An insulin-like growth factor is called a hormone similar in its chemical structure to insulin. It regulates the processes of cell differentiation, their development and growth. Also involved in glucose metabolism.
Discovery story
Back in the late 50s of the twentieth century, scientists suggested that between the growth hormone (STH), which is also called growth hormone, and the body's cells, there is some kind of mediator. This conclusion was suggested due to the fact that STH had an effect only on a living organism, but when it was introduced into muscle cells, even if they were in a nutrient medium, no effect was observed.
In the 1970s, somatomedins, which were the indicated intermediaries, were discovered. They have been called insulin-like growth factors. Initially, 3 groups of such substances were isolated: somatomedin A (IGF-3), B (IGF-2), C (IGF-1). But in the 1980s, it was determined that insulin-like growth factor 2, as well as 3, is only an experimental artifact, but in fact it does not exist. Only the presence of IGF-1 was confirmed.
Structure
Insulin-like growth factor 1 (IGF-1) consists of 70 amino acids that form a chain with intramolecular bridge bonds. It is a peptide that binds to plasma proteins, the so-called carriers of growth factor. They allow somatomedin to remain active for much longer. It lasts several hours, while in free form the indicated period is no more than 30 minutes.
The hormone is similar to proinsulin, for which it got its name. And in the synthesis of somatomedine, insulin directly plays a huge role. After all, it helps the liver to obtain all the necessary amino acids to trigger the mechanism of creating IGF.
Hormone synthesis
The specified growth factor is considered an endocrine mediator, providing the action of growth hormone. It is synthesized by hepatocytes of the liver as a reaction to stimulation of receptors. In tissues, almost all the action of growth hormone is provided by IGF-1. From the liver, it enters the bloodstream, and from there, through the mediation of carrier proteins, into tissues and organs. The specified hormone stimulates the growth of bones, connective tissue and muscles. Also, an insulin-like growth factor is synthesized independently in many tissues. If necessary, each cell can independently provide this substance.
The secretion of IGF-1 by the liver increases under the influence of estrogens, androgens, and insulin. But glucocorticoids lower it. This is considered one of the reasons why these substances affect the growth and development of the body and the rate of puberty.
The properties
IGF in muscle cells has a growth-promoting and insulin-like activity. It catalyzes protein synthesis and slows down the process of its destruction. It also shifts the metabolism, promotes accelerated fat burning.
Insulin-like growth factor 1 is associated with the pituitary gland and hypothalamus. It of its level in the blood depends on the release of other hormones. For example, at a low concentration, the secretion of growth hormone increases. The production of growth hormone releasing hormone also increases . But at a high level of IGF-1, the secretion of these hormones decreases.
A direct relationship has been established between somatostatin and an insulin-like growth factor. With an increase in one of them, the concentration of the second also increases.
Separately, it is worth noting that athletes should not use it as an anabolic. Research results have been published many times that report negative results from the experimental use of drugs that contain insulin-like growth factor (IGF). Their use can lead to diabetes, visual impairment, impaired functioning of the heart muscle, neuropathy, hormonal disruptions. In addition, this substance is one of the main catalysts for the growth of cancerous tumors.
IGF Features
It is noted that insulin-like growth factor 1 is reduced in old age and in childhood, and it is highest in adolescents. But the researchers also found that older people who have a level of this hormone closer to the upper limit of the norm for their age group live longer. In addition, they are less susceptible to diseases of the heart and blood vessels. Separately, it is worth noting that its number increases during pregnancy.
The concentration in the blood during the day is approximately the same. Therefore, it is used in order to assess violations in the production of growth hormone. After all, the concentration of growth hormone in the blood changes throughout the day, the maximum level is determined at night. Therefore, it is problematic to precisely determine its amount.
Hormone reduction
IGF-1 was discovered only in 1978. Since then, quite a lot of research has already been carried out, as a result of which a number of patterns were established. So, its deficiency in childhood is the cause of stunting and physical development of the baby. But it is also dangerous if the insulin-like growth factor is reduced in adults. Indeed, at the same time, underdevelopment of muscles, a decrease in bone density, and a change in the structure of fats are noted.
Deficiency of IGF can be caused by a number of diseases. Among them are problems with the kidneys and liver. Often the cause of a reduced amount of IGF is a disease such as hypopituitarism. This is a condition in which the production of hormones by the pituitary gland can cease or decrease markedly . But the production of somatomedin is also reduced with a nutritional deficiency, or, more simply, starvation.
Increased IGF
Despite the grave consequences caused by the lack of IGF-1, one should not assume that an increase in its number is not so scary.
So, if insulin-like growth factor 1 is increased, then this will lead to acromegaly in adults and gigantism in children. In babies, the disease manifests itself as follows. They begin intensive bone growth. As a result, this causes not only huge growth, but also an increase in limbs to anomalously large sizes.
Acromegaly, which develops in adults, leads to the expansion of the bones of the legs, arms, face. Internal organs also suffer. This can lead to death due to cardiomyopathy - a disease in which the heart muscle is affected, its functions are impaired.
The most common cause of an increase in insulin-like growth factor is a pituitary tumor. You can get rid of it with the help of medications, chemotherapy, and it can also be removed surgically. The analysis helps to determine how successful the therapy is, or to check how well the operation was performed. For example, if the tumor has not been completely removed, the concentration of IGF will be increased.
Conducting research
To diagnose changes in the concentration of insulin-like growth factor in modern laboratory centers, the IHLA method is used. So called immunochemiluminescent analysis. It is based on the immune response of antigens. At the stage of separation of the necessary substance, beacons are attached to it - phosphors that are visible under ultraviolet light. The level of their glow is measured on special equipment - a luminometer. It determines the concentration of the released substance in blood serum.
Study preparation
In order to determine the insulin-like growth factor IGF-1, it is necessary to donate blood in the morning, always on an empty stomach. Allowed only to drink ordinary water. The interval between the last meal and the collection of material for the study should be more than eight hours. It is important that the patient is at rest 30 minutes before the test. For research take venous blood.
In addition, experts recommend abandoning the analysis during acute respiratory diseases (viral or bacterial etiology) in order to exclude false results.
Averages
When filling out forms in the laboratory, it is important to correctly indicate the age. After all, it depends on him what the insulin-like growth factor should be . The norm is set for each age category individually. It is also necessary to focus not on average indicators, but on the data of the laboratory in which you passed the tests. So, for example, in adolescents aged 14-16 years, the level of the hormone can be from 220 to 996 ng / ml. And in adults who are more than 35 years old, it should not exceed 284 ng / ml. The older the patient, the lower the limit level of IGF should be. After 66 years, the norm is established in the range of 75-212 ng / ml, after 80 years - 66-166 ng / ml.
In children, the level of IGF will also depend on age. In newborn babies who are not yet 7 days old, it should be from 10 to 26 ng / ml. But after 16 days and up to 1 year, the norm is set at 54-327 ng / ml.
Diagnosis of diseases
By identifying an insulin-like growth factor, a number of diseases can be diagnosed. An increase in its level indicates not only gigantism in children or acromegaly in adults. This may be a sign of tumors of the stomach and lungs, chronic renal failure. But it is worth noting separately that you can increase it by taking dexamethasone, alpha-adrenostimulants, beta-blockers.
A decrease in the level of IGF in children may indicate dwarfism. In adults, the level is often reduced with hypothyroidism, cirrhosis, anorexia nervosa, or simply starvation. Another possible reason is called chronic lack of sleep and taking a number of drugs with high doses of estrogen.