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SNS antagonists Flashcards

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1
Q

where are alpha 2 receptors located?

A

presynaptic terminals

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2
Q

what effect do alpha 2 receptors have?

A

negative feedback on NA release

these can be targetted

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3
Q

normal alpha 1 function

A

vasoconstriction

relaxation of GIT

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4
Q

normal alpha 2 function

A

inhibition of NA release
contraction of VSMC
CNS

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5
Q

normal beta 1 function

A

cardiac stimulation
relaxation of GIT
renin release

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6
Q

normal beta 2 function

A

bronchodilation
vasodilation
relaxation of VSMC
hepatic glycogenolysis

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7
Q

normal beta 3 function

A

lipolysis

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8
Q

non selective antagonist example (alpha and beta)

A

carvediol

labetalol

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9
Q

non selective alpha antagonist

A

phentolamine

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10
Q

alpha 1 selective antagonist

A

prazosin

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11
Q

non selective beta antagonist

A

propanolol

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12
Q

beta 1 selective antagonist

A

atenolol

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13
Q

what are the main elements that need to be controlled to treat hypertension

A

blood volume
cardiac output
TPR

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14
Q

what tissues are targeted by anti-hypertensives?

A
  • kidney (renin) beta 1
  • heart beta 1
  • arterioles (TRP determinant) alpha 1/2
  • SNS nerves (vasoconstrictor molecule release e.g. NA) beta 1/2
  • CNS (BP set point, system regulation in BP control) beta 1/2
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15
Q

beta blocker suffix

A

-olol

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16
Q

what is used to treat hypertension

A

beta blockers
targeting the heart (beta 1)
kidney (beta 1) and CNS

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17
Q

effect of beta blockers on the heart

A

Beta 1
reduce inotropic and chronotropic effect
(this effect disappears in chronic treatment)

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18
Q

effect of beta blockers on kidney

A

beta 1

reduced renin production

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19
Q

effect of beta blockers on CNS

A

beta 1 and 2

reduce sympathetic tone

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20
Q

beta 1 blockade

A

beta 1 is also located on pre-synaptic membrane
when bound, it reduces positive feedback on NA release
this has anti-hypertensive effects

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21
Q

unwanted effects of beta blockers/antagonists

A

o Bronchoconstriction – patient has an airway disease e.g. asthmatics
o Cardiac failure – in patients with heart disease sympathetic drive is required
o Hypoglycaemia - beta blockers may mask symptoms (tremors etc.) and non-selective beta blockers will also block hepatic glycogenolysis (beta 2).
o Fatigue – reduced CO and muscular perfusion
o Cold extremities – loss of beta-receptor mediated vasodilation.
o Bad dreams- CNS

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22
Q

non selective beta blocker

A

propanolol

has equal affinities for beta 1 and 2, therefore can have adverse effects
causes little effect at rest
during exercise it reduced HR, CO and BP

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23
Q

cardiac selective beta blocker

A

atenolol

beta 1 selective
antagonises the effects of NA on the heart but affects organs with beta 1 like kidneys

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24
Q

atenolol vs propanolol

A

atenolol (beta 1 selective) is less selective for beta 2, so is less likely to give asthmatic patients an issue compared to non selective propranolol but is not entirely safe

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25
change in atenolol selectivity
with higher concentrations, the drug becomes non-selective
26
labetalol and carvediol (mixed)
``` alpha 1 and beta 1 more for beta 1 than alpha 1 vasodilator effect lowers BP via TRP reduction therefore decreased HR or CO effect wanes with chronic use ```
27
what is the problem with using alpha antagonists?
postural hypotension arterioles are affected, decreasing the TPR this leads to reflexive tachycardia therefore increased HR and CO (beta mediated)
28
phentolamine
non selective alpha antagonist causes vasodilation fall in BP
29
how does phentolamine enhance reflexive tachycardia?
they bind to alpha 2 receptors presynaptically | blocking the inhibition of NA
30
When is phentolamine mainly used?
treating phaechromocytoma induced hypertension increased GIT motility, therefore diarrhoea
31
prazosin
alpha 1 selective causes vasodilation by inhibiting the vasoconstrictor activity of NA fall in BP and CO also decreased LDL and increases HDL (good effect)
32
phentolamine vs prazosin
prazosin causes less reflexive tachycardia as it does not bind to alpha 2, so NA release can be inhibited. phentolamine is non-selective and will bind to alpha 2 too.
33
example of false transmitter prodrug
methyldopa
34
what is the false transmitter that methyldopa produced
once taken up by noradrenergic neurones, decarboxylated and hydroxylated, it becomes alpha methyl noradrenaline
35
alpha methyl NA activity
less affinity/active to alpha 1 than NA more affinity/active to presynpatic alpha 2 than NA therefore less vasoconstriction and more inhibition of NA release
36
why is alpha methyl NA good at its job
it is not degraded by MAO-O so it accumulates in the synaptic cleft in larger quantities than NA, so it displaces NA from the vesicles
37
clinical use of methydopa
renal disease cerebrovascular disease [helps maintain blood flow to these regions] hypertension, e.g. in pregnant women as it has no adverse effects despite crossing the placenta
38
adverse effects of methyldopa
``` dry mouth (reduced salivations) sedation orthostatic hypotension male sexual dysfunction ```
39
what is an arrhythmia?
abnormal or irregular heart beat mainly caused by myocardial ischaemia
40
why do SNS antagonists need to be used to treat arrhythmias?
SNS activity exacerbates arrhythmia via beta 1, especially after ischaemia AV conductance depends on SNS activity
41
what drug is usually used to treat arrhythmias?
propanolol (non selective beta antagonist, class II) - reduced mortality of patients with myocardial ischemia - works particularly well in cases that occur during exercise or mental stress
42
what is angina?
chest pain due to insufficient O2 supply to myocardium, so it is unable to meet its demands
43
referred pain of angina
spreads down dermatome T1 in the chest, arm and neck | brought on by exertion of excitement
44
types of angina
stable unstable variable
45
stable angina
fine at rest, pain on exertion due to fixed narrowing of coronary vessels
46
unstable angina
pain with less exertion and at rest | thrombus without the complete occlusion of the vessel
47
variable angina
at rest, caused by coronary artery spasm , associated with atheromatous disease
48
what are the 3 ways beta blockers ease angina?
reduce myocardial demand by: - decrease inotropic effect (contractility) - decrease chronotropic effect (heart rate) - decrease systolic pressure at low effects does not affect bronchial smooth muscle
49
adverse effects of beta adrenoreceptor antagonist
``` fatigue insomnia dizziness sexual dysfunction bronchospasm bradycardia heart block hypotension ``` therefore not used in patients where this can be exacerbated e..g congestive heart failure
50
what is glaucoma?
an increase in intraocular pressure due to the poor drainage of aqueous humour can permanently damage the optic nerve
51
how is aqueous humour produced?
by blood vessels in the ciliary body uses carbonic anhydrase indirectly related to BP (fluid leakage used)
52
what is the flow pathway of aqueous humour?
``` ciliary body posterior chamber pupil anterior chamber trabecular meshwork into veins and canal of Schlemm ```
53
examples of beta adr. antagonists used in glaucoma treatment
carteolol hydrochloride levobunolol hydrochloride timolol maleate non selective of beta 1 and 2 betaxolol hydrochloride is beta 1 selective
54
what is the effect of glaucoma medication?
reduce the rate of which aqueous humour is produced by blocking Beta-1 and stimulating alpha 2 on the ciliary body
55
what effect does beta 1 blockade have?
vasodilation and fall in total peripheral resistance and BP antagonises noradrenaline on the heart also effects on kidney
56
what are the main mediators of peripheral resistance?
alpha 1 receptors therefore alpha blockade causes rapid fall in arterial pressure
57
how does non-selective alpha antagonism lead to drop in peripheral resistance and therefore BP?
- subcutaneous vasodilation | - increased flow through cutaneous and splanchnic vascular beds
58
which cells of the adrenal medulla is impacted by phaechromocytoma?
chromaffin cells
59
what is phentolamine used for?
phaechromocytoma induced hypertension
60
what is the negative consequence of using a non selective alpha antagonist like phentolamine?
- can bind to alpha 2 - less inhibition of NA release - enhanced reflex tachycardia
61
what is the benefit of using an alpha 1 selective antagonist over a non-selective alpha antagonist?
e.g. prazosin over phentolamine less reflex tachycardia as there is no alpha 2 blockade
62
what is the main effect of methyldopa?
as a false transmitter it is most active on pre-synaptic alpha 2 auto-inhibitor of NA release stimulates vasopressor centre in brainstem--> reduced sympathetic outflow
63
what aggravates arrhythmia?
increases sympathetic drive to the heart via beta 1 particularly after MI where there is an increase in sympathetic tone
64
what does AV conductance depend on ?
sympathetic activity via beta 1
65
what effect do beta antagonists have on the refractory period?
increases the refractory period to slow ventricular rate by interfering with AV conductance
66
what effect do beta antagonists have in glaucoma?
reduces aqueous humour production
67
how is aqueous humour production indirectly linked to blood pressure?
increased blood flow to ciliary body means more production of aqueous humour

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