SOMATOSTATIN.pptx

All about Somatostatin

1. SOMATOSTATIN By - Prashant Singh Group- 402

2. Table of Contents What is it? Functions Stimulation Substitutes Increased Somatostatin Levels Decreased Somatostatin Levels

3. What is it? It is a polypeptide hormone produced by neuroendocrine neurons of the ventro-medial nucleus of the hypothalamus neurons and in the delta cells of the islets of Langerhans. It has two active forms produced by the alternative cleavage of a single preproprotein: one is 14 amino acids, and the other is 28 amino acids. It acts as a short peptide chain neurotransmitter in the nervous system.

4. It can also be known as growth hormone-inhibiting hormone (GHIH) or somatotropin release-inhibiting factor (SRIF) or somatotropin release-inhibiting hormone. Across all vertebrates, there have been found to be six different somatostatin genes along with five different somatostatin receptors which allows somatostatin to possess a large range of functions. Humans however, only posses one of those genes, SST.

5. Functions It is secreted by many tissues in the body, principally in the nervous and digestive systems and performs functions specific to the area it is secreted. 1) Hypothalamus - Its function here is always paracrine. It inhibits the pituitary gland’s secretion of growth hormone, thyroid stimulating hormone, prolactin, and adenylate cyclase in parietal cells. 2) Pancreas - inhibits the secretion of pancreatic hormones such as insulin and glucagon.

6. 3) Gastrointestinal tract - reduces stomach acid secretion by acting on parietal cells and by inhibiting the release of other hormones, including gastrin, secretin, histamine and many more. It also reduces intestinal absorption of glucose. Finally, it decreases the rate of gastric emptying, and reduces smooth muscle contractions and blood flow within the intestine.

7. Stimulation The somatostatin neurons in the hypothalamus mediate negative feedback effects of growth hormone on its own release. For example: the somatostatin neurons respond to high circulating concentrations of growth hormone and somatomedins by increasing the release of somatostatin, in turn reducing the rate of secretion of growth hormone.

8. Somatostatin secreted by the pancreas controls many factors related to food intake, such as high blood levels of glucose and amino acids. When released it produces a decrease in blood glucose concentration. Secretion is induced by low pH (high acid amount) in the gastric lumen. When secreted into the gastric lumen it mixes with the gastric juice. Thereafter, it acts on the gastric mucosa to inhibit gastrin secretion.

9. Substitutes Knowing the functions of somatostatin, we can start to use it in medical therapy to control excess hormone secretion disorders such as acromegaly, gigantism, other endocrine conditions, and to also treat some gastrointestinal diseases. This can be done by using either somatostatin or a synthetic substitute. Here are two examples of synthetic substitutes for somatostatin: 1. Octreotide , which is an octapeptide that mimics natural somatostatin pharmacologically, though is a more potent inhibitor of growth hormone, glucagon, and insulin than the natural hormone. It is indicated for symptomatic treatment of carcinoid syndrome and acromegaly.

10. 2. Lanreotide is a medication used in the management of acromegaly and symptoms caused by neuroendocrine tumors, most notably carcinoid syndrome. It is a long-acting analogue of somatostatin, like Octreotide. o Carcinoid syndrome refers to the array of symptoms that occur secondary to carcinoid tumors.

11. Increased Somatostatin Levels The normal somatostatin concentration in plasma is 13.3 (+/- 5.3) pg/ml. Excessive somatostatin levels in the bloodstream may be caused by a rare endocrine tumour that produces somatostatin, called somatostatinoma. Too much somatostatin in the blood results in the extreme reduction in secretion of many endocrine hormones.

12. An example of this is suppression of insulin secretion from the pancreas leading to raised blood glucose levels and eventually diabetes mellitus. As somatostatin inhibits many functions of the gastrointestinal tract, its overproduction may also result in the formation of gallstones, intolerance to fat in the diet and diarrhoea.

13. Decreased Somatostatin Levels Since somatostatin regulates many physiological processes, small amounts of somatostatin production would lead to a variety of problems. The excessive secretion of growth hormone and TSH. This could lead to other problems such as acromegaly, gigantism, other endocrine conditions, and some gastrointestinal diseases. However, there are very few reports of somatostatin deficiency.