The Adrenergic System Flashcards
(39 cards)
neurotransmitters of the adrenergic system are
catecholamines -
adrenaline and noradrenaline.
catecholamines -
adrenaline and noradrenaline.
( physiology - mechanism )
+ look the steps from pic of atlas
1) - They are synthesized in the cytoplasm of cells adrenergic neurons from tyrosine which converts in dopa (by tyrosine hydroxilase ) , an amino acid which then transforms into dopamine. ( tyrosine -> DOPA -> DOPAMINE )
2) Dopamine -> NE (noradrenaline) which
is converted into -> epinephrine (adrenaline).
3) Catecholamines are released from the deposit granules by exocytosis.
4) From the synaptic cleft it diffuses and stimulate specific receptors - adrenergic receptors.
5) Termination of the effect of catecholamines is done by passive diffusion,
reuptake and metabolism by 2 enzymes - monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT)
Sympathomimetics
Agents that activate adrenergic receptors
Sympatholytics
Agents that blocks the activation of adrenergic receptors
Adrenergic receptors
G protein coupled receptors and are of two
types - α and β.
α-adrenergic receptors:
- postsynaptic α1 receptors
- presynaptic, postsynaptic and extrasinaptic α2 receptors.
adrenergic receptors G coupled + production of 2nd messenger
α1 receptors are coupled with Gq proteins. -> ACTIVATES : phospholipase C , producing IP3 & DAG
α2 receptors are coupled with Gi proteins -> INHIBIT : adenyl cyclase , decreasing cAMP formation
β-adrenergic receptors are coupled with Gs proteins -> STIMULATE : Adenyl cyclase with an increase in intracellular cAMP
β-adrenergic receptors -
β1, β2, β3
Effects of adrenergic receptor stimulation
α1 receptors: (6)
VASCULAR LEVEL : o vasoconstriction, (thus ↑BP); o decreased bronchial secretion , o mydriasis, GI LEVEL : o spleen capsule contraction, o piloerection, o decreased insulin secretion.
presynaptic α2 receptors:
decreases the release of norepinephrine into the synaptic cleft -
feedback mechanism. ( negative feedback)
- inhibition of neurotransmitter release ( noradrenaline + acetylcholine )
α2 postsynaptic receptors:
Vasoconstriction
extrasynaptic α2 receptors:
o stimulates platelet aggregation
+ contraction of vascular smooth muscles
+ inhibition of insulin release
β1 receptors:
increases the activity of the heart (increases contractility, A-V conduction, excitability)
o stimulates renin secretion
- CNS = anxiety
β2 receptors:
o vasodilation, ( in skeletal muscle ) o bronchodilation, o relaxes uterine muscles, o tremor, o agitation, o nervousness, o increases gluconeogenesis and glycogenolysis, o increases insulin secretion
β3 receptors:
o lipolysis and glycogenolysis.
Direct sympathomimetics
are substances that have affinity for
adrenergic receptors and intrinsic activity
Adrenaline
- stimulates all adrenergic receptors.
Effects: - anxiety, insomnia, nervosity, vasoconstriction in the
subcutaneous, splanchnic and renal territories and - vasodilation in the muscular,
cardiac and cerebral territories, stimulation of the heart. - Systolic blood pressure
rises, - diastolic blood pressure does not change. - Bronchodilation.
Indications.
- anaphylactic shock. - type I hypersensitivity reactions
- acute asthma attack.
- cardiac arrest
- antihemorrhagic in association with local anesthetics.
Side effects: increased blood pressure with strokes, severe heart arrhythmias, ventricular fibrillation, worsening of ischemic heart disease,
myocardial infarction, tremor of the extremities, anxiety, psychomotor agitation
Noradrenaline ( Norepeinephrine )
- stimulates α adrenergic receptors;
- no β adrenergic effects.
- Effects:
1) vasoconstriction in all territories,
2) contraction of the spleen capsule.
3) Increases blood pressure, both systolic and diastolic.
Indications :
hypovolemic shock with collapse
- administration by intravenous infusion
Dopamine
- stimulates adrenergic and dopaminergic receptors
- Effects:
1) vasodilation in the splanchnic and renal territory.
2) In high doses the drug can stimulate : - β1 adrenergic receptors by increasing heart activity
- α adrenergic receptors by increasing blood pressure.
Indications: selected cases of shock in intravenous infusion.
Isoprenaline
Dilation
- selective β1 and β2 receptors agonist.
- Effects:
o bronchodilation,
o heart stimulation,
o vasodilation,
o decreases diastolic blood pressure and increases systolic blood pressure.
Side effects
- worsening of ischemic heart disease,
- acute myocardial infarction,
- ventricular fibrillation, tachycardia, palpitations,
- extremity tremor,
- psychomotor agitation, anxiety
Selective α1 sympathomimetics
phenylephrine, ethylephrine -
produce vasoconstriction; used in the treatment of particular types of shock or
as a decongestant of the nasal or conjunctival mucosa (local applications)
Selective α2 sympathomimetics
clonidine - lowers blood pressure -
is used to treat high blood pressure.
Selective β1 sympathomimetics
dobutamine - increases the
contraction force of the myocardium, increases the cardiac output; used in cardiogenic shock
Selective β2 sympathomimetics
1) salbutamol,
2) phenoterol,
3) orciprenaline,
4) terbutaline,
5) salmeterol
produce bronchodilation, vasodilation
and relaxation of the uterine smooth muscles. Indications: treatment of asthma,
treatment of painful uterine contractions in pregnant women.
* Inhalatory , oral , injectable ( terbutaline )
EFFECTS :
- Low-intensity cardiac side effects, * ( angina , tachycardia ,arrythmia - β1 rec activation )
- tremor of the extremities,
- increased excitability of the central nervous system,
- anxiety.
