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GENERAL PHARMACO- DYNAMICS

GENERAL PHARMACO- DYNAMICS. Assoc. Prof. I. Lambev E-mail: itlambev@mail.bg. 1. PHARMACO- DYNAMICS OF DRUGS - DEFINITION. Pharmacodynamics: (1) How the drugs act on the body? (2) The mechanism of action of drug and its effects. The mechanism of action represents

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GENERAL PHARMACO- DYNAMICS

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  1. GENERAL PHARMACO- DYNAMICS Assoc. Prof. I. Lambev E-mail: itlambev@mail.bg

  2. 1. PHARMACO- DYNAMICS OF DRUGS -DEFINITION

  3. Pharmacodynamics: (1) How the drugs act on the body? (2) The mechanism of action of drug and its effects.

  4. The mechanism of action represents the interaction between drug molecules and biological structures of the organism.

  5. The effect represents the final results from the drug action. The effect can be observed and measured, but not the action.

  6. Hypotensive effect of acetylcholine (ACh) (Effect or action?) ... 1 min 150 Blood pressure {mm Hg} 100 50 ACh 2 mg i.v. ACh 50 mg ACh

  7. 2. SITES OF DRUG ACTION • They can be divided into: • specific and • non-specific

  8. Non-specific action have: • osmotic • diuretics Mannitol • osmotic • laxative drugs Duphalac MgSO4 • antiacids (antacids) NaHCO3

  9. Specific action It is connected with interaction of the drug with specific site(s) on the cell membrane or inside the cell.

  10. 3. MOLECULAR ASPECTS OF SPECIFIC DRUG ACTION How drugs act?

  11. Main specific targets for drug actions are:  DNA  microbial organelles  target macroproteins

  12.  DNA Alkylating agents bind covalently to sites within the DNA such as N7 of guanine and block DNA-replication.

  13.  Microbial organelles Nystatin Doxy- cyclin Rifampicin Peni- cillins

  14.  Target macroproteins • receptors (> 150 types • with many subtypes) • ion channels • enzymes • carrier molecules

  15. P. Ehrilch (1854-1915) “Corpora non agunt nisi fixata” (a drug will not work unless it is bound).

  16. A. Receptorsare the regulatory macroproteins which mediate the action of endogenous and exogenous ligands (chemicals).

  17. Receptors bind to • Endogenous ligands: • - neurotransmitters (mediators) • - hormones • - autacoids (tissue mediators) • - grouth factors • - inhibitory factors, etc. • Exogenous ligands: • - many (but not all) drugs • - some other xenobiotics

  18. The main receptor ligands are • agonists - activate the receptors • antagonists - block the receptors (Full) (Full) Partial Agonist (unfull antagonist)

  19. The interaction between ligand • and receptor involve weaker, • reversible forces, such as: • Ionic bonding • Hydrogen bonding • Hydrophobic bonding • Van der Waals forces.

  20. The numbers of receptors may be altered during chronic drug treatment, with either an increase in receptor numbers (up-regulation – e.g. beta-antagonists) or a decrease (down-regulation – desensitization: e.g. beta-2 agonists).

  21. The numbers of receptors may be altered during chronic drug treatment, with either an increase in receptor numbers (up-regulation) or a decrease (down-regulation). The therapeutic effect of b-blockers develops slowly. This is probably related to adaptive regulation of receptor numbers.

  22. There are pre- and postsynaptic receptors. Presynaptic receptors may inhibit or increase transmitter release (feedback mechanism: +/-)

  23. Presynaptic receptors in adrenergic synapse and their role in the regulatory negative and positive feedback

  24. There are 4 main types of recep- tors, according to their molecu- lar structure and the nature of receptor-effector linkage. The location of type 1, 2 and 3 receptors is on (into) the cell membranes; type 4 - into the cell nucleus.

  25.  Ionotropic receptors (ligand-gated ion channel receptors) • These receptors are involved • mainly in fast synaptic transmission. • They are proteins containing several • transmembrane segments arranged • around a central channel. • Ligand binding and channel opening • occur on a millisecond time-scale.

  26. Ligand-gated ion channel receptors Effector Coupling Time scale Examples ion channel(Ca2+, Na+, K+, C–) direct milliseconds nACh-receptors GABAA-receptors 5-HT3-receptors

  27. N-receptor: 5 subunits

  28. GABAA- receptors

  29. (-) (-) Antiseizure drugs, induced reduction of current through T-type Ca2+channels. Goodman & Gilman's The Pharmacologic Basis of Therapeutics - 11th Ed. (2006)

  30.  G-protein-coupled receptors All comprise 7 membrane-spanning segments. One of the intracellular loops is larger than the others and interacts with G-protein.

  31. The G-protein is a membrane protein • comprising 3subunits (, , ). The • alpha-subunit possesses GTP-activity. • When the agonists occupy a receptor, • the alpha-subunit dissociates and • then activates a target (effector): • - enzyme (AC, GC, PLC) • - Ca2+ ion channels

  32. AC (adenylate cyclase) catalyses • formation on the intracellular • messenger (cAMP). • cAMPactivates various protein • kinases (PKA and others) which • control cell function in many • different ways by causing phos- • phorylation of various enzymes, • carriers and other proteins.

  33. b-ad- • reno- • ceptor • 7 sub- • units

  34. Adrenaline (b1&b2) (+) Ex Gs AC In cAMP ATP PKA Effects

  35. PLC (phospholipase C) catalyses the • formation of two intracellular messen- • gers - InsP3 and DAG, from memb- • rane phospholipids. • InsP3 (inositol-triphosphate) increases • free cytosolic calcium by releasing • Ca2+ from the endoplasmic reticulum. • Free calcium initiates contractions, se- • cretion, membrane hyperpolarization • DAG activates protein kinase C (PKC).

  36. Noradrenaline (a1) (+) Ex Gs PLC In PIP2 IP3 DAG ADP Ca2+ PKC ATP

  37. The regulation of intracelullular calcium is connected with ryonidine receptors.

  38. Ryanodine receptors (RyRs) form a classof intracellular calcium channels in muscles and neurons. They regulate the releasing of Ca+in animal cells. There are multiple isoforms ofRyRs: RyR1is expressed in skeletal muscle RyR2:in myocardium (heart muscle) RyR3:in the brain.

  39. Ryanodine RyRsare named after the plant alkaloid ryanodine, to which they show high affinity. Ryanodine is a poisonous alkaloid found in the South American plant Ryania speciosa.

  40. Second messenger Protein- kinase Effector AC cAMP PKA PLC IP3 DAG PKC PKG GC cGMP

  41. G-protein-coupled receptors Effector Coupling Time scale Examples Enzyme (AC, GC, PLC); Ca2+channels G-protein seconds AT1-receptors mACh-receptor Adrenoceptors (a, b) H1 – H5-receptors Opioid receptors (m, k, d)

  42.  Tyrosine-kinase receptors • Incorporate thyrosine kinase • in their intracellular domain. • These receptors are involved • in events controlling • phosphorilation, cell growth • and differentiation.

  43. Kinase-linked receptors Effector Coupling Time scale Examples thyrosine kinase direct minutes (to hours) Insulin receptor ANP receptor growth factors rec.

  44.  Nuclear receptors • They are nuclear proteins, so • ligands must first enter cells. • Receptors have DNA-binding • domain. • Stimulation of these receptors • increase protein synthesis by • the activation of DNA transcription.

  45. Nuclear (steroid/thyroid) receptors Effector Coupling Time scale Examples gene transcription via DNA hours steroid receptors thyroid receptors vitamin D receptors

  46. a) Indirect nuclear receptors: Steroid hormones and Calcitriol

  47. b) Direct nuclear receptors: Thyroid hormones (T3, T4) T3 or T4 penetrate the nucleus Combine with their receptors Alters DNA-RNA mediated protein synthesis

  48. Types of receptor-effector linkage (R = receptor; G = G-protein; E = enzyme)

  49. In Ex LAH+ (local anaesthetics) block Na+ channels. B. Ion channels

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