Insulin-like growth factor: norm and abnormalities

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.

History of the discovery

Back in the late 50-ies of the twentieth century, scientists suggested that between the somatotropin (STG), which is also called growth hormone, and the cells of the body, there is some mediator. This conclusion implied that the STG influenced only the living organism, but when it was introduced into the muscle cells, even if they were in a nutrient medium, no effect was observed.

In the 1970s, somatomedines were discovered, which were the indicated mediators. They were 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 the insulin-like growth factor 2, as well as the 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 bridges. It is a peptide that binds to blood plasma proteins, so-called growth factor carriers. They allow somatomedine to keep its activity much longer. It lasts for several hours, while in free form this period is not more than 30 minutes.

The hormone is similar to proinsulin, for which it got its name. And in the synthesis of somatomedin, insulin plays an enormous role. After all, it helps the liver to get all the necessary amino acids to start the mechanism of creating an IGF.

Synthesis of the hormone

This 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 receptor stimulation. 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. This hormone stimulates the growth of bones, connective tissue and muscles. Also insulin-like growth factor is synthesized independently in many tissues. If necessary, each cell can provide itself with this substance.

The secretion of IGF-1 by the liver is enhanced by the action of estrogens, androgens, 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 its puberty.

Properties

IGF in muscle cells exerts a growth-stimulating and insulin-like activity. It catalyzes the synthesis of protein and slows down the process of its destruction. It also shifts metabolism, promotes accelerated fat burning.

Insulin-like growth factor 1 is associated with the pituitary and hypothalamus. It is its level in the blood that determines the allocation of other hormones. For example, at a low concentration of it, secretion of somatotropin increases. The production of somatotropin-releasing hormone is also increasing. But with a high level of IGF-1, the secretion of these hormones decreases.

Between somatostatin and insulin-like growth factor, a direct relationship has been established. As one of them increases, the concentration of the second increases.

Separately it is worth noting that it is not worth using it as anabolic to athletes. The results of studies have already been published repeatedly, which speak of negative results of experimental intake of drugs that contain insulin-like growth factor (IGF). Their reception can lead to diabetes, impaired vision, impaired cardiac muscle, neuropathy, hormonal failures. In addition, this substance is one of the main catalysts for the growth of cancer tumors.

Features of IGF

It is noticed that insulin-like growth factor 1 is lowered in old age and in childhood, and the highest in adolescents. But researchers have 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 prone to heart and vascular disease. Separately it is worth noting that its amount increases during pregnancy.

Concentration in the blood during the day is approximately the same. Therefore, it is used to assess abnormalities in the production of somatotropin. 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 determine its exact number.

Decreased hormone concentrations

IGF-1 was discovered only in 1978. Since then, many studies have already been carried out, as a result of which a number of regularities were established. So, his deficiency in childhood is the reason for the delay in the growth and physical development of the baby. But it is also dangerous if the insulin-like growth factor is reduced in adults. After all, there is underdevelopment of muscles, a decrease in the density of bone tissues, a change in the structure of fats.

A deficiency of an IGF can be caused by a number of diseases. Among them there are problems with kidneys, liver. Often the cause of a decreased number of IGF is a disease such as hypopituitarism. This is a condition in which the cavity can stop or the production of hormones by the pituitary gland decreases markedly . But also the production of somatomedin decreases with a nutritional deficiency, or, more simply, starvation.

Increase in FMIs

Despite the severe consequences, which causes the lack of IGF-1, do not assume that increasing its number is not so terrible.

So, if insulin-like growth factor 1 is increased, it will lead to acromegaly in adults and gigantism in children. In children, the disease manifests itself as follows. They begin an intensive growth of bones. This as a result becomes not only the cause of enormous growth, but also the growth of limbs to anomalously large sizes.

Acromegaly, which develops in adults, leads to the expansion of the bones of the legs, hands, 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 violated.

The most common reason for the increase in insulin-like growth factor is the pituitary tumor. It can be disposed of with the help of medications, chemotherapy, and it can also be surgically removed. The analysis helps to determine how successful the therapy is, or to check how well the operation was performed. For example, if the tumor was not completely removed, the concentration of the IGF will be increased.

Conducting research

To diagnose changes in the concentration of insulin-like growth factor in modern laboratory centers, the IHL method is used. This is called immunochemiluminescent analysis. It is based on the immune response of antigens. At the stage of isolation of the necessary substance, beacons are attached to it - phosphors that are visible under the ultraviolet. The level of their luminescence is measured by special equipment - luminometer. It determines the concentration of the substance in the blood serum.

Preparation for research

In order to determine the insulin-like growth factor IGF-1, it is necessary to give blood in the morning, always on an empty stomach. It is allowed only to drink ordinary water. The interval between the last meal and taking the material for the examination should be more than eight hours. It is important that the patient is at rest 30 minutes prior to taking the test. Venous blood is taken for examination.

In addition, experts recommend refusing to perform analysis in the period of acute respiratory diseases (viral or bacterial etiology) in order to exclude false results.

Average indicators

When filling in forms in the laboratory, it is important to specify the age correctly. After all, it depends on what an insulin-like growth factor should be . The norm is set for each age category individually. It is also necessary to focus not on the average indicators, but on the data of the laboratory in which you took the tests. For example, in adolescents aged 14-16 years, the hormone level can be from 220 to 996 ng / ml. And in adults over 35 years of age, it should not exceed 284 ng / ml. The older the patient, the lower the limit level of an FMI should be. After 66 years, the norm is set at 75-212 ng / ml, after 80-66-166 ng / ml.

In children, the level of IGF will also depend on age. In newborn babies, who do not yet have and 7 days, 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

Having determined the insulin-like growth factor, a number of diseases can be diagnosed. An increase in its level indicates not only the gigantism in children or acromegaly in adults. This may be a sign of tumors of the stomach and lungs, chronic renal failure. But separately it is worth noting that it can be increased by taking dexamethasone, alpha-adrenostimulants, beta-blockers.

Decreased levels of IGF in children may indicate dwarfism. In adults, the level is often reduced with hypothyroidism, liver cirrhosis, anorexia nervosa, or simply with fasting. Another one of the possible reasons is chronic lack of sleep and taking a number of drugs with high doses of estrogen.