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Steroid hormones. Main pathways of peripheral metabolism

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One of the necessary subsystems in the organization of endocrine functions is the peripheral metabolism of hormones. The most important role in the peripheral transformations of hormones is played by catabolic processes. Hormone catabolism is a set of processes of enzymatic degradation of the original chemical structure of secreted hormonal compounds.

According to the basic physiological essence, catabolic processes, as already noted, are primarily a way of irreversible inactivation of hormones and ensuring hormonal balance, balancing the production of hormones and preparing cells to receive a new portion of hormonal information. Chemical degradation of hormones, carried out using special enzyme systems, occurs in various tissues, but primarily in the splanchnic system and kidneys. These organs determine the inactivation of hormones and prepare them for excretion from the body.

At the same time, the significance of metabolic processes in the periphery is not limited to the irreversible inactivation of hormones. In catabolizing organs and, most importantly, in reacting organs, metabolic processes can occur, leading to activation, reactivation, interconversion of hormones and the emergence of new hormonal activity (Figure 44).

Examples of interconversions of hormones of different types are the conversion of androgens into estrogens in the hypothalamus and in other parts of the brain, as well as in adipose tissue, and the transition of 17-hydroxycorticosteroids into androgens. Finally, the processes of enzymatic transformation of the hormone in the periphery into compounds with a new type of hormonal activity include the formation of enkephalin, endorphins and memory peptides from β-lipotropin. All of these metabolic reactions in responding tissues obviously play an essential role in the local regulation and self-regulation of hormone effectiveness.

Under conditions of physiological rest, metabolic processes in the periphery are in a state of equilibrium with the processes of hormonal production. The pathways and rates of hormone transformations are studied by biochemical methods in vivo and in vitro, generally accepted for any bioorganic compounds.

In this case, 3H-labeled hormones are used. 14C and 125I. Radioactive substances are introduced in physiological concentrations into the body in in vivo experiments or into a medium with incubated pieces, sections, tissue homogenates and subcellular fractions in in vitro experiments. At certain time intervals after the injection of the hormone or the start of incubation of the tissues under study with it, labeled hormonal metabolites from biological material are extracted, purified using various chromatographic procedures, then identified and quantified. In in vivo experiments, the products of hormone transformation are usually determined in excreta.

The half-life of hormones (T1/2) and the metabolic clearance rate (MCR) are often used as integral indicators of the intensity of metabolic processes in vivo.

The half-life of hormones is the time during which the concentration of a portion of a radioactive hormone introduced into the blood is irreversibly halved. In table 12 shows the values of various hormones.

Table 12. Half-life of some hormones in a healthy person (generalized average data)

The metabolism of steroid hormones occurs mainly without cleavage of the steroid skeleton and is reduced mainly to reactions of reduction of the double bond in the A ring (in the main families of hormones, except estrogens); oxidation - restoration of some oxygen functions; hydroxylation of carbon atoms. It is carried out quite intensively not only in the system of catabolizing organs (liver, intestines, kidneys), but also in the brain, muscles, skin and other tissues, excluding the thymic-lymphoid tissue.

All steroid hormones containing a D4-3-keto group in ring A (corticosteroids, progestins, secreted androgens) have a common transformation pathway, consisting of two sequential stages (Dorfman, 1960):

This is how 5a- and 5b-dihydroforms of corticosteroids (dihydrocortisols, dihydrocorticosterones, dihydroaldosterones), progestins (dihydroprogesterones) and testosterone (dihydrotestosterones) are formed. In this case, both 5a- and 5b-reduction of corticosteroids apparently leads to almost complete inactivation of hormones. In the case of progestins, inactivation of the original hormonal compound most often results only in a 5/5 reduction; 5a-dihydroprogesterone (5a-DPr) can have pronounced progestin activity. In the case of androgens, the 5a-reductase reaction leading to the formation of 5a-DT from T causes a significant increase in androgenic activity.

At the same time, 5B reduction of T causes almost complete disappearance of the androgenic and anabolic activity of the hormone in mammals. However, 5b-derivatives of T are probably not . with biologically inert compounds. Losing their androgenic and anabolic activity, they can acquire some new properties. Thus, 5b-DT and some of its metabolites in chicken embryos have the ability to induce hemoglobin synthesis and enhance erythropoiesis (Irving et al., 1975).

The second general stage of transformations of D4-3-ketosteroid hormones, following the 5-reductase reactions, is the hydrogenation of the 3-keto group with the formation of 3- and 3β-hydroxy derivatives of steroid hormones.

These reactions are carried out with the participation of the enzymes 3- and 3β-hydroxysteroid dehydrogenases (oxidoreductases), which, in the presence of NADPH or NADH, reduce 3-keto groups to 3-hydroxy groups. Both enzymes can exist in cells both in soluble form and in a form bound to the membranes of the endoplasmic reticulum. As a result of β-hydroxysteroid dehydrogenase reactions, tetrahydroforms of steroid hormones are formed. Apparently, tetrahydrometabolites of steroids in most cases no longer have direct biological activity and may be the end products of the catabolism of the corresponding hormones.

As a result of the 20-oxide dehydrogenase reaction, 20-dihydro derivatives of C21 steroids are formed, in which the hydroxyl group is oriented either in the 20a- or 20b-position. The substrates for this reaction can be both the original secreted steroids and their tetrahydrometabolites. Moreover, 20a-hydroxy derivatives of the hormones themselves, unlike 20b-derivatives, can have pronounced hormonal activity. At the same time, the 20a-, 20b-dihydroforms of steroids with reduced ring A are biologically inactive. Metabolites of C21-steroids with reduced side chain and reduced A ring constitute a significant portion of the final, excreted metabolites of corticosteroids and progestins.

All of the listed metabolites of steroid hormones are poorly soluble in water and are converted in the liver before excretion into paired compounds (conjugates) - esters with sulfuric, glucuronic and some other acids. The synthesis of ethers with glucuronic acid (glucuronides) and esters with sulfuric acid (sulfates) is the common final step in the catabolism of most steroid hormones, immediately preceding excretory processes.

Esterification of steroids increases their solubility in water and increases the threshold for reabsorption in the convoluted tubules of the kidneys and intestinal mucosa. In addition, in some cases it additionally inhibits the biological activity of the compounds. The stage of formation of paired compounds is nonspecific for steroid hormones.

The formation of an ester bond with metabolites of steroid hormones is a complex enzymatic process that occurs primarily at the hydroxyl of the C3 steroid (see above).

In most species studied, with rare exceptions (eg, the guinea pig), approximately 90% of steroid hormone metabolites are excreted in the form of glucuronides and sulfates. In addition to glucuronides and sulfates, phosphates and conjugates with glutathione, N-acetylglucosamine and proteins are found in excreta (Yudaevidr., 1976).

Polar C21 and C19 carboxymetabolites or their corresponding carboforms were also found in urine (Taylor, 1970; Monder and Bradlow, 1977). The carboxy forms of these compounds are called ethienic acids.

Hormones are biologically active substances, different in chemical nature, which are produced by cells of the endocrine glands and specific cells scattered throughout the body in working organs and tissues.

All hormones have several important properties that distinguish them from other biologically active substances:

1. Hormones are produced in the cells of the endocrine glands and secreted into the blood.

2. All hormones are extremely active substances; they are produced in small dosages (0.001-0.01 mol/l), but have a pronounced and rapid biological effect.

3. Hormones specifically affect organs and tissues through receptors. They fit the receptor like a key to a lock, and therefore only affect susceptible cells and tissues.

4. Hormones are distinguished by the fact that they have a certain rhythm of secretion, for example, hormones of the adrenal cortex have a daily rhythm of secretion, and sometimes the rhythm is monthly (sex hormones in women) or the intensity of secretion changes over a longer period of time (seasonal rhythms).

It is worth noting that biologically active substances that are produced by cells scattered throughout the body are often classified as so-called tissue hormones. Their distinctive features are secretion into tissue fluid and a predominantly local effect, while hormones exert their effect remotely.

By their chemical nature, all hormones can be proteins (peptides), derivatives of amino acids or substances of a steroid nature.

Work regulation

The work of the endocrine glands (the intensity of hormone synthesis) is regulated by the central nervous system. At the same time, the activity of all peripheral endocrine glands is also determined by corrective influences from the central structures of the endocrine system.

There are two mechanisms of influence of the nervous system on the endocrine system: neuro-conducting and neuro-endocrine. The first is the direct influence of the nervous system through nerve impulses on the peripheral glands. For example, the intensity of hormone synthesis can change due to a decrease or increase in the tone of the gland’s vessels, i.e. changes in the intensity of its blood supply. The second mechanism is the influence of the nervous system on the hypothalamus, which, through releasing factors (stimulants - liberins, and secretion suppressors - statins), determines the functioning of the pituitary gland. The pituitary gland, in turn, produces tropic hormones that regulate the activity of peripheral glands.

All endocrine glands are connected to central structures through a negative feedback mechanism - an increase in the concentration of hormones in the blood leads to a decrease in the stimulating effect of the nervous system and the central structures of the endocrine system.

Education

Most hormones are synthesized by endocrine glands in active form. Some enter the plasma in the form of inactive substances - prohormones. For example, proinsulin, which becomes active only after the cleavage of a small part of it - the so-called C-peptide.

Selection

Hormone secretion is always an active process that is strictly regulated by nervous and endocrine mechanisms. If necessary, not only the production of the hormone can decrease, but it can also be deposited in the cells of the endocrine glands, for example, due to binding to protein, RNA, and divalent ions.

Transportation

Transport of the hormone is carried out exclusively by blood. Moreover, most of it in the blood is in bound form with proteins (about 90%). It is worth noting that almost all hormones bind to specific proteins, while only 10% of the pool is bound to a nonspecific protein (albumin). Bound hormones are inactive; they become active only after leaving the complex. If the body does not need the hormone, then over time it leaves the complex and is metabolized.

Receptor interactions

The binding of the hormone to the receptor is a critical step in humoral signal transmission. It is the receptor interaction that determines the specific effect of the hormone on target cells. Most of the receptors are glycoproteins that are embedded in the membrane, i.e. are in a specific phospholipid environment.

The interaction between the receptor and the hormone occurs according to the law of mass action according to Michaelis kinetics. During interaction, both positive and negative cooperative effects can occur. In other words, the binding of a hormone to a receptor can improve the binding of all subsequent molecules to it, or greatly hinder it.

The interaction of a hormone and a receptor can lead to various biological effects; they are largely determined by the type of receptor, namely its location. In this regard, the following variants of receptor localization are distinguished:

1. Superficial. When interacting with a hormone, they change their structure (conformation), due to which the permeability of the membrane increases, and certain substances pass into the cell.

2. Transmembrane. The surface part interacts with the hormone, and the opposite part (inside the cell) interacts with the enzyme (adenylate cyclase or gaunyl cyclase) and promotes the production of intracellular mediators (cyclic adenine or gaunine monophosphate). The latter are so-called intracellular messengers; they enhance protein synthesis or its transport, i.e. have a certain biological effect.

3. Cytoplasmic. Found in the cytoplasm in free form. The hormone binds to them, the complex enters the nucleus, where it enhances synthesis

Messenger RNA and thus stimulates the formation of protein on ribosomes.

4. Nuclear. It is a non-histone protein that binds to DNA. The interaction of the hormone and the receptor leads to increased protein synthesis by the cell.

The effect of a hormone depends on many factors, in particular, on its concentration, on the number of receptors, the density of their location, the affinity (affinity) of the hormone and the receptor, as well as the presence of an antagonistic or potentiating effect on the same cells or tissues of other biologically active substances.

Receptor sensitivity is not only academic, but also of great clinical importance, since, for example, insulin receptor resistance underlies the development of type 2 diabetes mellitus, and blocking receptors in hormone-sensitive tumors (in particular, breast) significantly increases the effectiveness of treatment.

Inactivation

Hormones can be metabolized in the endocrine glands themselves, if they are not needed, in the blood, and also in target organs after they have completed their function.

Hormone metabolism can occur in several ways:

1. Molecule splitting (hydrolysis).

2. Changing the structure of the active center due to the addition of additional radicals, for example, methylation or acetylation.

3. Oxidation or reduction.

4. Bonding of a molecule with a glucuronic or sulfuric acid residue to form the corresponding salt.

The destruction of hormones is not only a means of their disposal after they have completed their function, but also an important mechanism for regulating the level of hormones in the blood and their biological effect. It is worth noting that increased catabolism increases the pool of free hormones, thus making them more available to organs and tissues. If the catabolism of hormones remains elevated for a long enough time, then the level of transport proteins decreases, which also increases bioavailability.

Excretion from the body

Hormones can be excreted by all routes without exception, in particular, by the kidneys with urine, the liver through bile, the gastrointestinal tract with digestive juices, the respiratory tract with exhaled vapors, and the skin with sweat. Peptide hormones are hydrolyzed to amino acids, which enter the general pool and can be used again by the body. The preferential method of excretion of a particular hormone is determined by its solubility in water, structure, metabolic characteristics, and so on.

By the amount of hormones or their metabolites in the urine, it is often possible to track the total amount of hormone secretion per day. Therefore, urine is one of the main media for the functional study of the endocrine system; the study of blood plasma is no less important for laboratory diagnostics.

To summarize, it is worth noting that endocrine system is a complex and multicomponent system, all processes in which are closely interconnected, and dysfunction can be associated with pathology at each of the above stages: from the formation of the hormone to its elimination.

Lecture outline

Features of steroid hormones

Skeleton of steroid hormones

Metabolic origin

The place of steroid hormones in cholesterol metabolism

Stereochemistry of steroids

Steroids with regulatory action

Necessary stages of exchange

10. Classifications of steroid hormones

11. Places of education

12. Classes of steroid hormones

13. General scheme of biosynthesis

14. Common metabolic precursor

15. Androgenic steroids

16. Androgenic steroids

17. Anabolic steroids

18. Estrogenic steroids

19. Estrogenic steroids

20. Synthetic estrogens

21. Progestins

22. Mineralocorticoids

23. Glucocorticoids

24. Circadian rhythm of cortisol secretion

25. Regulators of steroid hormone synthesis

26. Steroidogenic enzymes

27. Steroidogenic enzymes

28. Steroidogenic enzymes

29. Synthesis of steroids in the adrenal glands

30. Regulation of steroid synthesis in the adrenal glands

31. Synthesis of sex hormones

32. Regulation of androgen synthesis

33. Regulation of androgen synthesis

34. Androgen antagonists

35. Aromatase in estrogen synthesis

36. Aromatase in estrogen synthesis

37. Aromatase in estrogen synthesis

44. Steroid hormone receptors

45. Steroid hormone receptors

46. Steroid hormone receptors

47. Regulation of steroid hormone function

48. Steroid hormone receptors

49. Steroid hormone receptors

50. 51. Estrogen receptor coactivators

52. Synergism of hormones

53. Inactivation of steroid hormones

54. Diseases associated with steroid metabolism disorders

Levels of organization of regulatory systems.

The role of hormones in the regulation of metabolism.

Hormones of the adrenal medulla, thyroid, parathyroid and pancreas.

For the normal functioning of a multicellular organism, the interaction between individual cells, tissues and organs is necessary. This relationship is carried out by 4 main regulatory systems.

Central and peripheral nervous systems through nerve impulses and neurotransmitters;

The endocrine system through endocrine glands and hormones that are secreted into the blood and affect the metabolism of various target cells;

Paracrine and autocrine systems through various compounds that are secreted into the intercellular space and interact with receptors either of nearby cells or of the same cell (prostaglandins, gastrointestinal hormones, histamine, etc.);

The immune system through specific proteins (cytokines, antibodies).

Metabolic regulation systems. A - endocrine - hormones are secreted by glands into the blood, transported through the bloodstream and bind to receptors of target cells;

B - paracrine - hormones are secreted into the extracellular space and bind to membrane receptors of neighboring cells;

B - autocrine - hormones are secreted into the extracellular space and bind to membrane receptors of the cell secreting the hormone:

Levels of organization of regulatory systems

3 hierarchical levels.

First level- CNS. Nerve cells receive signals coming from the external and internal environment, convert them into the form of a nerve impulse and transmit them through synapses using chemical signals - mediators. Mediators cause metabolic changes in effector cells.

The second level is the endocrine system. Includes the hypothalamus, pituitary gland, peripheral endocrine glands (as well as individual cells) that synthesize hormones and release them into the blood when exposed to an appropriate stimulus.

The third level is intracellular. It consists of changes in metabolism within a cell or a separate metabolic pathway that occurs as a result of:

- changes in enzyme activity by activation or inhibition;

- changes in the amount of enzymes by the mechanism of induction or repression of protein synthesis or changes in the rate of their destruction;

- changes in transport speed substances through cell membranes.

The role of hormones in the regulation of metabolism and functions

Hormones are integrating regulators that connect various regulatory mechanisms and metabolism in different organs. They function as chemical messengers that carry signals originating in various organs and the central nervous system. The cell's response to the action of a hormone is very diverse and is determined both by the chemical structure of the hormone and by the type of cell to which the action of the hormone is directed.

Hormones(Greek hormao- set in motion) are biologically active substances, different in chemical nature, produced by specialized organs and tissues (endocrine glands) that enter directly into the blood and carry out the humoral regulation of metabolism and body functions. All hormones are characterized by high specificity of action.

Hormonoids- substances produced in a number of tissues and cells (not in specialized organs), like hormones, influencing metabolic processes and functions of the body. Hormonoids often exert their effects within the cells in which they are formed, or they spread by diffusion and act near the site of their formation, while some hormones also enter the bloodstream. There are no sharp differences between hormones and hormonoids.

Endocrine system is a functional association of cells, tissues and organs specialized for internal secretion. Their main function is the synthesis and secretion into the internal environment of the body (incretion) of hormone molecules. Thus, the endocrine system carries out hormonal regulation of vital processes. Endocrine function is possessed by: 1) organs or glands of internal secretion, 2) endocrine tissue in an organ whose function is not limited to internal secretion, 3) cells that have, along with endocrine and non-endocrine functions.

Organs, tissues and cells with endocrine function

	Tissue, cells
Endocrine glands
Pituitary gland a) Adenohypophysis	Corticotrophs Gonadotrophs Thyrotrophs Somatotrophs Lactotrophs	Corticotropin Melanotropin Follitropin Lutropin Thyrotropin Somatotropin Prolactin
b) neurohypophysis	Pituicitis	Vasopressin Oxytocin Endorphins
Adrenal glands a) cortex b) medulla	Zona glomerulosa Zona fasciculata Zona reticularis Chromaffin cells	Mineralocorticoids Glucocorticoids Sex steroids Adrenaline (Norepinephrine) Adrenomedullin
Thyroid gland	Follicular thyrocytes K cells	Triiodothyronine Tetraiodothyronine Calcitonin
Parathyroid glands	Chief cells K cells	Parathyrin Calcitonin
	Pineocytes	Melatonin
Organs with endocrine tissue
Pancreas	Islets of Langerhans alpha cells beta cells delta cells	Glucagon Insulin Somatostatin
Gonads a) testes b) ovaries	Leydig cells Sertoli cells Granulosa cells Corpus luteum	Testosterone Esterogens Inhibin Estradiol Estrone Progesterone Progesterone
Organs with endocrine cell function
Gastrointestinal tract	Endocrine and enterochromaffin cells of the stomach and small intestine	Regulatory peptides
Placenta	Syncytiotrophoblast Cytotrophoblast	Human chorionic gonadotropin Prolactin Estriol Progesterone
	Thymocytes	Thymosin, Thymopoietin, Timulin
	JUGA Peritubular cells Tubules	Renin Erythropoietin Calcitriol
	Atrial myocytes	Atriopeptide Somatostatin Angiotensin-II
Blood vessels	Endotheliocytes	Endothelins NO Hyperpolarizing factor Prostaglandins Adhesion regulators

A system of cells capable of transforming amino acids into various hormones and having a common embryonic origin forms the APUD system (about 40 types of cells found in the central nervous system (hypothalamus, cerebellum), endocrine glands (pituitary gland, pineal gland, thyroid gland , pancreatic islets, adrenal glands, ovaries), in the gastrointestinal tract, lungs, kidneys and urinary tract, paraganglia and placenta) APUD is an abbreviation formed from the first letters of the English. words amines amines, precursor predecessor, uptake assimilation, absorption, decarboxylation decarboxylation; synonym diffuse neuroendocrine system. The cells of the APUD system - apudocytes - are capable of synthesizing biogenic amines (catecholamines, serotonin, histamine) and physiologically active peptides; they are located diffusely or in groups among the cells of other organs. The creation of the concept of the APUD system was facilitated by the simultaneous discovery in peptide-producing endocrine cells and neurons of a large number of peptides that play the role of neurotransmitters or are secreted into the bloodstream as neurohormones. It was found that biologically active compounds produced by cells of the APUD system perform endocrine, neurocrine and neuroendocrine functions.

Features of hormones:

- hormones are present in the blood in very low concentrations

(up to 10 -12 praying);

- their effect is realized through intermediaries - messengers;

- hormones change the activity of existing enzymes or enhance the synthesis of enzymes;

- the action of enzymes is controlled by the central nervous system;

- hormones and endocrine glands are connected by a direct and feedback mechanism.

Many hormonesare transferred by blood not independently, but withproteins blood plasma - carriers.Destroyed hormones in the liver, andare displayed products of their destruction by the kidneys.

In target organs (which hormones reach) on the surface of cells there arespecific receptors , which “recognize” their hormone, sometimes these receptors are not on the cell membrane, but on the nucleus inside the cell.

Synthesized hormones are deposited in the corresponding glands in different quantities:

Stock steroid hormones– enough to supply the body for a period of time several hours,

Stock protein-peptide hormones(in the form of prohormones) is enough for

1 day,

Stock catecholamines- on several days,

Stock thyroid hormones- on several weeks.

The secretion of hormones into the blood (by exocytosis or diffusion) occurs unevenly - it is pulsating in nature, or a circadian rhythm is observed. In the blood, protein-peptide hormones and catecholamines are usually in a free state; steroid and thyroid hormones bind to specific carrier proteins. The half-life of hormones in plasma is: catecholamines - seconds, protein-peptide hormones - minutes, steroid hormones - hours, thyroid hormones - several days. Hormones affect target cells by interacting with receptors; their separation from the receptors occurs after tens of seconds or minutes. All hormones are ultimately destroyed, partially in target cells, especially intensively in the liver. Mainly hormone metabolites and unchanged hormones are excreted from the body in very small quantities. The main route of their elimination is through the kidneys with urine.

Physiological effect of the hormone determined by various factors, for example:

hormone concentration(which is determined by the rate of inactivation as a result of the breakdown of hormones, which occurs mainly in the liver, and the rate of excretion of hormones and its metabolites from the body),

affinity for carrier proteins(steroid and thyroid hormones are transported through the bloodstream in combination with proteins),

number and type of receptors on the surface of target cells.

The synthesis and secretion of hormones are stimulated by external and internal signals entering the central nervous system.

These signals travel through neurons to hypothalamus, where they stimulate synthesis of peptidesreleasing hormones(from English, release - release) - liberins and statins.

Liberins stimulate and statins inhibitsynthesis and secretion of hormones of the anterior pituitary gland.

Hormones of the anterior pituitary gland, calledtropic hormones, stimulate the formation and secretion of hormones from peripheral endocrine glands, which enter the general bloodstream and interact with target cells.

Diagram of the relationship between the body's regulatory systems. 1 - synthesis and secretion of hormones is stimulated by external and internal signals; 2 - signals through neurons enter the hypothalamus, where they stimulate the synthesis and secretion of releasing hormones; 3 - releasing hormones stimulate (liberins) or inhibit (statins) the synthesis and secretion of triple hormones of the pituitary gland; 4 - triple hormones stimulate the synthesis and secretion of hormones from the peripheral endocrine glands; 5 - hormones of the endocrine glands enter the bloodstream and interact with target cells; 6 - changes in the concentration of metabolites in target cells through a negative feedback mechanism suppresses the synthesis of hormones of the endocrine glands and hypothalamus; 7 - the synthesis and secretion of triple hormones is suppressed by hormones of the endocrine glands; ⊕ - stimulation of synthesis and secretion of hormones; ⊝ - suppression of the synthesis and secretion of hormones (negative feedback).

Maintaining hormone levels in the body ensures negative feedback mechanism communications. Changes in the concentration of metabolites in target cells by a negative feedback mechanism suppresses hormone synthesis, acting either on the endocrine glands or the hypothalamus. Synthesis and secretiontropic hormonessuppressed by hormones of endocrine peripheral glands. Such feedback loops operate in hormone regulation systems adrenal glands, thyroid gland, gonads.

Not all endocrine glands are regulated in this way:

G hormones of the posterior lobe of the pituitary gland - vasopressin and oxytocin - synthesized in the hypothalamus as precursors and are stored in terminal axon granules of the neurohypophysis;

The secretion of pancreatic hormones (insulin and glucagon) directly depends on the concentration of glucose in the blood.

Low-molecular protein compounds also participate in the regulation of intercellular interactions - cytokines. The influence of cytokines on various cell functions is due to their interaction with membrane receptors. Through the formation of intracellular messengers signals are sent to the core where they take place activation of certain genes and induction of protein synthesis. All cytokines have the following common properties:

synthesized during the body’s immune response, serve as mediators of immune and inflammatory reactions and have mainly autocrine, in some cases paracrine and endocrine activity;

act as growth factors and cell differentiation factors (they cause predominantly slow cellular reactions that require the synthesis of new proteins);

have pleiotropic (multifunctional) activity.