Endogenous hormone and baseline drug
Natural somatostatin is produced in the hypothalamus, where its main task is to inhibit the secretion of growth hormone (GH) by the pituitary gland. Additionally, it is synthesized by D-cells of the gastric mucosa and pancreas, acting as a local (paracrine) inhibitor of digestive juice secretion.
In medicine, a synthetic cyclic tetradecapeptide analogue is used — Somatostatin.
- Pharmacodynamics: The drug acts selectively on hemodynamics. It significantly reduces blood flow velocity in the splanchnic arteries (splanchnic blood flow) and decreases internal organ congestion. A crucial clinical feature is the absence of significant surges in systemic arterial blood pressure (BP).
- Pharmacokinetics: Characterized by an extremely short half-life ($t_{1/2}$ of only 2–6 minutes). This is due to the rapid degradation of the peptide by plasma enzymes (aminopeptidases and endopeptidases). Administered exclusively by intravenous drip infusion.
- Indications: Cessation of bleeding from esophageal varices, prevention of complications in pancreatic surgery, and conservative treatment of fistulas (intestinal, biliary, and pancreatic).
- Side effects: Bradycardia, dizziness, facial flushing, as well as dyspeptic disorders (nausea and vomiting).
Octreotide — prolonged octapeptide
Octreotide is a synthetic octapeptide analogue. By modifying the molecular structure, a significant prolongation of the effect has been achieved: the drug acts for about 12 hours, and its half-life is approximately 100 minutes. Administered parenterally (subcutaneously or intravenously).
The increased duration of action has significantly expanded the spectrum of indications:
- Acromegaly: Octreotide suppresses GH secretion. It is prescribed when surgical treatment is impossible, or when dopamine receptor agonists are ineffective.
- Secreting tumors and GI pathologies: Used for gastrinoma, glucagonoma, carcinoid, and severe peptic ulcer disease to potently suppress the secretory activity of glandular tissue.
- Esophageal variceal bleeding: Particularly relevant for patients with liver cirrhosis (both for acute management and recurrence prevention).
Adverse reactions to octreotide include gastrointestinal disturbances (diarrhea, nausea, vomiting), liver function abnormalities, and plasma glucose fluctuations. Long-term use increases the risk of cholelithiasis (gallstone formation). The drug is contraindicated in hypersensitivity, pregnancy, and lactation.
Lanreotide — ultra-long-acting drug
For the treatment of chronic conditions requiring continuous secretion suppression, Lanreotide was developed.
- Pharmacokinetics: Possesses an even more pronounced prolonged action compared to its predecessor octreotide. Its half-life reaches 2.7–7.7 days.
- Dosing regimen: Administered intramuscularly only once every 10–14 days, which significantly reduces the injection burden on the patient.
Briefly: answers to topical questions
Which hormones, besides growth hormone, does endogenous somatostatin inhibit?
Endogenous somatostatin, in addition to growth hormone, inhibits a number of pancreatic and pituitary hormones. These include:
- Insulin — a hormone that lowers blood glucose levels.
- Glucagon — a hormone that raises blood glucose levels.
- Adrenocorticotropic hormone (ACTH) — an adenohypophyseal hormone.
- Thyroid-stimulating hormone (TSH) — a hormone that stimulates the thyroid gland.
Which synthetic analogues of somatostatin are used in medicine, apart from octreotide and lanreotide?
In addition to octreotide and lanreotide, sources mention:
- Somatostatin (drug Stilamin) — a synthetic cyclic tetradecapeptide analogue; used to stop bleeding from esophageal varices, prevent postoperative complications in pancreatic surgery, and treat pancreatic, intestinal, and biliary fistulas. Very short-acting: t1/2 is 2–6 minutes.
- 68Ga-DOTATOC — a somatostatin analogue used in PET imaging of meningiomas, as they have a high density of somatostatin receptors.
To remember the evolution of these drugs, use the "lengthening" rule: Somatostatin — Seconds/minutes (IV drip), Octreotide — Overnight (hours, subcutaneous), Lanreotide — Lunar cycles (weeks, intramuscular).
Class and exam questions
Why is somatostatin not used in tablet form?
The peptide structure of the drug is instantly destroyed by gastrointestinal enzymes. Even in blood plasma, it breaks down under the action of endopeptidases and aminopeptidases within 2–6 minutes, which is why it is administered solely by intravenous drip.
How does somatostatin stop bleeding from esophageal varices?
It selectively constricts the splanchnic arteries and reduces internal organ congestion. Meanwhile, systemic arterial blood pressure remains stable, which is critically important for critically ill patients with liver cirrhosis.
How does octreotide fundamentally differ from somatostatin?
Octreotide is a shortened (octapeptide) analogue. Due to structural modifications, it has become more resistant to enzymes: its action lasts about 12 hours, allowing subcutaneous administration and treatment of chronic diseases (e.g., acromegaly).
What specific risks are associated with long-term therapy using somatostatin analogues?
Due to the persistent suppression of the secretory activity of glandular tissue and biliary tract motility, long-term use of octreotide and lanreotide significantly increases the risk of cholelithiasis (gallstone formation) and causes fluctuations in plasma glucose levels.
What else to study on this topic
- Mechanisms of paracrine regulation by D-cells of the gastric mucosa and pancreas.
- Pathogenesis of esophageal variceal bleeding in liver cirrhosis.
- Principles of conservative therapy for acromegaly: the role of dopamine receptor agonists.
- Secreting GI tumors (gastrinoma, glucagonoma, carcinoid) and their impact on metabolism.
- Mechanism of gallstone formation (cholelithiasis) during prolonged secretion suppression.
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