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adrenergic agonists

Sympathomimetics 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)
α-Adrenoceptors -itsaffinity is epinephrine ≥ norepinephrine >> isoproterenol -two subgroups, α1 and α2 "/affinity to agoinst@antagonist" ex-.α1 have a higher affinity for phenylephrine than α2. the drug clonidine selectively binds to α2
α1 Receptors -on postsynaptic membrane of the effector organs -act via G protein activation of phospholipase C,which produce 2nd messenger IP3 & DAG. -
α2 Receptors: -on sympathetic presynaptic nerve endings and control the release of norepinephrine. -Stimulation of α2 receptors causes feedback inhibition inhibits further release of norepinephrine -local mechanism for modulating norepinephrine output -acting as in
α2 Receptors: -found on presynaptic parasympathetic neurons. -inhibiting acetylcholine release -activation α2 receptors cause inhibition of adenylyl cyclase and decrease cAMP
tamsulosin is a selective α1A antagonist that is used to treat benign prostatic hyperplasia. - has fewer cardiovascular side effects -α1A receptors found primarily in the urinarytract and prostate gland -does not affect the α1B in the blood vessels
β-Adrenoceptors -potency is isoproterenol > epinephrine > norepinephrine -three major subgroups, β1, β2, and β3 β1 have equal affinities for epinephrine and NE β2 have a higher affinity for epinephrine than for NE
β3 receptors involved in lipolysis and also have effects on the detrusor muscleof the bladder. -Binding of a NT at any of the three types of β receptors results in activation of adenylyl cyclase and increased concentrations of cAMP within the cell.
... the vasculature of skeletal muscle have both α1 and β2 receptors, but the β2 receptors predominate. - Other tissues may have one type of receptor almost exclusively. ex, the heart contains predominantly β1 receptors.
Major effects mediated by α- and β-adrenoceptors photo
Desensitization of receptors: 1) sequestration of the receptors so unavailable for interaction with the ligand; 2) down-regulation, by destruction or by decreased synthesis; 3) inability to couple to G protein, because the receptor has been phosphorylated on the cytoplasmic side.
Two important structural features of ADRENERGIC AGONISTS 1) the number and location of OH substitutions on the benzene ring 2) the nature of the substituent on the amino nitrogen
Catecholamines -contain the 3,4-dihydroxybenzene group -epinephrine, norepinephrine, isoproterenol, and dopamine -1. High potency.. in directly activating α or β receptors -2. Rapid inactivation:metabolized by COMT postsynaptically and by MAO intraneuronally. -given
Noncatecholamines lacking the catechol hydroxyl groups have longer halflives,they are not inactivated by COMT -include phenylephrine,ephedrine, and amphetamine -are poor substrates for MAO (an important route of metabolism -greater access to the CNS
Substitutions on the amine nitrogen -important indetermining β selectivity -epinephrine,with a –CH3 substituent -isoproterenol, which has an isopropyl substituent -
Direct-acting adrenergic agonists -act directly on α or β receptors, producing effects similar to those of epinephrine -ex.epinephrine,norepinephrine, isoproterenol, and phenylephrine
Indirect-acting agonists: -may block the reuptake of norepinephrine or cause the release of norepinephrine from the cytoplasmic pools or vesicles of the adrenergic neuron -ex-cocaine and amphetamines
Mixed-action agonists: Ephedrine and its stereoisomer, pseudoephedrine, both stimulate adrenoceptors directly and release norepinephrine from the adrenergic neuron
Epinephrine administered : subcutaneous, inhalation,eye, drops ,intracardiac -In the adrenal medulla, norepinephrine is methylated to yield epinephrine, which is stored in chromaffin cells along with norepinephrine -80% epinephrine and 20% norepinephrine directly i
Actions of Epinephrine similar to sympathetic stimulation Cardiovascular system  Heart : ↑all cardiac properties (↑contractility, heart rate , AV conduction, excitability, automaticity  Blood vessels: • Vasoconstriction (skin, mucous membrane, renal) • Vasodilatation (skeletal muscle, coronary blood vessel
Actions of Epinephrine similar to sympathetic stimulation Respiratory system:  Bronchodilatation (β2)  Decongestion of bronchial mucosa (α1) urinary bladder and Gastrointestinal tract : Spasm of spincters (α1)  Relaxation of the wall (β2) urinary retention and inhibits defecation
Actions of Epinephrine similar to sympathetic stimulation - Skeletal muscle  Facilitate NM transmission  Vasodilatation (β2) -Eye  Vasoconstriction of conjunctival blood vessels (decongestion)  ↓intraocular pressure  Mydriasis -Antiallergic Adrenaline is Physiological antagonist of histamine --Metabolism
Adrenaline Uses  With local anesthetic (delay absorption and prolong duration of drugs)  Open angle glaucoma (eye drops)  Epistaxis (haemostatic nasal pack)  Anaphylactic shock  Cardiac resuscitation in cardiac arrest  Acute bronchial asthma
Pharmacokinetics of Epinephrine -rapid onset but a brief duration of action -The preferred route is intramuscular (anterior thigh) -rapidly metabolized by MAO and COMT, -the metabolites metanephrine and vanillylmandelic acid are excreted in urine.
-Adverse effects of Epinephrine -CNS effectsthat" anxiety, fear, tension, headache, and tremor" -Tachycardia, palpitation, angina and arrhythmia -induce pulmonary edema. -In diabetic patients, dosages of insulin may have to be increased.
Contraindications of Epinephrine  Injection Around finger or toe  Hypertension  coronary heart disease  Arrhythmia  Hemorrhagic shock  Thyrotoxicosis
Norepinephrine -α-adrenergic receptor is most affected. -Neurotransmitter released from postganglionic adrenergic nerve endings (80%) -Orally ineffective and poor SC absorption -IV administered -Metabolized by MAO, COMT ..Short duration of action
Actions -Agonist at α1(predominant), α2 and β1 Adrenergic receptors No effect on β2 -Increases systolic, diastolic B.P, mean pressure, pulse pressure and stroke volume -Total peripheral resistance (TPR) increases due to vasoconstriction - Pressor agent Incre
uses Norepinephrine used as a vasopressor agent in treatment of hypovolemic shock and other hypotensive states in order to raise B.P
-Adverse effects of norEpinephrine -Anxiety, palpitation, respiratory difficulty -Acute Rise of BP, headache -Extravasations causes necrosis, gangrene
Isoprenaline ....isoproterenol -Catecholamine acting on beta-1 and beta-2 receptors Overall effect is Cardiac stimulant (beta-1) -Increase in SBP but decrease in DBP (beta-2) -Decrease in mean BP -potent Bronchodilatation -Used as Bronchodilator and for treatment of AV block -daw
Dopamine Immediate metabolic precursor of Noradrenalin High concentration in CNS - basal ganglia, limbic system and hypothalamus and also in Adrenal medulla Central neurotransmitter, regulates body movements ineffective -orally, IV use only, Short T 1/2 (3-5min
MECHANISM OF Dopamine -Agonists at dopaminergic D1, D2 receptors -Agonist at adrenergic α1 and β1 stimulates-- D1-receptors in renal, mesenteric and coronary vessels leading to vasodilatation . -D2 receptors (present in presynaptic adrenergic neurones) suppression of NA re
actions -Cardiovascular: stimulatory effect on heart, positive inotropic and chronotropic <β1>. At very high doses, dopamine activates α1 resulting in vasoconstriction. -Renal and visceral: Dopamine dilates renal and splanchnic arterioles by D1&D2
therapeutic use -drug of choice for cardiogenic and septic shock and is given by continuous infusion. -It raises blood pressure -enhances perfusion to the kidney and splanchnic areas -used to treat hypotension and severe heart failure,
Adverse effects: - as sympathetic stimulation. Dopamine is rapidly metabolized by MAO or COMT, (nausea, hypertension,and arrhythmias)
Fenoldopam [fen-OL-de-pam] is an agonist of peripheral D1 receptors. -used as a rapid-acting vasodilator to treat severe hypertension in hospitalized patients -act coronary arteries,kidney arterioles, and mesenteric arteries. -undergoes extensive first-pass metabolism and has
Dobutamine [doe-BYOO-ta-meen] is a synthetic, direct-acting catecholamine that is a β1 receptor agonist. It increases cardiac rate and output with few vascular effects. - used to increase cardiac output in acute heart failure &inotropic support after cardiac surgery . The drug increases cardiac output and does not significantly elevate oxygen demands of
Oxymetazoline -stimulates both α1- and α2. - found in many over-the-counter short-term nasal spray decongestants,& ophthalmic drops for the relief of redness -It is absorbedin the systemic circulation regardless of the route of administration and may produce nervous
Phenylephrine [fen-ill-EF-reen] -binds primarily to α1 receptors. Phenylephrine is a vasoconstrictor that raises both systolic and diastolic blood pressures. - It has no effect on the heart but induces reflex bradycardia The drug is used to treat hypotension in hospitalized or surgi
Created by: ahmad445