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Adrenergic Drugs PowerPoint Presentation

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Description : Check out this medical presentation on Pharmacology, which is titled "Adrenergic drugs", to know about the adrenergic drugs (Sympathomimetics and Adrenomimetics).

Tags : Pharmacology, Adrenergic drugs, Sympathomimetics, Adrenomimetics

Published on : Jul 18, 2021 | Views : 2599 | Downloads : 17

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ADRENERGIC DRUGS (Sympathomimetics, Adrenomimetics) Assoc. Prof. I. Lambev Medical University of Sofia E-mail: itlambev@mail.bg www.medpharm-sofia.eu
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The sympathetic preganglionic fibers leave the CNS through the thoracic and lumbar spinal nerves. The sympathetic preganglionic neurons (first neurons) project from the intermediolateral column of the spinal gray matter to the paired paravertebral ganglionic chain lying alongside the vertebral column and to unpaired prevertebral ganglia. These ganglia represent sites of synaptic contact between preganglionic axons (1st neurons) and nerve cells (2nd neurons) that emit postgan- glionic axons terminating on cells in various end organs. In addition, there are preganglionic neurons that project either to peripheral ganglia in end organs or to the adrenal medulla.
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(NOR)ADRENERGIC AND DOPAMINERGIC NERVES NE
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Activation of the Sympathetic Nervous System can be considered a means by which the body achieves a state of maximal work capacity as required in fight or flight situations.
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Whereas ACh serves as the chemical transmitter at ganglionic synapses between first and second neurons Norepinephrine (NE, noradrenaline) is the mediator at synapses of the second neuron. Excitation of the neuron leads to activation of a larger aggregate of effector cells, although the action of released NE may be confined to the region of each junction. Excitation of preganglionic neurons innervating the adrenal medulla causes liberation of ACh. This, in turn, elicits a secretion of epinephrine (adrenaline) into the blood, by which it is distributed to body tissues as a hormone.
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Adrenergic (catecholamine) neurotransmitters Adrenergic receptors: α1 α2 β1 β2 β3
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Adrenoceptors fall into two major groups, designated alpha (α1, α2) and beta (β1, β2, β3) within each of which further subtypes can be distinguished pharmacologically. The different adrenoceptors are differentially distributed according to region and tissue. Agonists at adrenoceptors (direct adrenomimetics) mimic the actions of the naturally occurring catecholamines, NA and epinephrine, and are used for various therapeutic effects.
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Within the varicosities, NE is stored in small membrane-enclosed vesicles (granules, 0.05 to 0.2 µm in diameter). In the axoplasm, L-tyrosine is converted via two intermediate steps to dopamine (DA), which is taken up into the vesicles and there converted to NE by DA-beta-hydroxylase. When stimulated electrically, the sympathetic nerve discharges the contents of part of its vesicles, including NE, into the extracellular space. Liberated NE reacts with adrenoceptors located postjunctionally on the membrane of effector cells or prejunctionally on the membrane of varicosities. Activation of presynaptic α2-receptors inhibits NE (regulative negative feedback).
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Presynaptic receptors in adrenergic synapse and their role in the regulatory negative and positive feedback
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Presynaptic regulation of transmitter release from noradrenergic and cholinergic nerve terminal
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The effect of released NE wanes quickly, because approximately 90% is actively transported back into the axoplasm, then into storage vesicles (neuronal re-uptake). Small portions of NE are inactivated by the enzyme catechol-ortho-methyltransferase (COMT, present in the cytoplasm of postjunctional cells, to yield normeta- nephrine), and monoamine oxidase (MAO, present in the mitochondria of nerve cells and postjunctional cells) to yield 3,4-dihydroxymandelic acid).
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The liver is richly endowed with COMT and MAO. It therefore contrib- utes significantly to the degradation of circulating NE and epinephrine. The end product of the combined actions of MAO and COMT is vanillylmandelic acid.
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Antiparkinsonian dopaminergic drugs moclobemide and selegiline block MAO.
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Action on alpha-adrenoceptors Arterioles and veins (α1): contraction and rise in BP Eye (α1): decreased aqueous secretion GIT (α1): contraction of sphincters Bladder trigone (α1): contraction Uterus (α1): contraction Insulin secretion (α2): inhibited Mail sex organs: ejaculation Salivary glands (α1): water secretion Nictitating membrane in cats (α1): contraction
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Noradrenaline (a1) PLC PIP2 IP3 Ca2+ DAG PKC ADP ATP Ex In (+) Gs
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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.
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Action on beta-adrenoceptors Arterioles and veins (β2): dilation and fall in BP Heart (β1): increased heart rate, force, and conduction velocity Lung (β2): bronchodilation Eye (β2): enhanced aqueous secretion GIT (β2): intestinal relaxation Bladder detrusor (β2): relaxation Uterus (β2): relaxation Liver (β2): glycogenolysis Insulin and glucagon secretion (β2): augmented Fat (β3): lipolysis Kidney (β1): renin release Posterior pituitary (β1): ADH secretion
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Adr (b1&b2) Gs AC ATP cAMP PKA Effects Ex In (+)
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b-ad- reno- ceptor 7 sub- units
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Agents which increase cAMP (adrenaline, salbutamol, and other beta-adrenoceptor agonists) inhibit histamine secretion and produce bronchodilation (antiasthmatic effect).
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Autonomic control of pupil (A) and site of action of mydriatics (B) and miotics (C)
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Chemical structure of catecholamines and affinity for α- and β-receptors
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Norepinephrine (noradrenaline): α1, α2, β1 and β3, but no β2 action Epinephrine (adrenaline): α1, α2, β1 and β2, and weak β3 action Isoproterenol (isoprenaline): β1 and β2, but no α action -------------------------------------------------- Clonidine: presynaptic α2 agonist (with antihypertensive action)
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 Direct-acting adrenomimetics α-adrenomimetics (activators of phospholipase C) - antihypotensive drugs: Etilefrinе, Midodrine, NE - local nasal decongestants: Naphazoline, Oxymetazoline, Xylometazoline (0.1% nasal drops) - eye drops in glaucoma: Phenylephrine Cardioselective β1-adrenomimetics: Dobutamine DA-ergic adrenomimetics: Dopamine Selective β2-adrenomimetics: Fenoterol, Hexoprenaline, Salbutamol, Salmeterol, Terbutaline Non-selective β-adrenomimetics: Iso- and Orciprenaline α- and β-adrenomimetics: Adrenaline (antiallergic): amp. 0,1% 1 ml s.c.; Anapen or Epipen (0,3 mg/03 ml i.m.)  Indirect-acting adrenomimetics Antihypotensive drugs Ephedrine, Mephentermine
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http://www.youtube.com/watch?v=ZR5c5VP2rOs I.M. Pre-filled syringes: Anapen® and EpiPen®: I.M.
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Reactive hyperemia due to α-adrenomimetics (naphazoline, oxymetazoline, xylometazoline) e.g., following decongestion of nasal mucosa
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Some important catecholamines Isoproterenol (USAN) = Isoprenaline (INN)
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BP – blood pressure, HR – heart rate
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Dose-response curves of Adr (adrenaline), NA (noradrenaline) and Iso (isoprenaline) on isolated aortic strip and isolated bron- chial smooth muscle illustrating two distinct rank orders of po- tencies respectively for α- and β-adrenergic receptors. Isolated aortic strip Isolated bronchial smooth muscle
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Effect after 3 to 5 min and duration 4–6 h: Salbutamol Fenoterol Effect after 15–20 min and duration 12 h: Salmeterol
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FACTORS THAT EXACERBATE ASTHMA
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The primary site of bronchodilation action of inhaled β2-adrenergic agonists is mainly bronchiolar smooth muscle. Atropinic drugs cause bronchodilation by blocking cholinergic constrictor tone, act primarily in large airways.
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Selective β2-adrenomimetics with tocolytic effect Fenoterol (Partusisten: tab. 5 mg) Hexoprenaline Salbutamol (Salbupart) Terbutaline
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Ephedra equsetina Ephedrine (indirect adreno- mimetic with antihypotensive and antiasthmatic effects ADR: tachy- phyllaxis
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Indirect sympathomimetics with central stimulant activity and abuse potential Amphetamine Cocaine
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Erythroxylum coca L.