SNS agonists Flashcards
what do SNS agonists do and advantage over muscarinic/nicotinic drugs
mimic NA/A by stimulating adrenoreceptors side effects aren’t as bad as different subtypes target different tissues, so SNS agonists much more selective
selectivity of NA/A
NA is MORE selective for alpha 1/2 receptors than B1/2, adrenaline the opposite, although ALL adrenoreceptors activated by both
NA metabolism and control DIAGRAM
tyrosine converted into DOPA by tyr hydroxylase, then dopamine by dopamine decarbox, then NA NA enters vesicle and is released, then binds to alpha/beta receptors- HOWEVER it binds to a prejunctional receptor called alpha 2, which controls production via -ve feedback, so less NA produced
directly acting SNS agonists- drug and type
adrenaline (non-selective) phenylephrine (alpha 1) clonidine (alpha 2) dobutamine (beta 1) salbutamol (beta 2)
effect of adrenaline on anaphylaxis
anaphylaxis is due to histamine which causes: bronchoconstriction- adrenaline counteracts this (physiological antagonism) via beta 2 hypotension- histamine dilates blood vessels: adrenaline causes tachycardia via beta 1, and vasoconstriction via alpha 1 stomach cramps- SNS causes less motility of gut
other uses of adrenaline with receptor subtypes
asthma/bronchospasm- dilates airways via beta 2 cardiogenic shock (heart not contracting)- has inotropic effects via beta 1 spinal anaesthesia- maintain BP by vasoconstriction via alpha 1 local anaesthesia- keeping anaesthetic where you want it by constricting blood flow to rest of body= prolonged action via alpha 1
side effects of adrenaline and overall
secretions- reduced mucous CVS- tachycardia, hypertension, cold (due to vasoconstriction) skeletal muscle tremors little effect on CNS/gut- tends to have few side effects unless person has CVS problems
phenyephrine- selectivity and comparison to adrenaline
more selective for alpha 1 then 2, and more selective for alpha then beta similar to adrenaline, but more resistant to COMT (peripheral enzyme), not MAO (central enzyme)- thus given to peripheral tissues rather than adrenaline
uses of phenylephrine
mainly alpha so used as vasoconstriction nasal congestion due to white cells from blood infiltrating nose and causing mucous production- by vasoconstricting less infilfration occurs= decongestant mydriatic- dilates pupil (alpha mediated)
nature of clonidine
more selective for alpha 2 than alpha 1 and beta it is an agonist of alpha 2, but alpha 2 causes negative feedback OF na, so result is sympathetic ANTAGONISM
explain glaucoma
ciliary body produces aqueous humour to protect anterior part of eye- if not drained due to venous blockage, intraocular pressure builds up, which can damage optic nerve= blindness
treating glaucoma- types of receptors
ciliary body has B2, alpha 1, and alpha 2 beta 2 agonist not suitable as will cause more aqueous humour production alpha 2 suitable to prevent NA binding to beta 2= less humour production= clonidine alpha 1 suitable as causes vasconstriction= less blood goes to ciliary body
uses of clonidine
glaucoma hypertension and migraine (link between vasodilation in brain and migraine- clonidine prevents this) effects brianstem directly to reduce SNS out= eg lower BP
isoprenaline- selectivity, comparison to adrenaline and uses
selective for both beta receptors rather than alpha similar to adrenaline but more resistant to MAO used for heart issues (cardiogenic shock/MI/heart failure)- was previously used for asthma
problem with isoprenaline
beta 2 stimulation causes dilation of veins, which can lead to fall in BP- this can stimulate baroreceptors to cause a REFLEX TACHYCARDIA- not such a problem for those with heart problems, more for those with asthma
