sympathetic ns

7/31/2019 Sympathetic NS

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Sympathetic system

Releases NE from stores at nerve endings &releases E from adrenal medulla

Sympathomemtic amines as E, NE,Dopamine & Isoproternol are called

Catecholamines,


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Types of adrenergic receptors

receptors are stimulated by E & NE

Alpha 1 receptors

The image below shows the synaptic cleft,presynaptic and postsynaptic membranes.Alpha 1 receptors are located on the

postsynaptic membrane of effector organs.


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Activation of alpha 1 receptors increases vascular smooth muscle contraction, producing increases in blood presure.

Dilatation of the pupil closure of internal sphincter of the bladder .


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Alpha 2 receptors Although alpha 2 receptors are found on

presynaptic neurons, they work mainly as autoreceptors to mediate feedback inhibition of sympathetic transmission .
http://cdn.pharmacologycorner.com/wp-content/uploads/2010/07/alpha-2-receptors-synapse.gif


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1 & 2 receptors are both stimulated by

Isoprenaline & E NE acts as a 1 stimulator.

1 responses : rate & excitability of theheart with C.O.

2 responses : vasodilation,

bronchodilation, in blood glucose level,Relaxed uterine smooth muscle


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Stimulation of beta1-adrenergic receptors on themyocardium, AV node, and SA node results inCARDIAC STIMULATION:

Increased force of contraction

(positive inotropic effect)

Increased heart rate(positive chronotropic effect)


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Beta 2 receptors


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Bronchial smooth muscle

Beta 2 receptor activationpromotes bronchodilation , this

physiological property is enhanced byinhaled Beta 2 agonists used in thetreatment of asthma. Some drugs under this category include: salbutamol


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Uterine contraction

Drugs that bind to Beta 2 receptors (Beta2 agonists) are used in the treatment of premature labour, this clinical applicationillustrates how Beta 2 receptorsmediate tocolysis on the uterine muscle.Ritodrine is an example of a tocolytic drug.


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1. Direct-Acting sympathomimetics directlystimulate the adrenergic receptor (e.g.epinephrine, norepinephrine)

2. Indirect-Acting sympathomimetics whichstimulates the release of norepinephrine from

the terminal nerve endings (e.g. amphetamine)3. Mixed-Acting sympathomimetics (both direct

and indirect acting)


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Sympathomemtic Drugs

Epinephrine (E) Can be prepared synthetically Orally inactive, give by S.C. or I.M.

Actions HR & force of contraction palpitation systolic BP & little change of diastolic BP

Bronchodilation glucose level


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Therapeutic uses Anaphylactic shock Stimulates the heart in cardiac arrest Can be used to prolong local anesthetic action


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Norepinephrine (NE) Actions

both systolic & diastolic blood pressure

Uses:Treatment of shock ( BP) given by I.V.

infusion, but because of its effect

(vasoconstriction) it blood flow inessential organs tissue damage


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Isoprenaline:

Actions Bronchodilation Stimulates the heart & may produce fatal

arrhythmia Uses

Slow I.V. infusion in sever bradycardia


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Dopamine Stimulate 1 & Dopaminergic receptor.

Actions: Heart rate & force of contraction

it dilates renal arterioles blood flow tothe kidneys

Uses: Treatment of shock Treatment of congestive heart failure


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Selective Adrenergic Agonists: Selective 1 agonists: E.g. Phenylephrine, used locally as

nasal decongestant.

Selective 2 agonists: E.g. Clonidine, used for treatment of

hypertension


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Selective 1 agonists: E.g. Dobutamine, used to C.O. in

heart failure

Selective 2 agonists:

E.g. Salbutamol, used in asthma


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Indirect Acting Sympathomimetic Drugs

E.g. Amphetamine, its main effect on theCNS

MOA : NE release from presynapticterminals

It may produce euphoria, mental activity, appetite risk of dependence


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MOA of amphetamine


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Uses Narcolepsy

Hyperactivity in children Should not be used for appetite control


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Adrenergic Blockers


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Adrenergic Blockers

adrenoceptor antagonists

non selective antagonists

E.g. Phentolamine, cause BP S/Es: Postural hypotension


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Selective 1 antagonists E.g. Prazocin, Terazocin Action: Cause vasodilation, BP Uses Treatment of Hypertension Benign Prostatic Hyperplasia

S/Es commonly observed with blockers: reflex

tachycardia, vertigo, postural hypotension)


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Angina pectoris & cardiac arrhythmias.

Anxiety. Hyperthyroidism (Thyrotoxicosis) Essential Tremor.

2.Timolol Blocks 1, 2 Uses:

Topically for glaucoma


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Selective beta blockers

Atenolol Blocks 1 Beta blockers selective for these receptors

are called cardioselective beta blockers Uses

For hypertensive patients with impairedpulmonary function (but the patient should becarefully monitored)


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Labetolol: Antagonist of both 1 &

adrenoceptors


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S/Es:

1. Bronchoconstriction2. Hypotension

3. blood flow to the extremities 4. Nightmares5. Masking symptoms of hypoglycemia6. Sexual dysfunction in males


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Dental implications Xerostomia (dry mouth) Dryness of the mouth, or xerostomia, results

from diminished secretions of saliva. More than two 250 medications claimxerostomia as a side effect.

Drugs that produce xerostomia as a side effectinclude anticholinergics, antidepressants,

antihistamines/decongestants, antipsychotics,diuretics, hypnotics, systemic bronchodilators,muscle relaxants, beta-blockers ,


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Medications that produce xerostomia, also

may increase the incidence of root surfacecaries (cavities). Medications with

significant anticholinergic activity, have thepotential to cause xerostomia.

Clinical presentation of xerostomiaincludes oral fissuring, ulceration, andepithelial atrophy.

sympathetic ns

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