Prostomatostatin is in turn derived from preprosomatostatin. S-28 is usually released from the endocrine glands of the intestines, whereas S-14 is usually released from the D-cells of the pancreas and the stomach. The biological potencies of both types of somatostatin are different. SS-28 can inhibit the growth hormone secretion to a greater extent compared to SS-14, whereas SS-14 can inhibit glucagon to a greater extent. Somatostatin can be considered to be both an endocrine and an exocrine secretion as it has an effect on two different types of target cells (Bowen, 2002 & Ganong, 2005).
The receptors of somatostatin are of 5 types, namely, SST-1, SST-2, SST-3, SST-4 and SST-5. These receptors are specific to a particular tissue and overall belong to the G-protein coupled receptor super-family. Only one of these receptors can differentiate between the various types of somatostatins. One of the main functions of somatostatin is to reduce the release and the activity of the hormones of the pituitary and other glands of the body. Somatostatin reduces the release of thyrotropin and the growth hormone. It also reduces the activity of glucagon, insulin and several other hormones of the GIT.
It expresses it action on several tissues present in the GIT such as the ECL cells, parietal cells and the G-cells. It reduces the secretion of gastric acid. Due to these actions of somatostatin, it can be utilized in the treatment of several disorders in which the release of hormones is excessive. Usually, somatostatin has a very short-life and cannot be utilized therapeutically. However, nowadays, longer acting versions are present (such as octreotide and Lanreotide) that can be utilized in the treatment of several disorders including hypertension and acromeagly (conditions in which hormones are released in excess).
These longer acting versions of somatostatin basically act on the SST-2 and SST-5 receptors causing an inhibitory effect. Somatostatin can also be utilized in the treatment of gastro-intestinal bleeding. The longer acting versions can also be utilized for diagnostic purposes. Radio-dyes labeled with octreotide can be utilized to take X-rays of tumors that release certain hormones (neuroendocrine tumors). Studies conducted in mice have demonstrated that somatostatin helps to promote sexually dimorphic hepatic gene expression.
Studies have also shown that mice deficient in the somatostatin hormone were able to grow and develop apparently normally (Ganong, 2005). The molecular form of the hormone is S-28, whereas S-14 is the species form. Somatostatin helps in reducing the secretion of gastrin, VIP, GIP, motilin and secretin. It also reduces the secretion of the pancreatic exocrine. It is released into the GI lumen, from where it enters into the blood (Ganong, 2005). A number of neoplasms are treated by administering somatostatin (major therapeutic use of somatostatin). As the hormone can inhibit secretion of growth hormone, it is utilized to treat gigantism and acromeagly (Bowen, 2002).
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