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Тopic Signal molecules, mechanisms of action.

Hormones, chemical nature of the determination methods.

Pituitary and thyroid hormones.

Venue: Chair of Biochemistry.

Duration: 180 minutes
Objectives: Consider the general mechanisms of interaction of signaling molecules with different types of cellular receptors depending on the chemical nature of the signaling molecules. Acquaint students with modern methods for the quantitative determination of hormones and other biochemical approaches for assessing the hormonal status of an organism.

3. Specific tasks

3.1 The student must know: The role and mechanisms of action of signaling molecules. The structure and mechanism of action of hormones as representatives of one of the types of signal molecules. Types of cellular receptors and the mechanisms of interaction of hormones with them. Chemical nature and biological role of pituitary and thyroid hormones. Principles for assessing the hormonal status of an organism.

3.2 The student must be able to : Using qualitative reactions, determine the chemical nature of the hormone.

3.3.1 The student must have the skills to deal with information on the role of hormones and other signaling molecules in the development of pathologies, the basics of the principles of assessing the hormonal status of an organism.

4. Motivation - the doctor needs to have in-depth knowledge about the mechanisms of regulation of metabolism at the hormonal level in order to be able to correct it with drugs.

5. Assignment for self-study:

Students should study recommended literature using self-study questions.

Basic Literature

5.1. Revise the lecture material on the topic: “The mechanism of action of signaling molecules”, “Pituitary and thyroid hormones”

5.2 Биохимия (учебник для ВУЗов под ред. чл.- .корр. РАН, проф. Е.С.Северина, М. 2003, С.545-587 М. 2011, С.534-575

5.3. Use the following textbooks for revision: Березов Т.Т., Коровкин Б.Ф. "Биологическая химия" М., Медицина 1998 , С. 248-283, 289-298.

5.3. Revise for the laboratory work using the following guide books: Учебно-методическое пособие к практическим занятиям по биологической химии часть 2, Санкт-Петербург, 2013

Additional literature

5.5 Study the Section in the text book Марри Р, .Греннер Д, .Мейес П, .Родуэлл В. "Биохимия человека" М., Мир.1993 , С. 158-192.

5.6. Элиот И., Элиот Д. Биохимия и молекулярная биология. Из-во НИИ Биомедицинской химии РАМН, М. 2000, С. 138-142, 291-311.

5.7. Лабораторные методы исследования в клинике ( под ред. В.В.Меньшикова) М.:Медицина,1987-365 с.

5.8. В.С.Камышников Справочник по клинико-биохимическим исследованиям и лабораторной диагностике. М. «МЕДпресс-информ», 2004

5.9. Revise for the tests.

6. Questions for self-study

6.1. Description of the concept of "signaling molecules"

6.2. Classification of hormones by chemical nature and place of formation

6.3. The mechanisms of action of hormones. Characterization of cell receptors.

6.4. The mechanism of action of hormones in a direct type of reception.

6.5. The mechanism of action of hormones in a mediated type of reception

6.6. Types of Membrane Receptors

6.7. Types of indirect signal transmission through the membrane (adenylate cyclase, guanylate cyclase, phosphatidylinositol, Ca types of signal transmission to the cell

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6.8. Types of secondary intermediaries

6.9. The receptor represented by tyrosine protein kinases (insulin receptor and receptors of growth factors, growth hormone and prolactin)

6.10. Receptor internalization, biological role of internalization

6.11. Causes of endocrine disorders, characteristics of diseases of individual endocrine glands a) pituitary hormones (mechanism of action of the pituitary hormones, clinic hypo and hyperfunction of pituitary hormones) b) thyroid hormones (mechanism of action of hormones, clinic of hypo and hyperfunction, endemic goiter).

Question card sample – see Tests section for the topic

Principles for assessing the hormonal status of an organism

1. 
   Diagnosis of endocrine pathology by the concentration of metabolites, the exchange of which directly depends on the function of this hormone
   

The advantage of the approach is the availability of biochemical methods.

The disadvantage is the change in the concentration of the studied metabolite, as a rule, is associated with several reasons, and additional, sometimes several studies are required to identify the true cause. However, in clinic the following methods are used:

а) determination of glucose concentration, for the study of the insular apparatus,

b) determining the concentration of Na and K to assess the work of the adrenal glands,

c) determination of the concentration of Ca and the concentration of oxyproline, which is part of the collagen of the connective and bone tissue to evaluate the parathyroid gland

2. 
   Functional Tests (stimulating and inhibitory) are often used to assess endocrine status.
   

For instance, Loading tests

а) Tests with glucose to detect latent forms of diabetes;

b) Loading test with insulin to assess the function of insulin receptors;

c) АСТН stimulation.

Before administration of ACTH and after 60 minutes the content of 11-hydroxy corticosteroids is determined. In healthy people, the content in the plasma increases by 2-3 times, in urine by 5 times against the initial level. With Itsenko-Cushing's syndrome, the increase is more significant. In primary insufficiency of the adrenal cortex (as opposed to secondary), the growth of 11-hydroxycorticosteroids does not occur

3) Diagnosis of endocrine pathology by determining the concentration of hormones by chemical methods

(determination of corticosteroids).

The methods are laborious and complex. Often, the definition is not used of the hormones themselves, but of the products of their transformation in the body, for example, to determine the functional state of the adrenal cortex, the concentration of 17-ketosteroids, which are their metabolic products that are excreted in the urine, is determined. In women, 17-ketosteroids are formed mainly from hormones of the adrenal cortex, in men 2/3 are formed from hormones of the adrenal cortex and 1/3 due to metabolic conversions of androgens. An increase in the content of 17-ketosteroids is observed in Itsenko-Cushing's disease, adrenal carcinoma, a decrease with weakening of the function of the gonads and less with insufficiency of the adrenal cortex. Methods are very laborious, and are not used at present.

4) Radionuclide analysis methods are the most widely used to analyze the concentration of hormones, certain vitamins, and other substances present in the blood in small concentrations. For these purposes, a saturation (saturated) analysis is used - a research method based on the competitive binding of certain substances (ligands) with an analyte of biological origin and its labeled analogue added from the outside. They compete for the ligand. It is obvious that the more natural hormone in the sample, the less the introduced labeled analog binds. As ligands, antibodies, specific transport proteins, and receptor proteins of target organs are used.

The following types of saturation analysis are distinguished - radionuclide analysis:

• 
  radioimmunological analysis (RIA) - based on the immunochemical reaction of an antigen with an antibody in the presence of a radionuclide-labeled compound
  
• 
  immunoradiometric analysis (IRMA) - differs from RIA in that an antibody is used as a labeled reagent
  
• 
  radio enzymatic analysis - to determine the reagent and its labeled derivative (radio indicator), a specific enzyme associated with the immunosorbent (ELISA) is used,
  
• 
  radio-competitive analysis is based on the competitive interaction between the test substance, its labeled analogue and binding component, which uses specific plasma proteins (for example, thyroxin-binding protein)
  
• 
  radioreceptor analysis - a method in which a tissue receptor is used as a specific binding component of the reaction, and a labeled ligand is used as a radio indicator.
  

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Currently, not only radioactive nuclides are used as labels, but also many other substances:

• 
  fluorescent label
  
• 
  enzyme label
  
• 
  free radical label (with subsequent determination of the content of the bound complex using the method of electron paramagnetic resonance)
  
• 
  immunochemiluminescent method of analysis of the ligand complex
  
• 
  analyte.
  

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anterior pituitary hormones

By the chemical structure, all pituitary hormones are peptides. The synthesis of hormones in the anterior pituitary gland is controlled by hypothalamic liberins and statins. Hormones of the anterior pituitary gland, called tropic hormones, stimulate the formation and secretion of hormones of the peripheral endocrine glands, which enter the general bloodstream and, in turn, affect the production of the corresponding tropic hormones of the pituitary gland according to the principle of negative feedback. Such feedback loops act in the regulation system of hormones of the adrenal glands, thyroid gland, and sex glands. Hormones of the posterior pituitary gland (vasopressin and oxytocin) are synthesized in the hypothalamus as precursors and stored in granules of the terminal axons of the neurohypophysis.

Like peptide hormones, pituitary hormones have a membrane type of receptor. Receptors for the guest hormone, prolactin, and insulin-like growth factor have tyrosine kinase activity. The signal transmission to the cell is accompanied by autophosphorylation of the receptor, followed by a cascade of phosphorylation of cytoplasmic proteins and further activation of cytoplasmic enzymes or signal transmission to the nucleus and activation of transcription factors → change in protein and enzyme synthesis → change in metabolic rate.
1. SOMATOTROPIN, GROWTH HORMONE (GH)

Growth hormone receptors are found in many tissues. GH binds to liver cells and promotes the formation of IGF-1 (an insulin-like growth factor), which mediates the action of the hormone on tissues.

Metabolic effects:

1. Growth-stimulating activity a) stimulates lipolysis, b) increases the permeability of membranes for amino acids, c) enhances protein synthesis, d) stimulates gluconeogenesis, e) enhances glucose uptake by cells f) promotes a positive balance of Ca and Mg.

2. Lactogenic activity.

Lack of GH

In childhood, it leads to stunted growth - dwarfism. There are several types of dwarfism (nanism):

a) dwarfism associated with a lack of growth hormone, b) dwarfism of Laron - production of GH is normal, but there are defect of receptors for GH in the liver

c) dwarfism of pygmies - a postreceptor defect in signal transmission

ExcessGH

In childhood, it causes gigantism, in adulthood - acromegaly (overgrowth of bones and cartilage of the face and limbs)
2. Prolactin, Lactogenic Hormone, LTH

In women, it promotes the initiation and maintenance of lactation, has growth-stimulating activity (receptors are found in many tissues)

In men, prolactin increases the sensitivity of Leydig cells to luteinizing hormone, thus maintaining the necessary level of testosterone synthesis.

Excess LTH (for pituitary tumors)

causes a condition like false pregnancy in women: amenorrhea, gynecomastia - overgrowth of the mammary glands, galactorrhea - the expiration of milk.

In men, it causes impotence and gynecomastia.

Lack of LTH causes infertility.
3. Follicle-stimulating hormone, FSH

The target cells in women are follicles, in men ­ Sertoli's cell of the testes.

Stimulates the growth of female and male germ cells. Deficiency causes infertility.
4. LUTEINIZING HORMONE, LH, INTERSTITIAL CELLS STIMULATING HORMONE, ICS

The target cells in men are the Leydig cells of the testes ­ stimulates the synthesis of androgens.

The target cells in women are ovarian follicles ­ stimulates estrogen synthesis and induces ovulation in the middle of the cycle.

Deficiency causes infertility.
5. TYREOTROPIN, TTG

Stimulates the thyroid gland
6. ADRENOCORTICOTROPINE, ACTH

Enhances the synthesis of hormones of the adrenal cortex, therefore, metabolic manifestations are realized through corticosteroid hormones. Enhances adrenal cortex growth.

Excess ACTH causes Itsenko-Cushing's Disease

a) gluconeogenesis increases, as a result - hyperglycemia

b) the decomposition of amino acids increases, causing a negative nitrogen balance

c) increases the content of fatty acids in the blood (lipotropic effect)

d) sodium retention increases blood pressure and swelling

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e) redistribution of fat (deposited on the face and sides)

f) skin pigmentation due to melanocyte-stimulating ACTH activity

ACTH deficiency leads to a decrease in adrenal cortex function.
POSERIOR PITUITARY HORMONES

They are synthesized in the nuclei of the hypothalamus and move along the axons to the posterior pituitary gland.

Oxytocin

causes contraction of the smooth muscles of the uterus and contraction of the myoepithelial cells surrounding the alveoli of the mammary gland - this promotes the movement of milk into the system of the alveolar ducts and contributes to its release.

VASOPRESSIN or ANTI-DIURETIC HORMONE

has 2 types of receptors:V1 - receptors are located in the smooth muscle cells of blood vessels. The response to the interaction of vasopressin with V1 receptors is vascular contraction. V2 - receptors are located in the cells of the renal tubules, the result of the interaction of the hormone with the receptor is an increase in water reabsorption. With a lack of ADH a disease develops - diabetes insipidus, accompanied by a significant increase in the amount of water released.
Tests for the “Signal molecules, mechanisms of action. Hormones, chemical nature of the determination methods. Pituitary and thyroid hormones” Section.

Тest 1

CHOOSE ALL CORRECT ANSWERS:

Secondary intermediaries are:

а) Na b) Са c) diacylglycerol g) CITP d) cAMP cyclic adenosine monophosphate

Тest 2

CHOOSE THE CORRECT ANSWER:

Myxedema is a disease associated with:

а) hyperthyroidism in childhood

b) hyperthyroidism in adults

c) hypofunction of the parathyroid glands in adults

d) hypofunction of the thyroid gland in childhood

e) hypofunction of the thyroid gland in adults

Тest 3

CHOOSE ALL CORRECT ANSWERS:

The direct (intracellular) type of signal transmission to the cell is characteristic of hormones of the:

а) anterior pituitary

b) adrenal cortex

c) the adrenal medulla

d) pancreas

e) sex hormones

Тest 4

CHOOSE THE CORRECT ANSWER:

Basedow's disease is associated with:

а) hyperfunction of the parathyroid glands

b) hypofunction of the parathyroid glands

c) hyperthyroidism

d) thyroid hypofunction

e) lack of iodine in the soil

Тest 5

CHOOSE ALL CORRECT ANSWERS:

The membrane type of signal transmission to the cell is characteristic of:

а) hormones of the anterior pituitary gland

b) hormones of the posterior pituitary gland

c) hormones of the adrenal cortex

d) hormones of the adrenal medulla

e) thyroxine


Тest 6

CHOOSE ALL CORRECT ANSWERS:

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