Somatostatin - Hormone

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Somatostatin is an important hormone in our body. It plays important functions in different organs of our body, especially in the central nervous system. It is secreted mainly by the pancreas into the bloodstream. Somatostatin deficiency is linked with several neurological and developmental disorders. To treat somatostatin deficiency, several somatostatin analogues like Octreotide are used. Let us look at some of the details associated with Somatostatin.

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Somatostatin Source

The pancreas is the major source of Somatostatin. The source of Somatostatin in the pancreas is the delta cells in the islets of Langerhans. These somatostatin delta cells secrete Somatostatin upon receiving the signal from the pituitary glands. The Somatostatin then functions to prevent the secretion of insulin and glucagon from the adjacent cells. As a result, Somatostatin and insulin display an antagonistic correlation.

In the brain, Somatostatin is secreted by the neuroendocrine neurons located in the hypothalamus. The hormone is secreted and transferred to the hypothalamohypophysial system by the axons of the neurons. The hormone is transported to the anterior pituitary system from this system where it prevents the somatotropin cells from secreting growth hormones. It acts as a feedback mechanism to prevent excess production of growth hormones.

Somatostatin is also secreted by other neurons mainly located in the arcuate nucleus, brainstem nucleus, and hippocampus.

Somatostatin Mechanism of Action

In the pituitary, Somatostatin, glucagon, and insulin work in tandem to regulate the flow of nutrients and sugar from and into the circulatory system. Such a regulation mainly depends on the relative concentration of each of these hormones. In this regulation, the rate of utilization, absorption, and storage of amino acids, sugar, and fatty acids is controlled.   

To have tight control over the regulation of nutrient flow in the circulatory system, the anatomical location and proximity of these hormones’ sources play an important role. The insulin, glucagon, and somatostatin sources are beta, alpha, and delta cells, respectively, in the pancreas. Glucagon and somatostatin work in a paracrine manner, controlling each other’s secretion and together controlling the secretion of insulin.

Somatostatin also plays an important role in regulating the secretion of other gastrointestinal hormones. It inhibits the secretion of gastrin, cholecystokinin, secretin, and vasoactive intestinal polypeptide. All these hormones are important in different gastrointestinal functions- excess of somatostatin secretion and activity inhibit such functions. Some of these functions include secretion of stomach acids, pancreatic digestive enzymes, and nutrient absorption by the intestines.

Somatostatin Deficiency - Related Diseases

Somatostatin deficiency is related to some diseases to date. For example, Alzheimer’s patients demonstrated lower levels of the hormone in the brain. However, it is still unclear the precise role of Somatostatin in the development of the disease.

The late 1970s experienced the development of somatostatinoma. Somatostatinomas are tumors that produce an excess of Somatostatin. After its discovery, several scientists have characterized such tumors. These tumors show a tendency to develop in the pancreas or the intestine, mainly in the jejunum and duodenum. Excess somatostatin secretion results in pain, persistent diarrhea, abdominal cramps, weight loss, high blood glucose levels, and the skin might show episodic flushing. 

Octreotide - An Essential Somatostatin Analog

To counteract the effect of deficiency of Somatostatin, Octreotide is majorly used. This chemical is injected intravenously or subcutaneously. It acts immediately and comes in various forms. The injections that produce octreotide action for short periods are used multiple times a day, while the long-acting ones are used once every 28 days. Both injections are used to treat different disorders.

The Octreotide mechanism of action is similar to that of Somatostatin and is therefore used as a medicinal alternative in the hormone’s deficiency. It inhibits pituitary growth hormone and thyrotropin secretion. Octreotide also inhibits the secretion of glucagon, insulin, and vasoactive intestinal polypeptide. Like Somatostatin, it reduces gastric acid secretion, splanchnic blood flow, the exocrine function of the pancreas, GI motility, and even controls absorption of nutrients, water, and electrolytes from the GI tract.

Scientists have widely studied the Octreotide mechanism, and its application has been directed for several diseases. One such early application of Octreotide is for variceal bleeding. It has been used as a treatment for somatostatin deficiency. Doctors also prescribe Octreotide to treat acromegaly, diarrhea, flushing, VIP-omas, and as a part of surgery and radiation.

FAQ (Frequently Asked Questions)

Q.1 What is the Source of Somatostatin?

Ans: The pancreas is the major source of Somatostatin in the body. Delta cells of the islets of Langerhans are the source of Somatostatin, and the precise anatomical location of these delta cells in relation to the surrounding alpha and beta cells is important for the function of Somatostatin. The alpha and beta cells of the islets of Langerhans are glucagon and insulin sources, respectively. Somatostatin controls the secretion of both these hormones.

Somatostatin is also secreted by the neuroendocrine neurons present in the hypothalamus region of the brain. These neurons transfer the hormone to the hypothalamo hypophyseal axis of the brain, from where it is transferred to the anterior pituitary gland. In this region, Somatostatin inhibits the secretion of the growth hormones from the anterior pituitary.

Q.2 What is the Mode of Action of the Somatostatin?

Ans: Somatostatin is an important hormone of our body that controls the rate of absorption, utilization, and storage of the nutrients, sugar, amino acids, fatty acids, and water from the gastrointestinal tract. It works in conjunction with insulin and glucagon, produced from the pancreas. Somatostatin works in a paracrine manner with glucagon, and both of them control the secretion of insulin from the beta cells in the islets of Langerhans.

Somatostatin prevents insulin secretion from the beta cells. It mainly functions as a checkpoint to control excess production and secretion of insulin and glucagon. Such tight control is necessary to control the absorption of nutrients in the circulatory system. It performs similar functions in the brain, where it controls the secretion of growth hormones from the anterior pituitary gland.

It also controls the secretion of other gastrointestinal hormones like secretin, gastrin, vasoactive intestinal polypeptide, and pancreatic digestive enzymes. It also controls the production of acids in the stomach.