SNS agonists Flashcards
1
Q
Unwanted effects of adrenaline
A
SIDE EFFECTS NOT SEVERE UNLESS PATIENT ALREADY HAS AN UNDERLYING PROBLEM
- Secretions->reduced and thickened mucous
- CNS->minimal effect
- Gastrointestinal tract->minimal
- Skeletal muscle->tremor (noradrenaline aids skeletal muscle contraction to give tremor)
- CVS (effect dependent on age and what normal CVS function looks like)->tachycardia, palpitations, arrhythmias, cold extremities (vasoconstriction of peripheral vessels so blood cannot permeate peripheral regions of the body) , hypertension etc (adrenaline overdose results in cerebral haemorrhage, pulmonary oedema etc)
2
Q
Adrenaline
A
- Non-selective agonist
- emergency hormone preparing for fright, flight or fight response
3
Q
Clinical uses of adrenaline
A
- treatment of allergic reactions and anaphylactic shock
- spinal anaesthesia
- local anaesthesia
- acute bronchospasm associated with chronic bronchitis or emphysema
- asthma (in emergencies-i.m. or s.c.)
- cardiogenic shock
4
Q
Phenylephrine
A
- more selective for alpha 1 receptors (alpha1 selective agonist)-> alpha1»alpha2»>beta1/beta2
- chemically (and structurally) related to adrenaline but more resistant to COMT(more peripheral enzyme), not MAO (more central enzyme)
- structurally different from adrenaline in terms of single hydroxyl group->enables phenylephrine to be more alpha selective and more resistant to breakdown compared to adrenaline
5
Q
Clinical uses of Phenylephrine
A
-vasoconstriction (i.v. or topical administration)->main purpose of alpha1 agents
mydriatic eye drops (induce pupil dilation)
-nasal decongestant->mucous production from white cell infiltration into nasal sinus (white cell accumulation causes oedema, fluid leakage etc), thus phenylephrine stimulates the sympathetic system to cause vasoconstriction which leads to less white cell infiltration and fluid exudation
6
Q
Clonidine
A
- alpha 2 selective agonist (selective for alpha 2 receptors)-> alpha2»alpha1»>beta1/beta2
- agonist but behaves like antagonist (switches off noradrenaline synthesis and secretion)
7
Q
Clinical uses of Clonidine
A
- treatment of hypertension and migraine
- reduces sympathetic tone
8
Q
Isoprenaline
A
- selective beta adrenoceptor agonist (not particularly selective for beta1 or beta2)->beta1=beta2»»alpha1/alpha2
- chemically related to adrenaline (but more resistant to MAO and uptake 1)
- first agent used for asthma (good dilating agent) but now predominant use in CVS emergencies
- drives stimulation of beta1 receptors on heart to increase cardiac output as heart is failing
- CAUTION: also stimulates beta2 receptors in vascular smooth muscle resulting in vasodilation of blood vessels in skeletal muscle->causes large fall in venous blood pressure which triggers reflex tachycardia via baroreceptor stimulation to ensure sufficient blood supply reaches tissues
9
Q
Clinical uses of Isoprenaline
A
- Cardiogenic shock
- Acute heart failure
- Myocardial infarction
10
Q
Dobutamine
A
- selective beta 1 adrenoceptor agonist
- similar action to isoprenaline without beta2 receptor effect (lacks isoprenaline’s reflex tachycardia)
- predominant use in emergency medication (short 2 minute plasma half life as rapidly metabolised by COMT)
11
Q
Clinical uses of Dobutamine
A
-Treatment of cardiogenic shock
12
Q
Salbutamol
A
- Otherwise known as Ventolin (blue inhalers)
- Selective beta 2 adrenoceptor agonist->beta2»beta1»>alpha1/alpha2
- synthetic catecholamine derivative
- relative resistance to MAO and COMT
- similar to adrenaline and noradrenaline but generally more resistant to breakdown (remains in system for longer)
- once inhaled into the airways, Salbutamol binds to beta2 receptors->beta2 coupled to cAMP->cAMP activation leads to cell hyperpolarisation (potassium efflux)->results in muscle relaxation
13
Q
Clinical uses of Salbutamol
A
- Treatment of asthma (beta2-relaxation of bronchial smooth muscle, inhibition of bronchoconstrictor subtance release from mast cells)
- Treatment of threatened premature labour (beta2-relaxation of uterine smooth muscle)
14
Q
Unwanted effects of Salbutamol
A
- Reflex tachycardia
- Fine tremor in skeletal muscles
- Blood sugar dysregulation
15
Q
Noradrenaline metabolism
A
- Tyrosine from the diet (precursor molecule) converted to noradrenaline via series of enzymatic steps (last enzymatic step occurs in the vesicle itself)
- Action potential promotes exocytosis of noradrenaline
- Noradrenaline acts on alpha/beta adrenoceptors
- Noradrenaline removed from synpase by transport proteins either into nerve terminal itself or extraneuronal tissue
- Presynaptic alpha2 receptors are negative feedback receptors influencing noradrenaline synthesis and release->negative feedback mechanism whereby noradrenaline in synapse can control own noradrenaline secretion if excessive response (alpha2 receptor stimulation leads to suppressed sympathetic nervous system function)
