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.