Octreotide is a synthetic analogue of somatostatin. It is a derivative of the natural hormone somatostatin and has similar pharmacological effects, but a much longer duration of action. Octreotide suppresses the secretion of growth hormone (GH), both pathologically elevated, and caused by arginine, exercise and insulin hypoglycemia. The drug also inhibits the secretion of insulin, glucagon, gastrin, serotonin, both pathologically elevated and caused by food intake; also inhibits the secretion of insulin and glucagon, stimulated by arginine. Octreotide suppresses the secretion of thyrotropin, caused by thyroidiberin.
In contrast to somatostatin, octreotide suppresses the secretion of GH more than insulin secretion, and its administration is not accompanied by subsequent hypersecretion of hormones (eg, GH in patients with acromegaly). In patients with acromegaly octreotide reduces the concentration of GH and insulin-like growth factor (IGF-1) in blood plasma.Reducing the concentration of GH by 50% or more is observed in 90% of patients, with a GH concentration of less than 5 ng / ml achieved in about half of the patients. In most patients with acromegaly octreotide reduces the severity of headache, soft tissue swelling, hyperhidrosis, joint pain and paresthesia. In patients with large adenomas of the pituitary gland, treatment with octreotide can lead to some reduction in tumor size.
With the secreting tumors of the gastroenteropancreatic endocrine system in cases of insufficient effectiveness of the therapy (surgical intervention, embolization of the hepatic artery, chemotherapy, including streptozotocin and fluorouracil), the administration of octreotide may lead to an improvement in the course of the disease. Thus, with carcinoid tumors, the use of octreotide can lead to a decrease in the intensity of the sensation of "tides" of blood to the face, diarrhea, which in many cases is accompanied by a decrease in serotonin concentration in the plasma and excretion of 5-hydroxyindoleacetic acid by the kidneys. In tumors characterized by hyperproduction of the vasoactive intestinal peptide (VIPoma),the use of octreotide leads in most patients to reduce severe secretory diarrhea and, accordingly, to improve the quality of life of the patient. At the same time, there is a decrease in associated electrolyte imbalance, for example, hypokalemia, which allows to cancel enteral and parenteral administration of fluid and electrolytes. Some patients slow or stop the progression of the tumor, there is a decrease in its size, as well as the size of metastases in the liver. Clinical improvement is usually accompanied by a decrease in the concentration of vasoactive intestinal peptide (VIP) in the plasma or its normalization. With glucagonomes, the use of octreotide leads to a decrease in migrating erythema. Octreotide does not have any significant effect on the severity of hyperglycemia in diabetes mellitus, while the need for insulin or oral hypoglycemic drugs usually remains unchanged. The drug causes a decrease in diarrhea, which is accompanied by an increase in body weight. Although the decrease in glucagon concentration in blood plasma under the influence of octreotide is transient, the clinical improvement remains stable throughout the period of application of the drug.In patients with gastrinomas / Zollinger-Ellison syndrome with octreotide in the form of monotherapy or in combination with proton pump inhibitors or H blockers2-gistaminovyh receptors may reduce hypersecretion of hydrochloric acid in the stomach, a decrease in the concentration of gastrin in the blood plasma, as well as a decrease in the severity of diarrhea and hot flashes. In patients with insulinomas octreotide reduces the level of immunoreactive insulin in the blood (this effect can be short-term - about 2 hours). In patients with operable tumors octreotide can provide recovery and maintenance of normoglycemia in the preoperative period. In patients with inoperable benign and malignant tumors, the control of glycemia can be improved without a simultaneous prolonged decrease in the concentration of insulin in the blood.
In patients with rare tumors, hyper-producing growth hormone releasing factor (somatoliberinomas), octreotide reduces the severity of symptoms of acromegaly. This is due to the suppression of the secretion of the growth hormone releasing factor and the GH itself. In the future, the pituitary gland hypertrophy may decrease.
With refractory diarrhea in patients with acquired immunodeficiency syndrome (AIDS), the use of octreotide results in complete or partial normalization of the stool in about 1/3 of patients with diarrhea not controlled by adequate antimicrobial and / or anti-diarrhea drugs.
In patients with pancreas surgery, the use of octreotide during and after surgery reduces the incidence of typical postoperative complications (eg pancreatic fistula, abscesses, sepsis, postoperative acute pancreatitis).
When bleeding from varicose veins in the esophagus and stomach of patients with liver cirrhosis octreotide application in combination with a specific treatment (for example, sclerosing therapy) results in a more efficient hemostasis and early rebleeding transfusion volume reduction and improvement of the 5-day survival. It is believed that the mechanism of action of octreotide is associated with a decrease in organ blood flow by suppressing such vasoactive hormones as VIP and glucagon.