Peptide Schedule
Somatostatin (SST-14 and SST-28)14 residuesAGCKNFFWKTFTSCEach bubble = one amino acid. Size = residue mass. Color = chemical class.Somatostatin (SST-14 and SST-28)
Benefits
About Somatostatin (SST-14 and SST-28)
Somatostatin (somatotropin release-inhibiting factor, SRIF) is a cyclic peptide hormone first isolated from ovine hypothalamic extracts by Roger Guillemin's laboratory in 1973. It exists in two principal bioactive forms: SST-14, a 14-amino-acid cyclic peptide with a disulfide bridge between Cys3 and Cys14, and SST-28, an N-terminally extended 28-amino-acid form that includes the full SST-14 sequence at its C-terminus. Both forms are generated by proteolytic processing of a 116-amino-acid precursor, preprosomatostatin. Somatostatin is produced in multiple tissues throughout the body: hypothalamic neurons of the periventricular nucleus (where it acts as the primary inhibitor of pituitary growth hormone release), delta cells of the pancreatic islets (regulating insulin and glucagon secretion in a paracrine manner), and D cells scattered throughout the gastrointestinal mucosa (suppressing gastric acid, pepsin, gastrin, secretin, cholecystokinin, and other GI hormones). It also functions as a neurotransmitter in the central nervous system, with roles in cognition, pain modulation, and motor activity. The peptide binds to five G protein-coupled receptor subtypes (SSTR1 through SSTR5) with varying affinities. SST-14 binds all five subtypes with roughly equal affinity, while SST-28 shows preferential binding to SSTR5. These receptors are widely distributed across the brain, pituitary, pancreas, GI tract, immune cells, and various tumors — particularly neuroendocrine tumors that overexpress SSTR2. The critical limitation of native somatostatin is its ultrashort plasma half-life of approximately 1 to 3 minutes following intravenous administration, due to rapid enzymatic degradation by endopeptidases in blood and tissues. This necessitated the development of metabolically stable synthetic analogs: octreotide (half-life ~1.8 hours), lanreotide (half-life ~23-30 days for depot), and pasireotide (half-life ~12 hours), which selectively target subsets of somatostatin receptors with dramatically extended durations of action. Despite its impracticality as a therapeutic agent, native somatostatin remains an important research tool and has been used clinically in specialized settings, including continuous IV infusion for acute variceal hemorrhage (largely superseded by octreotide), diagnostic provocative testing for insulinoma, and investigational studies of hormone secretion physiology.
Who Should Consider Somatostatin (SST-14 and SST-28)
- Researchers studying somatostatin receptor pharmacology and signaling
- Endocrinologists performing diagnostic provocative tests (e.g., insulinoma workup)
- Clinical investigators studying GH regulation and pituitary physiology
- Gastroenterologists managing acute variceal bleeding (historical/specialized use)
- Neuroscience researchers studying CNS somatostatin pathways
- Pharmacologists developing novel somatostatin receptor-targeted therapeutics
How Somatostatin (SST-14 and SST-28) Works
Somatostatin exerts its biological effects by binding to five G protein-coupled somatostatin receptor subtypes (SSTR1 through SSTR5), all of which couple primarily to inhibitory G proteins (Gi/Go). SST-14 binds all five subtypes with approximately equal nanomolar affinity, while SST-28 demonstrates 10-fold higher selectivity for SSTR5. Upon ligand binding, the activated Gi/Go alpha subunit inhibits adenylyl cyclase, reducing intracellular cAMP and protein kinase A (PKA) activity. This is the primary antisecretory mechanism in pituitary somatotrophs (suppressing GH gene transcription and exocytosis) and pancreatic beta/alpha cells (inhibiting insulin and glucagon release). The Gi beta-gamma subunit simultaneously activates G protein-coupled inwardly rectifying potassium (GIRK) channels and inhibits voltage-gated calcium channels (N-type and L-type), leading to membrane hyperpolarization and reduced calcium-dependent exocytosis of hormone-containing secretory granules. Somatostatin receptors also engage non-canonical signaling pathways: SSTR2 and SSTR5 activate protein tyrosine phosphatases SHP-1 and SHP-2, which dephosphorylate key growth factor receptors and downstream signaling molecules, contributing to the antiproliferative and proapoptotic effects observed in tumor cells. SSTR1 and SSTR2 can also signal through phospholipase C (PLC) inhibition and activation of the MAPK cascade in a context-dependent manner. The rapid degradation of native somatostatin occurs through cleavage by ubiquitous endopeptidases, primarily at the Trp8-Lys9 bond and the Phe7-Trp8 bond within the disulfide-constrained ring. The synthetic analogs (octreotide, lanreotide) were engineered by incorporating D-amino acids and reducing the ring size to protect these cleavage sites while retaining SSTR2/SSTR5 selectivity.
What to Expect
Rapid onset of GH suppression and reduction of splanchnic blood flow. Peak plasma concentration achieved almost immediately with IV administration.
Plasma levels decline rapidly (half-life ~1-3 min). GH, insulin, and glucagon secretion are acutely suppressed. Gastric acid output decreases measurably.
Sustained suppression of GH, insulin, glucagon, and GI hormones for the duration of infusion. Steady-state plasma levels achieved within 10-15 minutes. Portal pressure reduction evident in variceal bleeding applications.
Rapid clearance from plasma. Rebound hypersecretion of GH and other hormones may occur within minutes of cessation. Blood glucose may fluctuate — monitor for rebound hypoglycemia or hyperglycemia.
All direct hormonal effects fully reversed. No residual activity expected beyond 15-30 minutes. Rebound GH elevation typically normalizes within 1-2 hours.
Dosing Protocol
| Level | Dose / Injection | Frequency |
|---|---|---|
| Beginner | 100mcg | Daily |
| Moderate | 250mcg | Daily |
| Aggressive | 500mcg | Daily |
Note: Somatostatin (SRIF, somatotropin release-inhibiting factor) is the endogenous cyclic peptide hormone produced in the hypothalamus, GI tract, and pancreatic delta cells. It exists in two bioactive forms: SST-14 (14 amino acids) and SST-28 (N-terminally extended 28 amino acids). Native somatostatin itself has an extremely short half-life of approximately 1-3 minutes IV, which renders it impractical for routine clinical use. This ultrashort duration of action is the primary reason synthetic analogs — octreotide, lanreotide, and pasireotide — were developed with engineered metabolic stability. Native somatostatin is primarily used in research settings and specialized diagnostic/provocative tests (e.g., somatostatin infusion test for insulinoma). The dosing tiers shown reflect research and diagnostic infusion protocols only. This peptide is NOT a standard therapeutic agent; patients requiring somatostatin-like therapy should use FDA-approved analogs. All use should be under direct medical supervision in a clinical setting.
How to Inject Somatostatin (SST-14 and SST-28)
Native somatostatin is administered almost exclusively via continuous intravenous infusion in hospital or research settings due to its 1-3 minute half-life. For diagnostic use: a bolus of 1-5 mcg/kg IV followed by continuous infusion at 1-5 mcg/kg/min. For acute variceal hemorrhage (historical use): 250 mcg IV bolus followed by 250-500 mcg/hour continuous infusion for up to 5 days. The peptide is typically supplied as a lyophilized powder and reconstituted in sterile normal saline or bacteriostatic water. Subcutaneous injection has been used in research settings but provides poor therapeutic utility due to rapid degradation. This is not a self-administered peptide — all use requires medical supervision with hemodynamic and glucose monitoring. Patients should be monitored for bradycardia and blood glucose fluctuations during and after infusion.
Cycling Protocol
Native somatostatin is not used in cycling protocols due to its ultrashort half-life. Research and diagnostic applications typically involve single-session continuous IV infusions lasting minutes to hours. For variceal hemorrhage, infusions of 250-500 mcg/hour are maintained for 2-5 days. There is no established cycling regimen. Patients requiring long-term somatostatin receptor suppression should use FDA-approved analogs (octreotide, lanreotide, or pasireotide) under medical supervision.
Pharmacokinetics
Source: Sheppard M et al. Multiple IV studies; SST-14 half-life 1-3 minutes (mean ~3 min). Patel YC. Front Neuroendocrinol. 1999;20(3):157-198. PMID: 10433861
Loading the interactive decay curve.
Side Effects
Due to the ultrashort half-life, side effects during brief IV infusion are generally transient. The most common effects include nausea, abdominal cramping, and diarrhea (due to suppressed GI motility and enzyme secretion). Hyperglycemia may occur from insulin suppression, though rebound hypoglycemia can follow infusion cessation as glucagon suppression lifts before insulin recovers. Bradycardia and mild hypotension have been noted during IV infusion. Flushing at the injection site is possible. With prolonged continuous infusion, the same risks seen with somatostatin analogs apply: gallbladder stasis and sludge formation, fat malabsorption (steatorrhea), and vitamin B12 deficiency. A notable rebound hypersecretion phenomenon can occur after somatostatin withdrawal, with transient overshooting of GH, insulin, and gastric acid levels. Pain at the IV infusion site is common during extended administration.
Contraindications
- Known hypersensitivity to somatostatin or any formulation component
- Severe cardiac conduction disorders (risk of bradycardia and arrhythmia)
- Type 1 diabetes with brittle glycemic control (risk of severe hypoglycemia upon withdrawal)
- Pregnancy and breastfeeding (insufficient safety data; avoid unless clearly necessary)
- Severe hepatic impairment (altered metabolism and unpredictable clearance)
- Pre-existing hypotension or hemodynamic instability (risk of further blood pressure reduction)
- Concurrent use of drugs with strong bradycardic effects without cardiac monitoring
Drug Interactions
- Insulin and oral hypoglycemics: Somatostatin suppresses both insulin and glucagon; blood glucose may become unpredictable; intensive monitoring required
- Beta-blockers: Additive bradycardia risk; continuous cardiac monitoring recommended during co-administration
- Calcium channel blockers (verapamil, diltiazem): Enhanced negative chronotropic effects; avoid combination without ECG monitoring
- Growth hormone therapy: Somatostatin directly antagonizes exogenous GH effects; concurrent use is pharmacologically counterproductive
- Cyclosporine: May reduce cyclosporine absorption and blood levels (documented with octreotide; likely applies to native somatostatin)
- QT-prolonging medications: Theoretical additive risk of cardiac arrhythmias given somatostatin's cardiac effects
Storage & Stability
Molecular Profile
Related Peptides
References
- Somatostatin and somatostatin receptors: from basic concepts to clinical applicationsReview
- Somatostatin, somatostatin analogues and somatostatin receptor dynamics in the biology of cancer progressionReview
- Hypothalamic somatostatin: discovery, notes on its discovery, and clinical usePubMed 18479298
- Somatostatin and the gastrointestinal tractReview
- Somatostatin infusion in the management of acute variceal hemorrhage: a systematic reviewPubMed 11207511
- Structural basis for somatostatin receptor 2 activation and signalingPubMed 35197637