SOMATOMEDINS — biologically active polypeptides of blood serum possessing growth and insulinopodobny action.
For the first time S. were described by W. D. Salmon and Dodey (W. N of Daughaday) in 1957 under the name «sulphurizing factor» — the factor of blood serum which is formed under the influence of somatotropic hormone (see) and stimulating inclusion of sulfate in cartilaginous tissue. The term «somatomedins» offered by Dodey and soavt. in 1972, reflects an orientation of action of S., their communication with somatotropic hormone (STG) and participation as intermediaries in implementation biol. effects of STG.
Carry the somatomedins A and C emitted from blood serum of the person and also the insulinopodobny growth factors of I and II (IRF-1 and IRF-P) which are components of the system of the substances of blood serum of the person having insulinopodobny activity which is not suppressed by anti-insulin antibodies to group C. Besides, carry the substances showing the animation stimulating activity (MCA) to S., edges it is found in the serum-free environment of culture of cells of a liver of rats and consists in ability to stimulate proliferation of fibroblasts of chicken embryos. Each of these factors was found as the carrier of one specific biol in due time. effect, according to the Crimea also received the initial name. During the further researches it became clear that each such factor, in addition to originally revealed activity, in a varying degree has activity of all other members of family C.
Community biol. properties C. it is combined with similarity of their chemical structure. In total S. are one-chained polypeptides about a pier. it is powerful (weighing) 6000 — 8500. IRF-1 is constructed of 70 amino-acid remains (a pier. weight 7649), IRF-P — from 67 amino-acid remains (a pier. weight 7471); on structure of IRF are similar with each other and find a clear homology with pro-insulin (see). The liver of rats of MCA found in culture of cells several polypeptides possess. One of them is allocated in a homogeneous state, its primary structure differs from structure of IRF-II only on five amino-acid remains. The data which are available about primary structure of somatomedin C confirm its close similarity to structure of IRF-1.
Range biol. S.'s activities it is extremely wide. In total S. find the stimulating activity in a growth ratio of a cartilage and a number of processes in this fabric — transport of amino acids in cells, synthesis of DNA, RNA and protein, synthesis of proteoglycans and collagen. In total S. have the insulinopodobny activity which is shown in muscular tissue stimulation of transport of amino acids and glucose in cells and an intensification of formation of a glycogen and synthesis of protein; in fatty tissue stimulation of transport of glucose and its oxidation to carbonic acid, inclusion of glucose in lipids and suppression of a lipolysis. For different S. degree of similarity of their effects to action insulin (see) it is various. Pages have own specific receptors in the most various cells, but show also nek-ry ability to interaction with receptors of insulin. Villages have the mitogenetic activity which is shown in stimulation of synthesis of DNA and cell fission in cellular cultures. Different S. are characterized perek by a restny immunoreactivity on the relation to each other.
Along with somatomedins A and C from blood serum of the person the polypeptide constructed of 44 amino-acid remains also dependent on STG and stimulating proliferation of nek-ry cells in culture was emitted. This polypeptide was called somatomedin B. However, as it has no structural looking alike insulin and insulinopodobny activity and is not active concerning a cartilaginous and bone tissue, it is not included in group of somatomedins.
The most important source of S. circulating in blood are cells of a liver. At the same time it is established that S. are formed also in other cells and fabrics — in fibroblas-ta, cartilaginous tissue, kidneys.
For S.'s definition in blood serum and fabrics use biol. the method based on establishment of inclusion of marked sulfate in cartilaginous tissue, the radio receptor methods based on specific binding of S. by membranes of cells of a placenta or a liver using marked radioisotopes of standards and radio immunological method (see).
In blood C. circulate generally in the form of complexes with specific carrier proteins. The unbound state in blood contains less than 5% of all Pages. S.'s maintenance in blood depends on age. At fruits of the person and newborns the content of immunoreactive somatomedin A in blood is extremely low, at children's age it gradually raises, reaching by 10 years of the sizes characteristic of adults. After short-term increase in the pubertal period concentration of somatomedin A in blood up to 30 years almost does not change, and then shows a tendency to decrease to the sizes observed at newborns. In a similar way during life the content in IRF-1 blood and somatomedin C changes. Assume that growth in the embryonal and early post-natal period is regulated by a special (embryonal) form C. or does not depend on Page at all.
The leading role in maintenance of normal concentration of S. in blood belongs to STG. Between the maintenance of STG and somatomedins in blood serum there is a directly proportional dependence. Other hormones also take part in regulation of somatomedinovy activity of blood serum (see). Under the influence of insulin, thyroid hormones (see. Tiroksin , Triiodothyronine ), prolactin (see) and sex hormones (see) in the pubertal period S.'s activity in blood serum increases, and under the influence of glucocorticoid hormones (see) — decreases. Character of food also affects S.'s activity in blood serum. Many nutrients cause increase in somatomedinovy activity in blood serum, at starvation it goes down. Regulation of education of different S. and its dependence on STG is not identical. Concentration of IRF-II in blood serum by 3 — 5 times exceeds concentration of IRF-1 and in comparison with the last in much smaller degree depends on STG. Concentration of IRF-II does not increase at acromegalias (see) and goes down a little at hypopituitarism (see).
Close connection between STG and somatomedins — alleged intermediaries of rostostimuliruyushchy action of STG — is not absolute. Certainly, S. cannot consider the only factors realizing rostostimuliruyushchy effect of STG, besides, function C. most likely is not limited only to mediation in rostostimuliruyushchy action of STG, and is much more diverse and for different S. can be various.
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Yu. A. Pankov, A. A. Bulatov.