatostatin is usually introduced through the pituitary, but a great deal of it never goes near the pituitary at all. In the pancreatic islet it is released by delta cells, the third major islet cell type alongside insulin-secreting beta cells and glucagon-secreting alpha cells, and the 2021 review describes it as a potent and fast inhibitor for both insulin and glucagon secretion. One peptide, acting locally, restraining both of the islet’s main outputs — which is why delta cells get described as the neighbourhood watch of the islet.
In the gastrointestinal tract, D cells release predominantly somatostatin-28 and restrain a long list of secretions and motility functions. This is the context in which somatostatin is best thought of not as a growth-hormone hormone that happens to appear elsewhere, but as a general-purpose inhibitory signal that the body reuses wherever something needs damping. For comparison with the opposite kind of gut-derived signal, see our explainers on ghrelin and on peptide hormones generally.
Why analogues exist
A hormone with a sub-three-minute half-life cannot be given as a medicine in its native form, and the history of somatostatin pharmacology is the history of fixing that. The landmark is a 1982 paper in Life Sciences by Bauer and colleagues at Sandoz, whose title describes SMS 201-995 as a very potent and selective octapeptide analogue of somatostatin with prolonged action. SMS 201-995 is octreotide. Shortening the molecule from fourteen residues to eight and stabilising it produced something with the binding profile of the hormone and a usable duration.
| Analogue | Receptor profile | Notes |
|---|---|---|
| Octreotide | SST2-preferring; described in human studies as a preferential SST2/SST5 agonist | First described 1982 as an octapeptide with prolonged action. The reference tool for suppressing growth hormone in human studies |
| Lanreotide | SST2-preferring | Classified alongside octreotide as an SST2-preferring ligand in the IUPHAR review |
| Pasireotide | Non-selective: binds SST1, SST2, SST3 and SST5, with highest affinity at SST5 | Deliberately broad, to reach tumours that do not respond to SST2-preferring agents |
| Radiolabelled analogues | SST2-directed in practice | Because many neuroendocrine tumours overexpress somatostatin receptors, an analogue carrying a radionuclide can be aimed at them. A 2026 meta-analysis of fourteen studies and 1,844 patients treated with 177Lu-labelled receptor radionuclide therapy reported a pooled disease control rate of 87.6% |
All of these are prescription medicines, prescribed for conditions such as acromegaly and neuroendocrine tumours. They are mentioned here because they are the reason somatostatin receptor pharmacology is as well mapped as it is — not as anything Pure Peptides Canada supplies or could supply. We stock no somatostatin and no somatostatin analogue.
The claim that does not hold up
If you read enough about growth hormone research peptides you will meet this sentence in some form: GHRPs, or ghrelin-receptor agonists such as ipamorelin, work partly by suppressing somatostatin. It sounds mechanistically tidy — push the accelerator and release the brake — and it is usually attributed to a 2018 review in Sexual Medicine Reviews, Sigalos and Pastuszak’s “The Safety and Efficacy of Growth Hormone Secretagogues”.
Somatostatin appears exactly once in that review, and what it says is the reverse. The sentence is that subsequent work found GHRPs act on both the pituitary and the hypothalamus, and that these peptides stimulate the release of growth hormone without affecting the normal negative feedback mechanisms in the growth hormone pathway that include somatostatin and IGF-1. Nowhere does the review state that GHRPs suppress, inhibit or reduce somatostatin.
We also found no primary source stating that ipamorelin specifically acts by suppressing somatostatin. There is older rodent work examining whether GHRH and somatostatin are involved in the actions of hexarelin and GHRP-6, and that literature exists — but it is not what the 2018 review says, and it is not about ipamorelin.
Why this matters beyond one sentence. A claim like this is cheap to repeat and expensive to check, so it propagates. It is a good example of the substitution our guide to reading a peptide study warns about: a plausible mechanism gets stated as a finding, and the citation attached to it turns out to say something different. If you see a somatostatin-suppression claim about any growth hormone secretagogue, the question to ask is which paper measured somatostatin, and in what species.
The honest version is less satisfying and more useful. GHRH analogues act on the GHRH receptor; ghrelin-receptor agonists act on the growth hormone secretagogue receptor; somatostatin acts on SST1–SST5. Three different receptor families. Our comparisons of CJC-1295 and ipamorelin and of sermorelin and ipamorelin work through what each class does and does not have evidence for.
What’s established and what isn’t
Reasonably well established
- Somatostatin was isolated from ovine hypothalamus and reported in 1973 as an inhibitor of pituitary growth hormone secretion, with its full 14-residue sequence.
- Somatostatin-14 and somatostatin-28 come from the same 116-residue precursor by processing at different sites.
- Five Gi/Go-coupled receptors, SST1–SST5, mediate its effects, and the fall in cyclic AMP follows inhibition of adenylyl cyclase.
- Native somatostatin’s circulating half-life is under three minutes.
- Octreotide suppresses growth hormone in people, including growth hormone stimulated by GHRH and by GHRP-2.
- Somatostatin inhibits both insulin and glucagon secretion in the islet.
- Somatostatin tone is highest during the troughs between growth hormone pulses.
Open questions
- Whether somatostatin withdrawal initiates growth hormone pulses. The 2025 review does not say so, and human studies have argued against it; we could not read those in full.
- Exactly which receptor subtypes carry which pituitary effect. SST2 and SST5 dominate the pharmacology, but an SST1-selective agonist also lowered growth hormone in mice, so “only SST2 and SST5” overstates it.
- Whether the SST3 assignment for beta-cell insulin inhibition holds across species and preparations.
- Why octreotide’s effect on GHRH-stimulated growth hormone reverses sign depending on the interval between the two.
- Whether any of the growth hormone secretagogues sold as research reagents interact with somatostatin signalling at all. No primary source we reached shows that they do.
- What SST4 is for. It is the one subtype with no analogue built around it.
Sourcing growth-hormone-axis reagents in Canada
Somatostatin itself is not a research reagent we supply, so the practical sourcing questions here concern the compounds on the stimulating side of the axis. Those are peptides, and the documentation standards are the ordinary ones.
- Check purity and identity separately. HPLC tells you how much of the material is the peak you want; mass spectrometry tells you whether that peak is the right molecule. See our guides to reading an HPLC chromatogram and reading a mass spectrum.
- Match the batch number on the certificate to the number on the vial. Our COA guide covers what else a useful certificate contains and how to spot one that is not genuine.
- Remember that labelled mass is not peptide mass. Synthetic peptides arrive as salts with counter-ions and bound water. Our guide to net peptide content works through the arithmetic.
- Keep material cold, dry and dark, and lyophilized until the point of use — see the storage guide, what lyophilized means and how peptides degrade. Cyclic, disulfide-containing peptides have their own failure mode: the bridge can scramble or reduce.
SermorelinThe 29-residue GHRH fragment — the releasing side of the axisView product
CJC-1295 with DACA long-acting GHRH analogueView product
IpamorelinA ghrelin-receptor agonist, not a somatostatin ligandView product
HexarelinA GHRP, the class the older somatostatin-involvement work usedView product
Research use only. Pure Peptides Canada products are laboratory reagents for in-vitro research, not for human or veterinary use. This article explains published research for education; it is not medical, dietary or dosing guidance.
Frequently asked questions
What is somatostatin?
Somatostatin is an inhibitory peptide hormone, also known as somatotropin release-inhibiting factor. It was isolated from ovine hypothalamus and reported in Science in 1973 as a polypeptide that inhibits the secretion of pituitary growth hormone. It exists in two bioactive forms, somatostatin-14 and somatostatin-28, both cut from the same 116-residue precursor, and it acts through five G-protein-coupled receptors.
What does somatostatin do to growth hormone?
It inhibits its release. Growth hormone is secreted in pulses, and the pattern comes from two opposing hypothalamic inputs onto the pituitary: GHRH, which stimulates, and somatostatin, which inhibits. Somatostatin tone is highest during the troughs between pulses. In human studies, the somatostatin analogue octreotide reduced growth hormone secretory burst mass even when growth hormone had been stimulated by GHRH, by GHRP-2, or by both together.
What is the difference between somatostatin-14 and somatostatin-28?
They are the same core peptide at different lengths, processed from one precursor at different cleavage sites. Somatostatin-14 is the last fourteen residues of preprosomatostatin; somatostatin-28 is the last twenty-eight, so it is somatostatin-14 with an N-terminal extension. Tissues differ in which they release: somatostatin-14 is the form from somatostatin-expressing neurons and pancreatic delta cells, while somatostatin-28 is the dominant form from D cells of the gastrointestinal tract.
How many somatostatin receptors are there?
Five. They are named SST1 to SST5 and encoded by the genes SSTR1 to SSTR5, on human chromosomes 14, 17, 22, 20 and 16 respectively. All five are G-protein-coupled receptors that associate with Gi/Go proteins, and the drop in cyclic AMP that follows comes from inhibition of adenylyl cyclase. The 2018 IUPHAR review recommends SST1 to SST5 for the receptor proteins and discourages using the gene-style names for them.
Why were somatostatin analogues developed?
Because native somatostatin has a circulating half-life of under three minutes, which makes it unusable as a medicine. The first successful answer was described in 1982: SMS 201-995, now called octreotide, a very potent and selective octapeptide analogue with prolonged action. Lanreotide, like octreotide, prefers the SST2 receptor; pasireotide binds SST1, SST2, SST3 and SST5, with its highest affinity at SST5.
Do GHRPs or ipamorelin work by suppressing somatostatin?
Not according to the review usually cited for that claim. Sigalos and Pastuszak’s 2018 review mentions somatostatin once, and says that GHRPs act on both the pituitary and the hypothalamus and stimulate growth hormone release without affecting the normal negative feedback mechanisms in the pathway that include somatostatin and IGF-1. We found no primary source stating that ipamorelin in particular acts by suppressing somatostatin.
Does Pure Peptides Canada sell somatostatin?
No. We stock no somatostatin and no somatostatin analogue. This article is background for the growth-hormone-axis research reagents we do supply, which all act on the stimulating side of the axis: sermorelin and CJC-1295 at the GHRH receptor, and ipamorelin and hexarelin at the growth hormone secretagogue receptor. Those are supplied only as laboratory reagents for in-vitro research.
Growth-hormone-axis reagents, documented by batch
Sermorelin, CJC-1295, ipamorelin and the rest of the growth and signalling range, priced in Canadian dollars and shipped tracked from inside Canada.
References
- Brazeau P, Vale W, Burgus R, Ling N, Butcher M, Rivier J, Guillemin R. Hypothalamic polypeptide that inhibits the secretion of immunoreactive pituitary growth hormone. Science. 1973;179(4068):77–79. DOI
- Pradayrol L, Jörnvall H, Mutt V, Ribet A. N-terminally extended somatostatin: the primary structure of somatostatin-28. FEBS Lett. 1980;109(1):55–58. DOI
- Bauer W, Briner U, Doepfner W, Haller R, Huguenin R, Marbach P, Petcher TJ, Pless J. SMS 201-995: a very potent and selective octapeptide analogue of somatostatin with prolonged action. Life Sci. 1982;31(11):1133–1140. DOI
- Valcavi R, Zini M, Maestroni GJ, Conti A, Portioli I. Octreotide administration, under particular temporal conditions, enhances the responses of growth hormone to growth hormone-releasing hormone in normal subjects. Clin Endocrinol (Oxf). 1994;40(3):379–382. DOI
- Mulligan T, Jaen-Vinuales AV, Godschalk M, Iranmanesh A, Veldhuis JD. Synthetic somatostatin analog (octreotide) suppresses daytime growth hormone secretion equivalently in young and older men. J Am Geriatr Soc. 1999;47(12):1422–1424. DOI
- Iranmanesh A, Bowers CY, Veldhuis JD. Activation of somatostatin-receptor subtype-2/-5 suppresses the mass, frequency, and irregularity of growth hormone (GH)-releasing peptide-2-stimulated GH secretion in men. J Clin Endocrinol Metab. 2004;89(9):4581–4587. DOI
- Sigalos JT, Pastuszak AW. The safety and efficacy of growth hormone secretagogues. Sex Med Rev. 2018;6(1):45–53. DOI
- Günther T, Tulipano G, Dournaud P, Bousquet C, Csaba Z, Kreienkamp H-J, Lupp A, Korbonits M, Castaño JP, Wester H-J, Culler M, Melmed S, Schulz S. International Union of Basic and Clinical Pharmacology. CV. Somatostatin receptors: structure, function, ligands, and new nomenclature. Pharmacol Rev. 2018;70(4):763–835. DOI
- Gao R, Yang T, Zhang Q. δ-Cells: the neighborhood watch in the islet community. Biology. 2021;10(2):74. DOI
- Jamieson BB. The gatekeepers of growth: the neural roles and regulation of growth hormone-releasing hormone neurons. J Neuroendocrinol. 2025;38(1):e70117. DOI
- Wang J, Pang X, Lian J, Lu H. 177Lu-labelled peptide receptor radionuclide therapy in patients with neuroendocrine tumors: a systematic review and meta-analysis. Front Endocrinol. 2026;17:1758639. DOI
- UniProt Consortium. UniProtKB entry P61278 (SMS_HUMAN), human somatostatin, including the 116-residue precursor and the somatostatin-14 and somatostatin-28 peptide boundaries.
For laboratory research use only. Not for human or veterinary use. This article summarizes published research for educational purposes and is not medical advice.