What' s Somatomedin?
Somatomedins are a group of proteins produced predominantly
by the liver when growth hormones act on target tissue. Somatomedins inhibit
the release of growth hormones by acting directly on anterior pituitary and by
stimulating the secretion of somatostatin from the hypothalamus.
Somatomedins have similar biological effects to
somatotropin.
Somatomedins are secreted and activated in response to
growth hormone. Somatomedin levels rise progressively during childhood, peak at
puberty, and then stabilize at lower levels in adulthoodad. Somatomedins influence
calcium, phosphate, carbohydrate, and lipid metabolism and have also been
associated with the growth of certain cancers. Also called insulinlike growth
factor
In addition to their actions that stimulate growth,
somatomedins also stimulate production of somatostatin, which suppresses growth
hormone release. Thus, levels of somatomedins are controlled via negative
feedback through the intermediates of somatostatin and growth hormone.
Somatomedins are produced in many tissues and have autocrine and paracrine
actions in addition to their endocrine action. The liver is thought to be the
predominant source of circulating somatomedins.
Three Forms Somatomedin
1. Somatomedin A, which is another name for insulin-like growth factor 2 (IGF-2)
Somatomedin A or IGF2 Insulin-like growth factor 2 (IGF-2)
is a protein hormone. IGF-2 is influenced by placental lactogen and plays a
role in fetal development. It undergoes glucose-mediated co-secretion with
insulin and acts as physiological amplifier of glucose-mediated insulin
secretion. It exhibits osteogenic properties by increasing osteoblast mitogenic
activity through phosphoactivation of MAPK1 and MAPK3.
2. Somatomedin B
Somatomedin
B is a serum factor of unknown functio, is a small cysteine-rich peptide, derived
proteolytically from the N-terminus
of the cell-substrate adhesion protein vitronectin. Cys-rich somatomedin B-like domains are found in a number of
proteins, including plasma-cell
membrane glycoprotein (which has nucleotide pyrophosphate and alkaline
phosphodiesterase I activities) and placental protein 11 (which appears to
possess amidolytic activity).
3. Somatomedin C
Somatomedin C/ IGF-1 (Insulin -like Growth Factor 1) belongs
to a family of polypeptide hormones, which are structurally close relatives of
insulin. Circulating IGF-1 is synthesised in the liver. Serum level of
somatomedin is regulated by: growth hormone (GH), insulin and nutrition. It is
also produced locally by most tissues, where it acts in auto- and paracrine
manner. IGF-1 takes part in regulating growth after binding to IGF receptor
during embryonic development and after birth. In adults somatomedin plays a
role in the process of regeneration, mainly in the case of connective tissue.
It is also a weak mitogen for most cultured cells and it can act like insulin.
Somatomedin circulates in plasma in complex with a family of binding proteins.
85-95% of total IGF-1 is found in the complex consisting of IGF-1, binding
protein 3 and ALS. This complex is a store of IGF and limits the access of
somatomedin to specific receptors. After binding with IGFBP-1, IGFBP-2 and
IGFBP-6, IGF-1 passes through epithelium and reaches the target cells. The
serum concentration of this protein appears to be inversely related to insulin
level. IGFBP-1 can modulate IGF growth-promoting effect. IGF and its binding
proteins are important in the diagnosis and treatment of some pituitary
diseases, catabolic states such as malnutrition, burns, AIDS, polytrauma and
tumors with hypoglikemia.
Insulin-like growth factors may be involved in the
etiopathogenesis of diabetes and in diabetes complications. Abnormalities in
functioning of GH-IGF-1 axis are regarded as a cause of the growth retardation
in children with poor metabolic control of type 1 diabetes, insulin-resistance,
dawn phenomenon and fat disorders. rhIGF has been used in the treatment of some
diseases bringing positive results.
Sources;
1. https://en.wikipedia.org/wiki/Somatomedin
2. https://www.ncbi.nlm.nih.gov/pubmed/12818085
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