Growth hormone (growth hormone, somatotropin) in the blood

Growth hormone (growth hormone, somatotropin) is a peptide isolated from the anterior pituitary gland and consists of 191 amino acids. The daily production of growth hormone is approximately 500 μg. The growth hormone stimulates protein synthesis, the processes of cell mitosis and enhances lipolysis. The half-life of the growth hormone in adults is 25 minutes. Inactivation of the hormone in the blood is carried out by hydrolysis. In comparison with other hormones, growth hormone is present in the pituitary gland in the largest amount (5-15 mg / g tissue). The main function of growth hormone is stimulation of body growth. Growth hormone promotes protein synthesis and, interacting with insulin, stimulates the entry of amino acids into cells. It also affects the absorption and oxidation of glucose by fatty tissue, muscles and liver. Growth hormone increases the sensitivity of adipocytes to the lipolytic action of catecholamines and reduces their sensitivity to the lipogenic action of insulin. These effects lead to the release of fatty acids and glycerin from adipose tissue into the blood, followed by their metabolism in the liver. The growth hormone reduces the esterification of fatty acids, thereby reducing the synthesis of TG. Current data suggest that growth hormone can reduce glucose intake by fat tissue and muscles by post-receptor inhibition of insulin action. Growth hormone increases the transport of amino acids to the muscle, creating a supply of substrate for protein synthesis. Through a separate mechanism, growth hormone increases the synthesis of DNA and RNA.

Growth hormone stimulates cell growth either directly or indirectly through IGF I and II. The main biological effects of growth hormone are provided by IGFR I.

The secretion of growth hormone normally occurs unevenly. For most of the day, its concentration in the blood of healthy people is very low. For a day there are 5-9 discrete hormone releases. The low initial level of secretion and the pulsating nature of the emissions make it difficult to evaluate the results of determining the concentration of growth hormone in the blood. In such cases, special provocative tests are used.

[1], [2], [3], [4], [5]

The concentration of growth hormone in the blood serum

Age	STG, ng / ml
Blood from the umbilical cord	8-40
Newborns	10-40
Children	1-10
Adults:
Men's	0-4.0
Women	0-18.0
Older than 60 years:
Men's	1-9.0
Women	1-16

Regulation of the secretion of growth hormone

The regulation of growth hormone secretion is mainly carried out by two peptides of the hypothalamus: STRH, which stimulates the formation of growth hormone, and somatostatin, which has the opposite effect. In the regulation of the secretion of growth hormone, IGFR also participates. An increase in the concentration in the blood of IGFR I suppresses the transcription of the growth hormone genes in the pituitary gland somatotrophs by the negative feedback principle.

The main disorders of the somatotropic function of the pituitary gland are represented by excessive or insufficient production of growth hormone. Gigantism and acromegaly are neuroendocrine diseases caused by chronic hyperproduction of growth hormone by somatotrophs of the anterior lobe of the pituitary gland. Excessive production of growth hormone in the period of osteogenesis before the closure of the epiphyses leads to gigantism. After the closure of the epiphyses, hypersecretion of growth hormone causes acromegaly. Pituitary gigantism is rarely observed, it occurs at a young age. Acromegaly occurs mainly at the age of 30-50 years (the average frequency is 40-70 cases per 1 million population).

The development of hypophyseal nanism (dwarfism) in the vast majority of cases is associated with a lack of somatotropic function of the anterior lobe of the pituitary gland, until its complete loss. The disruption of the production of growth hormone by the pituitary gland is most often (approximately 70% of cases) due to the primary damage to the hypothalamus. Congenital aplasia and hypoplasia of the pituitary gland are very rarely detected. Any destructive changes in the hypothalamic-pituitary region can lead to a halt in growth. Most often, they are caused by craniopharyngiomas, CNS germinomas and other tumors of the hypothalamic region, tuberculosis, sarcoidosis, toxoplasmosis, and aneurysms of cerebral vessels.

Known forms of nanism, mostly hereditary, in which the formation and secretion of growth hormone is not violated. In particular, children with Laron's syndrome have all the signs of hypopituitarism, but the concentration of growth hormone in the blood is increased against the background of a decreased content of IGFR I. The main defect is caused by the inability of the growth hormone to stimulate the production of IGFR I.

Many patients with hypopituitarism fail to detect obvious structural damage to the hypothalamus or pituitary gland; in such cases the pathology is more often caused by functional defects of the hypothalamus. Insufficiency of STH can be both isolated and combined with insufficiency of other pituitary hormones.

The daily rhythm of growth hormone secretion with peaks of its concentration above 6 ng / ml 1-3 hours after falling asleep irrespective of the time of day is formed to 3 months after birth. The average daily concentration of growth hormone increases during puberty, decreases after 60 years; at the same time, diurnal rhythms disappear. Sexual differences in the secretion of growth hormone are not revealed.