Measurement of somatostatin is used primarily in the diagnosis of a very rare endocrine tumor called somatostatinoma. The tumor originates in the pancreas or gastrointestinal tract and produces excess amounts of somatostatin.
Somatostatin is a cyclic peptide well known for its strong regulatory effects throughout the body. Also known by the name of growth hormone inhibiting hormone, it is produced in many locations, which include the gastrointestinal (GI) tract, pancreas, hypothalamus, and central nervous system (CNS). Two active forms of the peptide exist, and they are different in size, with 14 amino acids and 28 amino acids, respectively. The two isoforms have considerable overlap in activity and differ primarily in their location of effect. The shorter isoform (14 amino acids) works primarily in the brain, while the longer (28 amino acids) form operates in the GI tract.
Somatostatin produces predominantly neuroendocrine inhibitory effects across multiple systems. It is known to inhibit GI, endocrine, exocrine, pancreatic, and pituitary secretions, as well as modify neurotransmission and memory formation in the CNS. It also prevents angiogenesis and has antiproliferative effects on healthy and cancerous cells in human and animal models.
Somatostatinoma can occur randomly or in association with certain genetic syndromes, including:
- Multiple endocrine neoplasia (MEN) type 1: This is a rare genetic condition in which multiple tumors affect different aspects of the endocrine system
- Neurofibromatosis type 1 (NF1): This is an inherited condition that causes cafe-au-lait spots (flat patches of light brown or coffee-colored skin) and benign tumors
- Von Hippel-Lindau disease: This is a rare inherited condition that can cause benign or malignant tumors in the brain, spinal cord, eyes, kidneys, pancreas, and adrenal glands
Excess somatostatin results in an extreme reduction of the release of many other hormones. Symptoms can be similar to symptoms of many other conditions, so somatostatinoma can be difficult to diagnose.