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adrenergic agonists
| Term | Definition |
|---|---|
| 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 |
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ahmad445
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