The peptide hormone somatostatin is a hormone present in vertebrates. It is secreted by the pancreas during digestion and by the hypothalamus. Somatostatin slows the production of the growth hormone somatotropin and is considered an important regulator in the overall hormonal system.
What is somatostatin?
Somatostatin is a peptide hormone that plays an essential role in many endocrine fields of action. In the past, it was also referred to as bulbogastron in the literature. Today, due to its inhibitory effect, this hormone also has the synonyms: SIH (somatotropin-inhibitory hormone) or GHRIH (growth hormone release inhibiting hormone). It is secreted in small amounts by the pancreas during digestion. Somatostatin is produced in many other parts of the body and acts as an antagonist to numerous hormones. For example, this hormone inhibits the formation of the growth hormone somatotropin in the pituitary gland. It can also reduce the secretion of gastric juice or pancreatic secretion. Other hormones whose formation is regulated by somatostatin are: Insulin, cholecystokinin, motilin, or TSH (thyroid-stimulating hormone).
Production, formation, and manufacture
Somatostatin is formed in the human body at several sites. The primary site of formation is the hypothalamus. However, the peptide hormone is also formed endocrine in pancreatic D cells, at the gastric and intestinal walls, and in nerve endings. The nervous and hormonal structure of humans is significantly regulated by this type of hormone. Through its binding to GPCRs (G protein-coupled receptors), it acts on the surface of very different cell types. It retards the motility of the gastrointestinal tract, inhibits the secretion of enzymes in the pancreas, and decreases gastric juice production. Somatostatin also leads to a decrease in pressure in the portal circulation. Two active types of somatostatin hormone are known in the body: Somatostatin-14 and Somatostatin-28. Both are derived from a common propeptide.
Function, action, and properties
Somatostatin is responsible for paracrine secretion in the pancreas. It inhibits the secretion of glucagon, insulin but also STH, cholecystokinin, and gastrin. Because of its effects, somatostatin is used in the following indications: Bleeding from esophageal and cardiac varices, ulcer-related bleeding in the mucosa of the stomach (ulcer bleeding), and acromegaly. In this benign tumor of the pituitary gland, too much growth hormone is produced. Somatostatin counteracts this. In addition, this hormone is used medically in cases of carcinoid symptoms or fistula therapies in the gastrointestinal tract. Since somatostatin has a short half-life of only a few minutes, it is administered in the form of a continuous infusion. The synthetic analogues to endogenous somatostatin are octreotide and lanreotide. These substances, approved as drugs, are used for neuroendocrine tumors. Octreotide, the main component of the drug Sandostatin, is also administered subcutaneously or in capsule form because of its longer half-life.
Diseases, ailments, and disorders
A disturbance in somatostatin levels upsets the body’s entire hormonal balance. Hormone-blocking somatostatin controls the release of growth hormones. Disturbances in this hormonal interplay cause growth abnormalities. If a person produces too little of this peptide hormone, stomach function is also negatively affected. The muscles no longer function properly and the production of pepsinogen becomes imbalanced. Acidosis of the stomach occurs. If this situation becomes chronic, secondary diseases such as esophagitis (reflux esophagitis), bleeding, ulcers or even narrowing of the esophagus are possible. Since somatostatin also regulates the production of glucagon, a malfunction of this hormone leads to blood glucose levels that are too high or too low. Too low a blood glucose level (hypoglycemia) causes unconsciousness, paralysis or cardiac arrest in the worst cases. Glucagon inhibits the breakdown of glucose and stimulates the production of glucose in the liver. Both functions depend on balanced somatostatin secretion. Similarly important, somatostatin behaves in the regulation of insulin production in the human body. The insulin produced in the pancreas is responsible for lowering blood glucose levels.Insulin insufficiency, which can result from increased inhibitory activity of somatostatin, leads to a malfunction in the transport of glucose from the blood plasma to the cells of the adipose tissue, liver or muscles. Various forms of diabetes and organ weaknesses are the most extreme consequences of this insufficiency. Another task of somatostatin is the regulation of the other peptide hormone motilin, which is responsible for gastric distension as well as for the bile and pH drop in the duodenum. A faulty balance between the two hormones causes gastrointestinal disorders. According to recent studies, a serious effect of somatostatin underproduction is also Alzheimer’s dementia. The influence of somatostatin on cognitive learning processes has been demonstrated in animals for some time. Now research results suggest that this finding also applies to humans. One of the most significant neurochemical deficits in Alzheimer’s patients is somatostatin concentration. Defective production of these hormones has also been found in people suffering from depression.
