Adrenergic Pharmacology
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Adrenergic Pharmacology. Adrenergic receptor agonists Adrenergic recpeotr antagonists. 张纬萍 浙江大学医学院药理 2012.12.3. Brain stem or spinal cord. Pre-ganglionic neuron. Ganglionic transmitter. Post-ganglionic neuron. Neuroeffector transmitter. Effector organ. Efferent neurons of ANS.

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Adrenergic Pharmacology

  • Adrenergic receptor agonists

  • Adrenergic recpeotr antagonists




Brain stem or

spinal cord



Ganglionic transmitter



Neuroeffector transmitter

Effector organ

Efferent neurons of ANS

  • Neurotransmitters

  • Synthesis

  • Storage

  • Release

  • Inactivation

  • Receptors

  • Activation


tyrosine hydroxylase (TH)*


DOPA decarboxylase

dopamine (DA)

dopamine beta-hydroxylase (DBH)

norepinephrine (NE)

Noradrenergic Nerve:

Synthesis, storage

and release of NE

  • Uptake

  • neurotransmitter transporters

  • uptake 1: neuronal uptake

  • uptake 2: non-neuronal uptake

  • Enzymatic degradation

  • monoamine oxidase (MAO)

  • catechol-O-methyltransferease (COMT)

Norepinephrine and Epinephrine

Synthesis in the Adrenal Medulla

  • NE is stored in vesicles

  • DBH is located in vesicles

  • PNMT is located in the cytosol .

  • EPI is stored in vesicles

  • - EPI (~80%) and NE (~20%) released into blood

  • - These hormones bind adrenergic receptors on target cells, inducing the same effects as direct sympathetic nervous stimulation.







Chromaffin cell

EPI disposition: metabolism by COMT, MAO,

sulfation, uptake into NE terminals

NE Metabolism

- Within the same cells where the amines are synthesized, and in liver

- Extraneuronal O-methylation of norepinephrine and epinephrine to metanephrines represent minor pathways of metabolism.

Norepinephrine ne release
Norepinephrine (NE) release

Act on adrenergic receptors/adrenoceptors






low affinity for binding NE

G-Protein Coupled Receptors





Adrenergic Receptor Subtypes

& G-Protein Coupled Mechanisms

a1 Adrenergic Receptors:

G protein termed Gqphospholipase C activation, IP3

 mechanism: mobilizes and increases intracellular free Ca2+

 effects: primarily smooth muscle contraction

2 Adrenergic Receptors:

Inhibition of adenylyl cyclase (AC)through Gi proteins

 mechanism: decreases intracellular cAMP levels

effects: decreased protein phosphorylation, decreased cellular


b Adrenergic Receptors:

Activation of adenylyl cyclase through Gs proteins

 mechanism: increases intracellular cAMP levels

effects: phosphorylation of intracellular proteins smooth

muscle relaxation (b2), cardiac muscle contraction (b1)

Adrenergic Receptor (adrenoreceptors)

These are receptors activated by NE, EPI, or drugs with similar actions


fat cells

(not NE)

The SNS Plays a Very Important Role in the Regulation of the Cardiovascular System, which, except for the Heart, is not Innervated by the PSNS

Sns regulation of cardiac function
SNS Regulation of Cardiac Function Cardiovascular System, which, except for the Heart, is

  • The SNS innervates the entire heart while the PSNS only innervates the S-A and A-V nodes.

  • Neural modulation of heart rate occurs in part through enhancement (NE via b1 ARs) or reduction (ACh via M2R) of pacemaker activity, which is directly stimulated by elevated cAMP levels.

  • The SNS via b1 ARs also increases the force of contraction. Both heart rate and contractile force contribute to cardiac output.

Sns regulation of blood pressure
SNS Regulation of Blood Pressure Cardiovascular System, which, except for the Heart, is

  • Acute loss of SNS function lowers blood pressure

  • Chronic loss of SNS function greatly increases blood pressure variability

The SNS Enhances Cardiovascular System, which, except for the Heart, is Smooth Muscle Contraction Primarily by a1 ARs,and Reduces ContractionPrimarily by b2 ARs

Mechanisms of drug actions
Mechanisms of drug actions Cardiovascular System, which, except for the Heart, is

1.1 Direct actions on the receptors

  • Agonists

  • Antagonists

    1.2 Indirect actions via affecting transmitters

  • Synthesis (L-dopa)

  • Transport and storage (imipramine, reserpine)

  • Release (ephedrine, amphetamine)

  • Inactivation (MAOI)

Mechanisms of drug actions1
Mechanisms of drug actions Cardiovascular System, which, except for the Heart, is

1.3 Mimetics and antagonists

(1) Mimetics

direct-acting: receptor agonists

indirect-acting: increasing amounts and/or

effects of transmitters

(2) Antagonists

direct-acting: receptor antagonists

indirect-acting: decreasing amounts and/or

effects of transmitters

Drug actions and classification
Drug actions and classification Cardiovascular System, which, except for the Heart, is

Adrenoceptor agonists

  • ,  receptor agonists

  • epinephrine (adrenaline,肾上腺素),dopamine 多巴胺, ephedrine 麻黄碱

    (2)  receptor agonists

  • 12 receptor agonists:norepinephrine 去甲肾上腺素

  • 1 receptor agonists:phenylephrine苯肾上腺素

  • 2 receptor agonists:clonidine 可乐定

    (3)  receptor agonists:

  • 12 receptor agonists:isoproterenol异丙肾上腺素

  • 1 receptor agonists:dobutamine 多巴酚丁胺

  • 2 receptor agonists:salbutamol 沙丁胺醇

Structure-activity relationship of Cardiovascular System, which, except for the Heart, is

catecholamines and related compounds

Sympathomimetic amines Cardiovascular System, which, except for the Heart, is

  • Non-catecholamine

  • Indirect-acting by causing the release of stored catecholamine.

  • Not inactivated by COMT; some are poor substrate for MAO

    (orally active, a prolonged duration of action)

  • Greater access to the CNS

  • Catecholamine

  • High potency in activating a or b receptors

  • Rapid inactivation by COMT and by MAO

  • Poor penetration into the CNS

The mode of action Cardiovascular System, which, except for the Heart, is

of sympathomimetic drugs

  • Direct mode

  • e.g. Norepinephrine

  • epinephrine

  • isoproterenol

  • Indirect mode

  • Mixed mode

  • e.g. ephedrine

  • Enhances release of stored catecholamines

    e.g. amphetamine

  • Inhibition of reuptake of released catecholamines

    e.g. cocaine

  • Inhibition of MAO

    e.g. pargyline

Epinephrine, Cardiovascular System, which, except for the Heart, is Adrenaline: DIRECT

Pharmacological effects

1, 2 , 1 , 2 receptor agonists

(1) Cardiac effects

  • 1: contractility  (positive inotropic),

    HR  (positive chronotropic),

    cardiac output ,

    oxygen consumption ,

    inducing arrhythmia

    (2) Vascular effects (cerebral and renal circulation)

  • 1:vasoconstriction (skin, mucous, viscera),

    especially at larger doses

  • 2:vasodilatation of skeletal muscles

    and coronary vessels

Concentration-dependent response in vascular smooth muscle to epinephrine

Predominant Effects

low [EPI] β2 > α

high [EPI] α > β2

Epinephrine, to epinephrine Adrenaline: DIRECT

(3) Blood pressure

  • Systolic BP , Diastolic BP ↓(slight)

    (4) Respiratory

  • 2:dilatation of bronchial smooth muscles


  • 1:reducing congestion and edema of

    bronchial mucosa

    (5) Metabolic effects

  • blood glucose  (hyperglycemia);

    free fatty acids  (lipolysis)

Effects of epinephrine to epinephrine(therapeutic doses)

systolic pressure due to increased cardiac contractile force and a rise in cardiac output .

diastolic pressure usually falls due to the decrease of peripheral resistance decreasing.

1 in heart, 1 in many microvessels, 2 in the vessels of skeletal muscle

Epinephrine, to epinephrine Adrenaline: DIRECT

(6) Smooth muscle

  • Effects on vascular smooth muscle are of major physiological importance.

  • GI smooth muscle, relax (, )

  • Stomach, relax

  • Pyloric and ileocecal sphincters, contracted (depends on the pre-existing tone of the muscle).

  • Uterine, differ upon the time

  • Detrusor muscle(逼尿肌) of the bladder, contraction

Epinephrine, to epinephrine Adrenaline: DIRECT

Clinical uses

Systematic uses:

Cardiac arrest

Anaphylactic shock

Acute bronchial asthma

Topical uses:

Adjuvant of local anesthesia


Epinephrine, to epinephrine Adrenaline: DIRECT

Adverse effects

(1) Cardiac arrhythmias

(2) Hemorrhage (cerebral or subarachnoid):

reason: a marked elevation of BP

(3) Central excitation:anxiety, headache...

(4) Contraindications: heart diseases, hypertension, coronary arterial disease, arteriosclerosis, hyperthyroidism. Esp. patients receiving nonselective  blockers.

Norepinephrine to epinephrine, Noradrenaline, NE: DIRECT

Pharmacological effect

1, 2 receptor agonists

NE and Epi are similar potent on 1

NE has little action of 2

(1) Vascular effects:

1:vasoconstriction (skin, renal, brain,

hepatic, mesenteric, etc.), blood flow 

2:inhibiting NE release

Actions of norepinephrine on post-synaptic ( to epinephrine1) and pre-synaptic (2 ) receptors

Norepinephrine to epinephrine, Noradrenaline: DIRECT

(2) Blood pressure:

  • Systolic BP , Diastolic BP (especially at larger doses)

    (3) Cardiac effects:

  • Weak direct stimulation (1); inhibition via reflex(in vivo)

  • Net result: little cardiac stimulates

Effects of catecholamines to epinephrine(therapeutic doses)

  • Predominant Effects: BP, peripheral resistance, HR

  • 1 receptor: vascular smooth muscle contraction

  • 1 receptor: myocardial contraction

Norepinephrine to epinephrine, Noradrenaline: DIRECT

Clinical uses (limited therapeutic value)

(1) Shock

  • used in early phase of some types of shock: small doses and shorter duration

    (dopamine is better; replaced by Metaraminol,间羟胺)

    (2) Hypotension due to drug poisoning

  • especially for chlorpromazine

    (3) Hemorrhage in upper alimentary tract,上消化道出血

  • orally given after dilution

Norepinephrine to epinephrine, Noradrenaline: DIRECT

Adverse effects

(1) Ischemia and necrosis at the site of iv administrationrelieved by filtrating the area with phentolamine (receptor antagonist)

(2) Acute renal failureavoiding larger doses and longer duration; monitoring urinary volume

(3) Contraindicationhypertension, arteriosclerosis, heart diseases, severe urinary volume , microcirculation disorders

Dopamine: to epinephrineDIRECT

Pharmacological effects :

,  receptor, dopaminergic receptor agonists

(1) Cardiac effects:1 receptor, weak

(2) Vascular effects:

DA receptor:vasodilatation of renal and mesenteric arteries , blood flow (small doses);

1 receptor:vasoconstriction of skin, mesenteric vessels (larger doses)

(3) Renal effects:renal vasodilatation; natriuretic effects

Dopamine to epinephrine,DIRECT

Clinical uses

(1) Shock, sever congestive failure

  • cardiac and septic shock

    (2) Acute renal failure

  • combined with furosemide

    Adverse effects – short-lived

  • tachycardia, arrhythmia, reduction in urine flow (renal vasoconstriction)

L-DOPA but not dopamine can enter brain.

Isoproterenol to epinephrine,

Isoprenaline: DIRECT


1 , 2 receptor agonists

(1) Cardiac effects (1 receptor)

(2) Vascular effects

2 receptor:dilatation of skeletal muscles and coronary vessels;

SP ,DP  or ,pulse pressure 

(3) Bronchodilatation (2 receptor)

(4) Metabolism

Promoting effects as epinephrine

Effects of catecholamines to epinephrine(therapeutic doses)

Predominant Effects: HR, systolic BP, distolic BP, peripheral resistance 

1, myocardial contraction

2, vascular dialization

, at higher concentrations

Isoproterenol to epinephrine, Isoprenaline

Clinical uses

(1) Cardiac arrest / A-V block: in emergencies

(2) Shock / Bronchial asthma: replaced by

other sympathomimetics

Adverse effects

(1) Heart stimulation, arrhythmia

(2) Contraindications:coronary heart

disease, myocarditis, hyperthyroidism,


to epinephrine1 receptor agonists

  • Heart failure (after cardiac surgery or congestive HF or acute myocardial infarction; short-term treatment)

  • Cardiac stimulation

    (-) isomer of dobutamine is a potent agonist at 1 receptors

    (+)-dobutamine is a potent 1 receptor antagonist


to epinephrine2 receptor agonists


  • Uses:

    Bronchial asthma

    Dilation of bronchial smooth muscle; 2 > 1 agonist (partially selective): preferential activation of pulmonary 2 receptors by inhalation.

    Premature Labor (combine with ritodrine,羟苄羟麻黄碱).

  • Adverse effects:

    headache, cardiac stimulation and skeletal muscle fine tremor (2 receptors on presynaptic motor terminals; their activation enhances ACh release).

Terbutaline to epinephrine:博利康尼






to epinephrine2 receptor agonists








to epinephrine1 receptor agonists

Methoxamine(伐沙克新): DIRECT>INDIRECT

Phenylephrine(苯肾上腺素): DIRECT>INDIRECT

  • Induces reflex bradycardia, used in hypotension, paroxysmal supraventricular tachycardia ;

  • Phenylephrine: Mydriasis(瞳孔散大), pupillary dilator muscles, no or less effect on intraocular pressure, short-acting (for several hours); act as a nasal decongestant

to epinephrine2 receptor agonists


  • Uses: antihypertensive drug; can be administered as transdermal patch (permits continuous administration)

  • Mechanism of action : α2-adrenergic partial agonist; actions predominantly in CNS. Lowers blood pressure by inhibiting sympathetic vasomotor tone (probably on I1 receptor).

  • Adverse effects: (iv administration may result in transient increase in blood pressure (activation of post-synaptic receptors); dry mouth, sedation

Other  to epinephrine2 receptor agonists

Apraclonidine, 阿拉可乐定

Brimonidine, 溴莫尼定

Guanfacine, 氯苯乙胍

Guanabenz, 氯苄氨胍

Methyldopa, 甲多巴

Tizanidine, 替扎尼定

Ephedrine: to epinephrine麻黄碱,MIXED



  • Promoting the release of NE, weak agonist effectson 1、2、1、2 receptors


  • chemically stable, orally effective;

  • less potent but longer action duration;

  • central stimulating: alertness , fatigue ↓, prevents sleep (adverse effects)

  • Tachyphylaxis (快速抗药反应).

Ephedrine to epinephrine

Clinical uses

(1) Prevention of hypotension:anesthetics

(2) Nasal decongestion:nasal drop,如感冒

(3) Bronchial asthma:mild, chronic cases

(4) Relieving allergic disorders:urticaria(荨麻

疹), angioneurotic edema

INDIRECT to epinephrine-acting drugs (summary)

Drug actions and classification1
Drug actions and classification to epinephrine

Adrenoceptor agonists

  •  receptor agonists

  • epinephrine (adrenaline,肾上腺素),dopamine 多巴胺, ephedrine 麻黄碱

    (2)  receptor agonists

  • 12 receptor agonists:norepinephrine 去甲肾上腺素

  • 1 receptor agonists:phenylephrine苯肾上腺素

  • 2 receptor agonists:clonidine 可乐定

    (3)  receptor agonists:

  • 12 receptor agonists:isoproterenol异丙肾上腺素

  • 1 receptor agonists:dobutamine 多巴酚丁胺

  • 2 receptor agonists:salbutamol 沙丁胺醇

Adrenergic receptor antagonists
Adrenergic Receptor Antagonists to epinephrine

  • Antagonist characteristics

  • receptor occupancy (binding affinity)

  • no receptor activation (no efficacy)

  • Antagonists of NE at either a or b receptors

  • - competitiveantagonists (reversible), blocking endogenous norepinephrine

  • - irreversible antagonists

  • nonselective and selective drugs available for both the a or b receptors.

Drug actions and classification2
Drug actions and classification to epinephrine

Adrenoceptor antagonists

(1) receptor antagonists

  • 12 receptor antagonists:

    short-acting: phentolamine,酚妥拉明

    long-acting: phenoxybenzamine,酚苄明

  • 1 receptor antagonists:prazosin,哌唑嗪

  • 2 receptor antagonists:yohimbine,育亨宾

Drug actions and classification3
Drug actions and classification to epinephrine

Adrenoceptor antagonists

(2) receptor antagonists

  • 12 receptor antagonists:propranolol,普萘洛尔

  • 1 receptor antagonists:atenolol,阿替洛尔

  • 2 receptor antagonists:butoxamine,布托沙明

    (3),  receptor antagonists

  • labetalol,拉替洛尔

epinephrine to epinephrine

 antagonist



Epinephrine reversal

(adrenaline reversal)

Phentolamine to epinephrine

  • competitive, nonselective(1, 2 receptor antagonists, block 5-HT release)

Pharmacological effects

(1) Vasodilatation

Blocking 1 receptor: vasodilatation in both arteriolar

resistance vessels and veins

(2) Cardiac Stimulation

Reflex;blocking 2 receptor ~NE release 

(3) Cholinergic and histamine-like effects

Contraction of GI smooth muscles,

Gastric acid secretion 

Phentolamine to epinephrine

Clinical uses

(1) Hypertension from pheochromocytoma (short term use).

  • Pre- and post-operation of pheochromocytoma

    • Diagnostic test for pheochromocytoma

    (2) Peripheral vascular diseases

  • Acrocyanosis, Raynaud’s disease

    (3) Local vasoconstrictor extravasation

    Major Adverse effects– postural hypotension, reflex tachycardia, arrhythmia, angina pectoris, GI reactions

Pheochromocytoma to epinephrineis a rare catecholamine-secreting tumor derived from chromaffin cells of the adrenal medulla that produces excess epinephrine.

  • Hypertension & Crises

  • Elevated Metabolic Rate

    -heat intolerance

    -excessive sweating

    -weight loss

  • Temporarily manage with

    -adrenergic antagonists (a1 & ±b)

Phenoxybenzamine to epinephrine

  • Irreversible, nonselective ( 1 and 2 antagonists )

  • Long-acting

  • Similar to phentolamine in actions and clinical uses

to epinephrine1 receptor antagonists

Prazosin(哌唑嗪): treatment for hypertension

Tamsulosin (坦索罗辛): treatment for benign prostatauxe (to relief the difficulty of urination)

Terazosin (特拉唑嗪): less potent than prazosin, but retains high specificity for 1

Doxazosin (多沙唑嗪): similar as prazosin, but has longer duration of action.

Alfuzosin (阿夫唑嗪): structure not related.

Adverse effects of  to epinephrine1 receptor antagonists

First-dose effect, marked hypotension,

Syncope (晕厥)

Clinically,these drug are used for the patient with hypertentsion and benign prostatic hyperplasia (良性前列腺肥大)

2 receptor antagonists

Yohimbine: for research use only

 receptor antagonists to epinephrine


  • First-pass elimination,

    low bioavailability: propranolol(普萘洛尔)

  • Hepatic metabolism and renal excretion, hepatic and renal functions alter the effects of the drugs and result in large individual variation

  • So, dose individualization is necessary.

Effects of an b ar antagonist
Effects of an to epinephrineb AR Antagonist

 receptor antagonists to epinephrine

Pharmacological effects

(1)  receptor blockade

A. Cardiovascular effects:

Depressing heart: reduction in HR, A-V conduction, automaticity, cardiac output, oxygen consumption

Hypotension: peripheral blood flow , hypertensive effects in hypertensive patients

 receptor antagonists to epinephrine

(1)  receptor blockade

B. Bronchial smooth muscles (2)

Induces bronchial smooth muscle contraction in asthmatic patients

C. Metabolism (2 and 3)

Lipolysis(脂解作用)  , glycogenolysis(糖原分解)  , classical blockers decreasing while novel blockers potentiating insulin effects ~ hypoglycemia(低血糖)。

D. Renin secretion (1)

Decreasing secretion of rennin

 receptor antagonists to epinephrine

(2) Intrinsic sympathomimetic effects

Partial agonists: e.g. pindolol,acebutolol

(3) Membrane-stabilizing effects

Larger doses of some drugs: quinidine-like

effects, Na+ channel block

(4) Others

Lowering intraocular pressure;

Inhibiting platelet aggregation

 receptor antagonists to epinephrine

Clinical uses

(1) Arrhythmia:supraventricular, sympathetic activity 

(2) Hypertension

(3) Angina pectoris and myocardial infarction


(4) Chronic heart failure

(5) Others: hyperthyroidism, migraine, glaucoma(timolol)

The use of beta adrenergic blocking agents in heart failure
The Use of Beta Adrenergic Blocking to epinephrineAgents in Heart Failure




LVEF % change









Time (weeks)

Initial hemodynamic deterioration followed by reverse remodeling (decrease in EDV and ESV) with improved ventricular function over time (increased LVEF


Blockers differ in their long term effects on mortality in hf
to epinephrine-Blockers Differ in Their Long-Term Effects on Mortality in HF




Metoprolol tartrate6

Metoprolol succinate7




No effect


Not well studied


No effect


1CIBIS II Investigators and Committees. Lancet. 1999;353:9-13. 2The BEST Investigators. N Engl J Med 2001; 344:1659-1667. 3Colucci WS, et al. Circulation 1996;94:2800-2806. 4Packer M, et al. N Engl J Med 2001;344:1651-1658. 5The CAPRICORN Investigators. Lancet. 2001;357:1385-1390. 6Waagstein F, et al. Lancet. 1993;342:1441-1446. 7MERIT-HF Study Group. Lancet. 1999;353:2001-2007. 8SENIORS Study Group. Eur Heart J. 2005; 26:215-225. 9The Xamoterol in Severe heart Failure Study Group. Lancet. 1990;336:1-6.

 receptor antagonists to epinephrine

Adverse effects

(1) Heart depression: contraindicated in heart failure, severe A-V block, sinus bradycardia

(2) Worsening of asthma: contraindicated in bronchial asthmatic patients

(3) Withdrawal syndrome:up-regulation of the receptors

(4) Worsening of peripheral vascular constriction

(5) Others:central depression, hypoglycemia,etc.

Propranolol to epinephrine

  • 1, 2 receptor blocking

  • no intrinsic activity

  • first-elimination after oral administration, individual variation of bioavailability


  • For treatment of glaucoma (wide-angle)

Atenolol, Metoprolol to epinephrine

  • 1receptor antagonists, no intrinsic activity

  • Atenolol : longer t1/2, once daily

  • Usually used for treatment of hypertension

to epinephrineNO, 2 agonist,

1 blocker Ca2+ blocker Antioxidation

1 blocker



α, to epinephrine receptor antagonists


  • α, β receptor blocking, β> α

  • usually used for treatment of


summary to epinephrine

summary to epinephrine

summary to epinephrine

Therapeutic Uses of to epinephrinea1 (±b) AR Agonists

1. Hypotension(低血压)

  • Preserve adequate blood perfusion to heart, brain or kidneys in cases of hemorrhage, overdose of antihypertensive drugs or spinal cord injuries.

  • Short duration of treatment: NE, phenylephrine, methoxamine, ephedrine (a1 AR agonists).

2. Shock(休克)

  • Inadequate perfusion to tissues as a consequence of hypovolemia, cardiac failure, or altered vascular resistance.

  • Usually associated with hypotension.

  • Use of a1-adrenergic agonists to increase peripheral vascular resistance, and b1-adrenergic agonists to improve cardiac function.

3. Cardiogenic Shock(心源性休克)

  • Massive myocardial infarction.

  • Stimulation of cardiac b1-adrenergic receptors is needed: isoproterenol, norepinephrine, epinephrine, dobutamine, dopamine.

Therapeutic Uses of to epinephrinea1 (±b) AR Agonists

4. Local Vascular Effects(局部的血管变化)

- Reduction of regional blood flow in surgery (nose, throat, larynx) to improve visualization by limiting hemorrhage.

- Epinephrine retards the absorption of local anesthetics and increases the duration of anesthesia (vasoconstrictor effect of epinephrine)

5. Nasal Decongestion(鼻腔充血)

- a1-Adrenergic agonists are used as nasal decongestants.

- These drugs decrease the volume of the nasal mucosa and therefore reduce the resistance to airflow.

- Oxymetazoline, phenylephrine and ephedrine are commonly used.

6. Allergic Reactions(过敏反应)

- Epinephrine (s.c.) is used in acute hypersensitivity reactions.

- Activation of b-adrenergic receptors on mast cells suppresses the release of histamine and leukotrienes.

Therapeutic Uses of to epinephrineb2 AR Agonists

1. Asthma(哮喘)

- Asthma is a condition of overreactive airways. Asthma attacks can make it very difficult to breath because of excess bronchoconstriction.

- b2 AR agonists such as albuterol, metaproterenol and terbutaline are used.

- The drugs are administered by inhalation and are absorbed slowly, limiting their systemic side effects, and b2 selectivity reduces cardiac stimulation.

2. Premature Labor(早产)

- When labor occurs prematurely (before 37 weeks), it is a risk to the fetus.

- b2 AR agonists relax the smooth muscle of the uterus and help prevent premature delivery. The goal is to reach at least 37 weeks when the fetal lungs have matured.

Therapeutic Uses of to epinephrinea1 & b AR Antagonists

1. Pheochromocytoma(肾上腺嗜铬细胞瘤)

2. Hypertension(高血压)

- While not commonly used anymore, a1 blockers can be use to treat hypertension.

- Somewhat more common is the use of b blockers. These work centrally (the most important effect – the mechanism is not completely understood) and peripherally (decrease heart rate some).

3. Heart Failure(心功能衰竭)

- After a myocardial infarction, the SNS will be activated to increase the cardiac output from the remaining good heart tissue. This is good in the short-term, but long-term changes lead to cardiac hypertrophy and failure.

- Ironically, b blockers reduce the incidence of sudden death from heart failure.