Somatostatin 

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Somatostatin is a polypeptide that is released in the gastrointestinal tract by delta cells and the hypothalamus. It functions as a key regulatory peptide that has many physiologic effects as an inhibitor for many other hormones, including gastrin, cholecystokinin, glucagon, growth hormone, insulin, secretin, pancreatic polypeptide, vasoactive intestinal peptide, 5-HT, and some pituitary hormones.

The reference range for plasma somatostatin in adults is 10-22 pgmL, the conversion factor is 0.426, and the SI units are 4.26-9.37 pmolL. Draw in prechilled tube, separate plasma, and freeze immediately. [1]

Serum and cerebrospinal fluid (CSF) somatostatin values less than 100 pg/mL are within normal limits for healthy individuals. Decreased levels have been found to be seen in CSF in autopsy samples of people with Alzheimer disease. [2] No change was found in normal, younger subjects to suggest that this could be a predisposing laboratory screen for patients. CSF values were also found to be elevated in young patients with febrile seizures. [3] Elevations in serum somatostatin are seen in somatostatinomas and neuroendocrine tumors. The levels are found to be on the scale of nanograms per milliliter, which is nearly 1000-fold greater than the standard unit. These tumors are very rare and slow-growing, but most patients are symptomatic. The following is the classic pentad of symptoms seen in a somatostatinoma syndrome: [4]

Diabetes mellitus

Cholelithiasis

Weight loss

and

Hypochlorhydria and achlorhydria

See the list below:

Specimen: Plasma

Condition: Fasting

Container: Lavender (EDTA; see image below) or pink (K EDTA) pre-chilled tube

Collection method: Routine venipuncture

Processing: Separate plasma from cells within 2 hours of collection in lab; an adequate sample requires a minimum of 0.6-1.8 mL. If multiple samples need to be analyzed, the specimen should be kept frozen. Ambient temperatures and exposure to room air will make sample unacceptable for analysis. [5]

See the list below:

Specimen: CSF

Collection method: Lumbar puncture

Typically part of same panel as CSF cell count, gram stain, albumin, glucose

Somatostatin is a polypeptide that is released in the gastrointestinal tract by delta cells and the hypothalamus. It functions as a key regulatory peptide that has many physiologic effects as an inhibitor for many other hormones, including gastrin, cholecystokinin, glucagon, growth hormone, insulin, secretin, pancreatic polypeptide, vasoactive intestinal peptide, 5-HT, and some pituitary hormones.

“The clinical usefulness of somatostatin is limited by its short half-life in the circulation (3 minutes) when it is administered by intravenous injection.” [6] Therefore, a synthetic preparation, octreotide, is used that mimics the properties of somatostatin. Octreotide is an octapeptide that can be given intravenously (30 min), subcutaneously (6-12 hours), or intramuscularly (monthly) for various applications. The most common indications for use include imaging for somatostatinomas, other neuroendocrine tumors, variceal bleeding, refractory , and hypoglycemia. [6]

Gardner DG, Shoback D. Appendix: Normal Hormone Reference Ranges. Gardner DG, Shoback D, eds. Greenspan’s Basic & Clinical Endocrinology. http://www.accessmedicine.com/content.aspx?aID=8410499. Accessed April 10, 2012. 9th ed. New York: McGraw-Hill; 2011.

Raskind MA, Peskind ER, Lampe TH, Risse SC, Taborsky GJ Jr, Dorsa D. Cerebrospinal fluid vasopressin, oxytocin, somatostatin, and beta-endorphin in Alzheimer’s disease. Arch Gen Psychiatry. 1986 Apr. 43(4):382-8. [Medline].

Hirai K, Seki T. Cerebrospinal fluid somatostatin levels in febrile seizures and epilepsy in children. Neuropeptides. 2000 Feb. 34(1):18-24. [Medline].

Krejs GJ, Orci L, Conlon JM, Ravazzola M, Davis GR, Raskin P. Somatostatinoma syndrome. Biochemical, morphologic and clinical features. N Engl J Med. 1979 Aug 9. 301(6):285-92. [Medline].

National Reference Laboratories. Somatostatin: ARUP Lab Tests. ARUP Laboratories:. Available at http://www.aruplab.com. Accessed: 2006-2012.

McQuaid KR. Drugs Used in the Treatment of Gastrointestinal Diseases. Accessed April 10, 2012. Katzung BG, Masters SB, Trevor AJ, eds. Basic & Clinical Pharmacology. 12nd ed. New York: McGraw-Hill; 2012. Chapter 62. [Full Text].

Cory Wilczynski, MD Fellow, Department of Endocrinology, Loyola Medical Center

Disclosure: Nothing to disclose.

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

Somatostatin 

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