Somatostatin - Hormone
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.
FAQs on Somatostatin
1. What is Somatostatin and what is its other name?
Somatostatin is a polypeptide hormone that plays a crucial role in regulating various physiological functions, primarily by inhibiting the secretion of other hormones. It is also known as Growth Hormone-Inhibiting Hormone (GHIH), which highlights one of its key functions in the body.
2. Where is somatostatin produced in the human body?
Somatostatin is secreted from two main locations in the body:
Pancreas: The delta cells (δ-cells) of the islets of Langerhans in the pancreas secrete somatostatin. Here, it acts locally to regulate the secretion of insulin and glucagon.
Hypothalamus: Neurosecretory cells in the hypothalamus produce somatostatin, which is then transported to the anterior pituitary gland to inhibit the release of growth hormone.
It is also found in smaller amounts in the gastrointestinal tract.
3. What are the main functions of somatostatin as per the CBSE syllabus?
According to the Class 11 NCERT syllabus, the primary functions of somatostatin are:
Inhibition of Growth Hormone: As GHIH from the hypothalamus, it inhibits the secretion of growth hormone (GH) from the anterior pituitary gland.
Regulation of Pancreatic Hormones: In the pancreas, it inhibits the release of both insulin (from beta cells) and glucagon (from alpha cells), helping to fine-tune blood glucose regulation.
Gastrointestinal Effects: It suppresses the secretion of various gastrointestinal hormones and reduces the rate of nutrient absorption from the intestine.
4. How can a single hormone like somatostatin regulate both body growth and blood sugar levels?
Somatostatin achieves this dual regulation through its production in two different locations, acting on different targets. When secreted from the hypothalamus, it travels to the pituitary gland and functions as an endocrine hormone to inhibit growth hormone, thereby controlling body growth. When secreted from the pancreas, it acts as a paracrine hormone, influencing adjacent alpha and beta cells to inhibit glucagon and insulin release, thus directly participating in the regulation of blood sugar levels.
5. What is the key difference between somatostatin and somatotropin?
The key difference lies in their functions; they have opposite effects related to growth. Somatotropin is another name for Growth Hormone (GH), which stimulates growth, cell reproduction, and regeneration. In contrast, Somatostatin (also called Growth Hormone-Inhibiting Hormone) is an inhibitory hormone that suppresses the release of somatotropin (Growth Hormone) from the pituitary gland. In short, somatotropin promotes growth while somatostatin inhibits it.
6. Why is somatostatin considered a major inhibitory hormone in the endocrine system?
Somatostatin is considered a major inhibitory hormone because its primary role across different systems is to suppress or 'put the brakes on' the secretion of other hormones and substances. It doesn't typically stimulate a process but rather controls and tones down existing ones. For example, it inhibits growth hormone in the pituitary, insulin and glucagon in the pancreas, and several hormones like gastrin and secretin in the digestive tract. This widespread inhibitory action makes it a crucial regulator for maintaining hormonal balance (homeostasis).
7. How does somatostatin affect the process of digestion in the gastrointestinal tract?
In the gastrointestinal (GI) tract, somatostatin acts as a powerful inhibitor to slow down the digestive process. Its main actions include:
Reducing the secretion of stomach acid (gastric acid).
Inhibiting the release of GI hormones such as gastrin, secretin, and cholecystokinin (CCK).
Slowing down gastric emptying and muscle contractions of the gut.
Decreasing the absorption of nutrients from the small intestine.
This helps prevent rapid nutrient overload in the blood after a meal.
