Somatostatin is a polypeptide hormone produced in the hypothalamus and pancreas that inhibits the secretion of several other hormones. It acts as a neurotransmitter in the nervous system and regulates processes in the gastrointestinal tract and pancreas. Synthetic substitutes like octreotide and lanreotide are used to treat excess hormone secretion and gastrointestinal diseases by mimicking somatostatin. Increased somatostatin levels can result from rare tumors and cause issues like diabetes and gallstones by over-suppressing hormone secretion. Decreased levels can lead to problems from excessive growth hormone and thyroid stimulating hormone secretion.

1. Somatostatin
Completed By : Khaled Alkhodari
Sadeq Elmezaini
Supervised By: Dr. Omar Ferwanah

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. What is it? - Cont’d
 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. Functions Cont’d
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. Stimulation – Cont’d
 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.
Substitutes Cont’d

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. Increased Somatostatin Levels – Cont’d
 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.

14. Review
 What is it?
 7 points
 Functions
 14 points
 Stimulation
 5 points
 Substitutes
 5 points
 Increased Somatostatin Levels
 6 points
 Decreased Somatostatin Levels
 3 points