Adrenergic receptor and mechanism of action by yehia matter

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Information about Adrenergic receptor and mechanism of action by yehia matter
Health & Medicine

Published on February 20, 2014

Author: yehiamatter



Adrenergic receptor and mechanism of action by yehia matter

Adrenergic receptor and mechanism of action

AUTONOMIC NERVOUS SYSTEM • Central Nervous System (CNS) - Brain and spinal cord • Peripheral Nervous System (PNS) - Located outside the brain & spinal cord * Autonomic Nervous System (ANS) & the somatic • The PNS receives stimuli from the CNS & initiates responses to the stimuli after it’s interpreted by the brain

AUTONOMIC NERVOUS SYSTEM • ANS acts on smooth muscles & glands • - Controls & regulation of the heart, respiratory. system, GI tract, bladder, eyes & glands - Involuntary - person has little or no control Somatic - voluntary - person has control (skeletal muscle)

ANS • ANS has 2 sets of neurons: 1. Afferent (sensory) - sends impulses to the CNS for interpretation 2. Efferent - receives impulses (info.) from the brain & transmits from the spinal cord to the effector organ cells - 2 branches - sympathetic & parasympathetic nervous system


ANS - SYMPATHETIC NERVOUS SYSTEM (ADRENERGIC) • Sympathetic Nervous System (adrenergic) Norepinephrine = neurotransmitter - Drugs that mimic = adrenergic drugs, sympathomimetics, or adrenomemetics * Adrenergic agonists - Drugs initiate a response - Drugs that block = adrenergic blockers, sympatholytics or adrenolytics * Adrenergic antagonists - prevent a response

ANS • 4 types of adrenergic receptor organ cells: 1. Alpha-1 = vasoconstriction of blood vessels inc. blood return to heart, inc. circulation, inc. BP 2. Alpha-2 = inhibits release of norepinephrine dec. in vasoconstriction, dec. BP 3. Beta-1 = inc. in heart rate & force on contraction 4. Beta-2 = relaxation of smooth muscle in bronchi, uterus, peripheral blood vessels Dopaminergic = dilate vessels, inc. in blood flow - only dopamine activates this receptor

ANS - PARASYMPATHETIC NERVOUS SYSTEM (CHOLINERGIC) • Parasympathetic or Cholinergic Nervous System Acetylcholine = neurotransmitter - Drugs that mimic = cholinergic drugs, parasympathomimetics Cholinergic agonists - initiates a response - Drugs that block = anticholinergic, parasympatholytics Cholinergic antagonists - prevents a response

ANS • Sympathomimetic pathway Norepinephrine From adrenergic fiber Inc. heart rate Pupil dilation Adrenergic (sympathomimetic) agents Fight or Flight • Parasymathomimetic pathway Acetylcholine From cholinergic fibers Dec. heart rate pupil constriction Cholinergic (parasympathomimetic agents)

ADRENERGICS AND ADRENERGIC BLOCKERS • Drugs that Stimulate the sympathetic Nervous System (adrenergics, adrenergic agonists, sypathomimetics, or adrenomimetics) • Mimic the sympathetic neruotransmitters norepinephrine and epinephrine • Act on one or more adrenergic receptor sites located on the cells of smooth muscles - heart, bronchioles, GI tract, bladder, eye • 4 main receptors (alpha-1, alpha-2, beta-1, beta-2)


MECHANISM OF ADRENERGIC RECEPTORS There are two main groups of adrenergic receptors, α and β, with several subtypes. •α receptors have the subtypes α1 (a Gq coupled receptor) and α2 (a Gi coupled receptor). Phenylephrine is a selective agonist of the α receptor. •β receptors have the subtypes β1, β2 and β3. All three are linked to Gs proteins (although β2 also couples to Gi),[2] which in turn are linked to adenylate cyclase. Agonist binding thus causes a rise in the intracellular concentration of the second messenger cAMP. Downstream effectors of cAMP include cAMP-dependent protein kinase (PKA), which mediates some of the intracellular events following hormone binding. Isoprenaline is a non-selective agonist.

Adrenaline or noradrenaline are receptor ligands to either α 1, α 2 or β adrenergic receptors. α 1 couples to Gq, which results in increased intracellular Ca2+ and subsequent smooth muscle contraction. α 2, on the other hand, couples to Gi, which causes a decrease of cAMP activity and a resulting smooth muscle relaxation. β receptors couple to Gs, and increases intracellular cAMP activity, resulting in e.g. heart muscle contraction, smooth muscle relaxation and glycogenolysis .

MOLECULAR MECHANICS OF ADRENRGIC RECPTOR Beta adrenergic receptor kinase (βARK) is a serine/threonine intracellular kinase. It is activated by PKA and its target is the beta adrenergic receptor. βARK Activation : 1.Upon stimulation of the Beta adrenergic receptor by epinephrine, Gs will be activated. 2.Gs alpha will then stimulate adenyl cyclase to make cAMP. 3.cAMP will then activate cAMP-dependent kinase (PKA), which, among other proteins that it acts on, will phosphorylate serine and threonine residues on β AR K. 4.β ARK, itself a serine/ threonine kinase, will then phosphorylate serine and threonine resides on the β -adrenergic receptor itself. 5.This will facilitate Beta-arrestin's binding to the receptor. Additional stimulation by epinephrine will now be unable to activate Gs due to arrestin. Therefore, β AR is a negative feedback enzyme that will prevent overstimulation of the β K adrenergic receptor.

SYMPATHOMIMETICS/ ADRENOMIMETICS • Stimulate adrenergic receptors: 3 categories 1. Direct-acting = directly stimulates receptors (epinephrine or norepinephrine) 2. Indirect-acting = stimulates release of norep. from terminal nerve endings (amphetamine) 3. Mixed-acting (indirect & direct) = stimulates receptor sites & release of norep. from nerve endings (Ephedrine)

SYMPATHOMIMETIC AGENTS/ ADRENERGICS • Action - Many of the adrenergic drugs stimulate more than one of the adrenergic receptor sites (alpha & Beta) • Response = Inc. BP, pupil dilation, inc. HR, & bronchodilation • Use = Cardiac stimulation, bronchodilator, decongestant • Side effects = Hyperness in body

SYMPATHOMIMETICS/ADRENER GICS • Albuterol - Beta-2 agonist (bronchodilation) Use - bronchospasm, asthma, bronchitis SE - nervousness, restlessness CI - severe cardiac disease, HTN • Epinephrine - stimulates alpha & beta Use - allergic reaction, cardiac arrest SE - nervousness, agitation CI - cardiac dysrhythmias

ADRENERGIC AGENTS • Dopamine - alpha-1 & beta-1 stimulation Use - Hypotension, shock, inc. cardiac output, improve perfusion to vital organs SE - N & V, headache CI - V. Tach

ADRENERGIC BLOCKERS (ANTAGONISTS/SYMPATHOLYTI CS) • Block alpha & beta receptor sites (nonselective) • direct or indirect acting on the release of norepinephrine and epinephrine • Use - Cardiac arrthymias (HR), HTN ( cardiac output), angina (O2 demand) • SE - CHF, bronchospasm, bradycardia, wheezing

NONSELECTIVE VS SELECTIVE BETA BLOCKERS • Nonselective have an equal inhibitory effect on B1 & B2 receptors - - Drugs have lots of interactions due to lots of alpha/beta receptor sites throughout body - use with caution on clients with cardiac failure or asthma • Selective B1 helpful in asthma clients

ADRENERGIC BLOCKING AGENTS • • • Inderal (Propranolol) - Nonselective Use - angina, dysrhythmias, HTN, migraines SE - Many d/t nonselective CI - asthma, heart block > 1st degree Minipress (Prazosin) - A blocker Use - mild to mod. HTN SE - orthostatic hypotension Tenormin (Atenolol), Lopressor (Metoprolol) B1 (cardio) selective Use - mild to mod HTN, angina

CHOLINERGICS AND ANTICHOLINERGICS parasympathetic • Cholinergics stimulate the nervous system • Mimic the neurotransmitter acetylcholine • 2 types of cholinergic receptors 1. muscarinic - stimulates smooth muscle & slows HR 2. nicotinic - affect skeletal muscle • Many = nonselective & affect both receptors • Some affect only the muscarinic receptors and not the nicotinic receptors


CHOLINERGIC AGENTS • Direct acting - act on the receptors to activate a tissue response • Indirect acting - inhibit the action of the enzyme cholinesterase (acetylcholinesterase - ACH) • Major uses = Stimulate bladder & GI tone, constrict pupils (miosis), neuro- muscular transmission


CHOLINERGIC AGENT (PARASYMPATHOMIMETICS) • Bethanechol (Urecholine) selective to muscarinic receptors, mimic action of acetylcholine Use - For urinary retention * Take on an empty stomach d/t inc. peristalsis * Alert- Never give IM or IV – circulatory collapse, hypotension, shock & cardiac arrest poss. • Pilocarpine (Pilocar) - Ophthalmic - direct acting

CHOLINERGIC BLOCKING AGENTS ANTICHOLINERGICS/PARASYMP ATHOLYTICS • Drugs that inhibit action of acetylcholine (ACH) receptors • Affects the heart, resp. tract, GI tract, bladder, eye, & exocrine glands. • Allows the sympathetic nervous system to dominate • Anticholinergic & cholinergic drugs have opposite effects • Major responses = dec. in GI motility, dec. in salivation, dilation of pupil (mydriasis), inc. pulse rate

ANTICHOLINERGICS • Uses: Pre-op meds,bradycardia, GI/urinary antispasmodic • SE: Dry mouth/mucus membranes blocks vagal • Atropine Sulfate - Inhibits ACH effects on SA & AV nodes inc. HR inc. conduction & Use = Bradycardia, pre-up to dec. secretions, peptic ulcer disease SE = Many. Most frequent = dry mouth,

ANTICHOLINERGICS • Bentyl (Dicyclomine) - Inhibits ACH on muscarinic receptors & dec. GI motility Use - Irritable bowel syndrome SE - constipation, urinary retention, dry mouth • Robinul (Glycopyrrolate) - Similar to above Use - pre-op to dec. secretions, GI disorders SE - Similar to above

ANTICHOLINERGICS • Anticholinergics effect the CNS & benefit people prone to motion sickness • Scopolamine Patch - Classified as an antihistamine for motion sickness - Topical skin patch behind the ear x3 days Use = cruising on water, flying, car sickness Other drugs = Dramamine, Bonine SE = Dry mouth, visual disturbances d/t pupil dilation

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