Drugs Acting on the SNS Flashcards by Tyler Soulek

Occurrence and Function of Catecholamines: NE

Principal neurotransmitter
Synthesized in post-ganglionic neurons of SNS and released in adrenergic synapses
Function
- Maintenance of normal sympathetic tone
- Adjust circulatory dynamics

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Sympathomimetic Drugs: Catecholamines: Absorption and duration

Not well absorbed orally, doesn’t cross BBB

Brief duration

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Occurrence and Function of Catecholamines: EPI and DA

Stored in chromaffin granules in the adrenal medulla are released following SNS stimulation
- 75% of catecholamines released in humans is EPI
EPI
- Emergency hormone that stimulates metabolism and promotes blood flow to skeletal muscles

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Principal catecholamines in the CNS

DA and NE

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What does metyrosine inhibit

Tyrosine hydroxylase resulting in an inability to create DOPA

Used in treatment of pheochromocytoma
- Tumors synthesize huge amounts of catecholamines

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What converts DA to NE

dopamine-beta-hydroxylase

DA actively transported into vesicles for conversion

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What blocks the transport of DA and NE

Reserpine depletion of transmitter stores

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What blocks the exocytic release of NE

Guanethidine and bretylium

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What is the action of cocaine and tricyclic antidepressants

Block active NE reuptake

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How do you diagnose pheochromocytoma?

High levels of VMA and metanephrines in the urine

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Alpha receptor function

Vasoconstriction, mydriasis, contraction of sphincters of gastrointestinal and genitourinary tracts, piloerection, ejaculation

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Beta receptor functions

Vasodilation(only to skeletal muscles), bronchial relaxation, intestinal and genitourinary wall relaxation, cardiac stimulation, renin release, glycogenolysis, gluconeogenesis, lipolysis

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Beta 1 function

Cardiac stimulation

Renin release

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Beta 2

Vasodilation

Bronchodilation

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NE receptors

Alpha-1
Beta-1
Alpha-2 agonist

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EPI receptors

Alpha-1, alpha-2, beta-1, beta-2

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Isoproterenol

Beta-1, Beta-2 stimulation

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Consequence of direct cardiovascular actions

Compensatory reflex adjustments occur representing indirect drug actions

Increase BP triggers what response?

Baroreceptor discharge which inhibits SNS and activates vagal (PNS) nerve activity
Results in reflex bradycardia

Effects on Metabolism

Glycogenolysis stimulated by EPI, iso, and a little by NE
- Glucose released from liver and lactic acid released from muscle
- Mediated by beta receptors
Promote lipolysis
- Increase release of free fatty acids and glycerol from TG
- Activate TG lipase
- Mediated through beta receptor activation
Increase in metabolism

Effects on Endocrine

Renin secretion stimulation (beta-1)

Insulin secretion stimulation (beta receptors) inhibited by (alpha-2)

Effect on CNS

No effect (sympathomimetics don't cross BBB)
Indirect effect from BP response

Epinephrine: Use

Oxidation is possible converting from a clear solution to a brownish solution resulting in a decrease in potency
Allergic reaction
   - Antagonist of anaphylactic response
COPD and asthma
   - Beta-2 effect to produce bronchodilation
Local vasoconstriction
Eye
   - Mydriasis
   - Reduces IOP
Cardiac arrest (beta-1 agonist effect)
   - Could be dangerous due to cardiac necrosis due to alpha effect of vasoconstriction
   - Direct trauma
   - Arrhythmia

EPI: Adverse effects

Increase CO without improving efficiency (arrhythmias, angina, etc.)
Extavasation can result in injection site reaction leading to necrosis
- Based off alpha vasoconstriction
- Treated via an alpha antagonist
CNS
- Fear, anxiety, tenseness, restlessness, throbbing headache, tremor, dizziness
Hyperglycemia

NE (alpha1 and 2, beta 1): Use (injection)

Acute hypotensive emergencies (alpha-1 vasoconstriction) Dependent on the type of hypotension - If you have hypovolemic shock do not use - Shock - Decrease in perfusion

NE: Adverse effects

Overstimulation of the heart (beta-1)

Isoproterenol (beta-1,2): Use (Inject, inhalation; also oral and sublingual)

Bronchodilator in respiratory disorders | Cardiac stimulant in heart block, cardiogenic shock after MI, septicemic shock

Isoproterenol: Adverse effects

Tachycardia and arrhythmia Hypotension Palpitation, anxiety, headache, angina

DA (injection): Action

Beta-1 receptors in heart increase contractility and HR High doses may activate vascular alpha-1 receptors causing vasoconstriction DA receptor stimulation - Vasodilator effect on renal, mesenteric, coronary, and intracerebral vessels - Increase blood flow to kidneys

DA: uses

Shock HF ARF - Dopaminergic receptors

DA: adverse effects

Tachycardia, arrhythmias, angina, hypertension Nausea, vomitting - CTZ (chemoreceptor trigger zone) Ischemic necrosis with extravasation of large amounts

DA: Drug interactions

``` Many can oxidize CA Methenothiazine - Block dopamine effect Parkinsons drugs - Agonist ```

DA: Administration

Dispensed in aqueous solution Diluted dosage Via IV

Dobutamine: Use and mechanism

beta-1 effector | Used in HF

Other Sympathomimetics

``` Group A - Alpha adrenergic agents Group B - Mixed; direct/indirect/CNS Group C - Indirect Group D - Beta adrenergic agents ```

Group A: Agents

Alpha-1 selective agonists - Phenylephrine Alpha-2 selective - Clonidine

Phenylephrine: Action

Result of alpha-1 receptor stimulation - Vasoconstriction - Treatment of acute hypotensive conditions

Phenylephrine: Use

Treatment of paroxysmal atrial tachycardia - Vasoconstriction - Treatment of acute hypotensive conditions Reduction of regional blood flow - Hemostasis - Localizing drug at site of administration - Decongestants - Vasoconstriction of the blood vessels in the nasal mucosa Ophthalmic - Mydriasis - Glaucoma - Allergic hyperemia - Localizing site of lesion in Horner's syndrome

Clonidine: Action and use

Presynaptic | Treats glaucoma

Group B (Mixed): agents

Ephedrine | Amphetamines

Ephedrine: Use

Additive in many different preparations | Used to make meth

Ephedrine: Effects

Bronchodilator and mild stimulating properties

Amphetamines: Drug

Phenylpropanolamine - Could be used for appetite suppression however there is a rebound effect - Decongestant Push CA out of the storage vesicles and increase the amount of CA in the synapse

Group D : Beta selective agents

Beta 2 - Metaproterenol - Bronchodilator - Could be useful to delay premature delivery Beta 1 - Dobutamine - Used for its cardiac stimulation