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Lecture 10: Sympathetic NS Flashcards

1
Q

How does NE effect the CV system?

A
  • overall vasoconstriction (increase in TPR)
  • increased strength of vasoconstriction (ionotropy)
  • initially HR goes up (chronotropy) but drops back down due to baroreceptor reflex
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2
Q

What would be used to delay premature contractions?

A

epinephrine: decreases smooth muscle tone so it can’t contract as well

salbutamol: B2 agonist that relaxes uterine smooth muscle

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3
Q

Phenylephrine (PE), an a1 Ag are used in cold remedies because?

A
  • during colds, there is vasodilation causing fluids to lead causing congestion
  • a1 agonist causes vasoconstriction in upper respiratory mucosa to stop congestion
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4
Q

Phenylepherine (half life and potency)

A
  • selective a1 agonist
  • longer t1/2 than NE because not broken down by COMT, but less potent than NE
  • can activate B2 R at high doses
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5
Q

Phenylepherine clinical use

A

selective a1 agonist

CV: increases BP
- causes reflex bradycardia, so used to treat atrial bradycardia
- in hypotensive states (people who are hypertensive should not use this)

decongestant and anti-allergy
- causes constriction
- but desensitization with repeated dosing

dilation (myadratic)

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6
Q

clonidine use

A

selective a2 R agonist (mainly on N terminals)

treats hypertension
- decreases BP, bradycardia, and CO due to blocking NE release from nerve terminals
- centrally blocks excitatory outflow
- peripherally presynaptic inhibition

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7
Q

clonidine ADR

A

adverse effects
- decreased TPR with chronic admin
- rebound hypertensive crisis with sudden withdrawal
- dry mouth and constipation (targets a2 on parasympaethic terminals too), bradycardia,
and sedation

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8
Q

Apraclonidine

A

more seletive than clonidine

use as adjust glaucoma treatment because it is very local (reduces production of aqueous humour and decreasing IOP)

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9
Q

Isoproterenol

A

non-selective B agonist
- no therapeutic use
- most potent B agonist with longer t1/2
- severe cardiac side effects: peripheral vasodilation, tachycardia, myocardial stimulation

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10
Q

Dobutamine

A

selective B1 agonist
- synthetic DA derivative
- positive ionotropic effect greater than chronotropic effect
- increases SV at low dose and no change in HR –> increases CO
- used short term treatment of HF, acute MI, and heart surgery (long term would cause death)

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11
Q

What are selective B2 R agonists used to treat?

A

primarily asthma without stimulating B1

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12
Q

Salbutamol (albuterol)

A

selective B2 R agonist

bronchodilation
- B2 on bronchiole sm
- skeletal muscle vasodilation to decrease TPR
- high dose could stimulate CV effects

delay premature labour
- relaxes uterus sm so there are no contractions

duration and t1/2 can be extended with newer agents

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13
Q

Salmeterol

A

selective B2 agonist
- anchors to R for extended action

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14
Q

Terbutaline

A

selective B2 agonist

used to delay premature labour

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15
Q

Mirabegron

A

selective B3 agonist
- treats overactive bladder

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16
Q

Indirect acting sympathomimetics can act by

A
  • increase synthesis
  • stimulate release
  • inhibit presynaptic transporter for reuptake to increase NT in cleft –> cocaine (DAT), desimimpramine/amytriptyline (NET), amphetamine
  • inhibit degredation by enzymes –> MAO-A I: clorgyline, MAO-B I: selegiline
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17
Q

Why should we be cautious when eating foods with tyramine (cheese)?

A
  • VMAT substrate with no direct effect
  • when used with MAOIs –> this prevents degrdation and increases NE displacement causing a sudden increase in BP
  • can lead to hypertensive crisis
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18
Q

Ephedrine

A

mixed action sympathomimetic
- both NE release and direct a1, B1, B2 R binding
- orally effective prolonged action stimulant
- increases heart rate, bronchodilation and skeletal muscle tone
- less potent vasopressor than EPI

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19
Q

Pseudoephedrine

A

mixed action sympathomimetic
- isomer of ephedrine
- a1, b2 R agonist
- decongestant, stimulant
- however can be used to make methamphetamine

20
Q

Phenoxybenzamine

A

non selective a R ANT (at a2 will block synaptic feedback –> increase NT release)
- irreversible (dose response curve shifts right)
- decreasing but persistant block 3 days after exposure

results
CV: decreases TPR, DR, and causes tachycardia (baroreceptores aren’t active so NE release into the heart increases HR)
- hypotensive response greater in HT patients
- used to treat pheochromocytoma

metabolic
- insulin secretion (unmasking B2 effects and no alpha inhibition of insulin release –> hypoglycemia), lipolysis

21
Q

Phentolamine

A

non selective alpha R ANT

  • reversible and competitive inhibition
  • slightly higher affinity for a1 –> increases SP but also triggers baro reflex and blocks a2 autoreceptors
  • cv effects same as phenoxybenzamine but transient

use
- short term HT treatment
- pheochromocytoma
- tyramine rich diets in pateinst atking MAOI

22
Q

Prazosin

A

selective a1 R ANT

used for mild-moderate HT, CHF

  • decrease in TPR, DP, VR, pre and after load, pulmonary congestion
  • increase in CO
  • tachycardia via baroR can occur –> decrease in TPR increases symp. outflow to heart but is not due to autoinhibition via a2 (bc this is a1 selective)
  • first dose phenomenon - orthostatic hypotension
23
Q

Tamsulosin

A

selective alpha 1 R ANT

used to treat
- mild/moderate HT and benign prostatic hyperplasia (BPH - a1A overexpression)
- high affinity for a1A and a1D subtypes (70% alpha R are a1A in prostate and sphincter of bladder)

24
Q

Yohimbine

A

selective a2 ANT
(not used because it inhibits autoreceptors)

low dose: reversible competitive a2 ANT
- stimulates NE release
- increases BP, HR, tremor, excitation, ADH release
- blocks clonidine peripheral CV/motor effects

high doses: blocks a1 R
- causes transient decrease in BP and binds to 5HT R

used to be for treating male sexual dysfunction but rplaced by PDE inhibitors

25
Nadolol
non selective B R ANT - longest acting: t1/2 = 14-24 hours - slow absorption - used as prophylaxis for angina
26
Pindolol
non selective B R ANT - acts as partial agonist --> in the absence of catecholamines it maintains signalling but in excess it will block beta R - can be used in bradycardia or low cardiac reserve
27
Timolol
non selective beta R antagonist - similar t1/2 as propranolol (4 hours) but less potent - clinical use in glaucoma to decrease IOP
28
Propranolol
non selecting beta R antagonist absorbed from GI, t1/2 =4 hours CV therapeutic effects - negative chronotropic effects = bradycardia (HT or normotesnive during exercise) - negative ionotropic effect, decreased CO, decreased O2 use, decreased ACE - unbalanced vagal tone: slowed pacemaker activity, decreased AV conduction - increased TPR via alpha R activation but overall hypotension with chronic use
29
Propranolol effects in a normotensive individual
- efficacy depends on sympathetic tone --> won't do anything to a normal person btut will have an effect on someone who is hypernsive since they have a lot of NE
30
Propranolol unwanted effects
bronchiolar smooth muscle - bronchospasm and airway resistance increased due to block of B2 - not ideal for asthma metabolic effects - inhibit insulin secretion via B2 block - block hyperglycemic response to EPI --> alpha2 activity increases blood glucose --> can induce hypoglycemia after exercise or insulin admin if there are no glucagon stores - can mask hypoglycemic symptoms such as increase in HR so people don't know they're hypoglycemic - need to be used with caution in diabetics predictable, widespread, and diffuse effects - severe bradycardia, CHF, bronchoconstriction - hypoglycemia - aggravation of peripheral artery disease (PAD) due to unopposed alpha R activation CV effects - with abrupt withdrawal
31
Metoprolol/Atenolol
selective B1 R ANT (cardioselective) - similar activity as propranolol at B1 but less at B2 - prophylaxis of angina, HT, heart failure
32
Esmolol
selective B1 R Antagonist short acting - rapidly hydrolyzed by esterases in blood cells
33
Betaxolol
used to treat glaucoma - opthalmic prep alone or with muscarinic (pilocarpine) to decrease IOP
34
Labetolol
mixed action beta ANT (3rd gen) ANT at B1 and a1 (3:1 ratio of antagonist) partial AG at B2 - won't block diastolic pressure drop so won't cause reflexive tachycardia decrease in BP without reflex tachycardia and increase in CO
35
Carvedilol
mixed action beta antagonist ANT at a1 and B with 10x higher affinity for B - reduce TPR and improve LV ejection fraction
36
Cimetidine interaction with beta blockers
CIMETIDINE (antihistamine) inhibits CYP associated with metabolism of PROPRANOLOL, METOPROLOL, LABETALOL - increases their bioavailability and plasma concentration
37
What is the effect of Beta Adr R ANT on insulin effects?
insulin hypoglycemic effects enhanced/prolonged can mask hypoglycemia
38
Beta blocker paradoxical pharmacology in CHF and asthma
1. congestive heart failure Beta R agonist - acute: beneficial (increases contractility) - chronic: detrimental Beta R antagonist - acute: detrimental (decreases contractility_ - chronic: beneficial (increases contractility and decreases mortality) 2. asthma Beta R AG - acute: beneficial (bronchodilation) - chronic: detrimental Beta R ANT - acute: detrimental (bronchoconstriction) - chronic: ALSO DETRIMENTAL
39
Reserpine MOA
indierect ADR ANT binds to VMAT --> blocks transport of NE/DA into vesicles --> NE leaks into cytoplasm and is degraded by MAO --> decreases abilty to store NE so there is no NT release when an action potential happens chronic treatment - R upregulation - increases sensitivity to catecholamines --> sympathomimemtic effects - abolishes response to indirect acting sympathomimetics used for Ht with hydrocholothiazide
40
Reserpine clinical CV effects and ADR
CV effects - decreased NE in peripheral synaptic terminals --> decreases stimulation of a1 R --> decreased S tone and PS is dominant tone - decreased HR, BP, CO - effects additive with hypertensive agents Adverse effects PS tone dominant - bradycardia, postural hypotension - NA and fluid retention - increased GI tone and decreased --> increased motility and diarrhea - increased nasal congestion and respiratory issues CNS - Parkinsonism, lethargy,s edation, depression - increse breast gancer, galatorrhea
41
effects of reserpine on tyramine and amphetamine
reduces their effects - tyramine: precursor to catecholamines --> res leads to their degredation - amphetamine: increased DA/NE in synapse --> res prevents them from being released into the synapse
42
Guanethidine
indirectly acting ADR ANT - competes for NAT with NE --> transported into peripheral nerve endings and accumulated in vesicles - gradual depletion of NR from vesicle stores - chronic use leads to supersensitivity and potebtiates exogenous NE and sensitizes effector cells to catecholamines - effects of indirect sympathomimetics are reduced - blocks amine uptake and vesicle NE release after MOA degredation false transmitter --> cocaine, TCAs interefere competitively with uptake of guanethidine
43
alpha-methyldopa/alpha-methyl NE
indirectly acting ADR ANT - false transmitter - substrate for dopa decarboxylase in vesicles - released upon nerve stimulation
44
alpha-methyltyrosine
indirectly acting ADR ANT - inhibits biosynthesis of catecholamines centrally, periphearally, and in adrenal medulla - competitive inhibitor of tyrosine hydroxylase clinical CV effects - decreased HR and BP - greater response in hyperstention: decreased TPR and CO - reduced SYMP tone
45
Clonidine's indirect ADR ANT action
- both sympathomimemtic and sympatholytic - binds to a2 autoreceptor and inhibits NE release - in medulla oblongata: blunts sympathetic tone - peripherally: decreases NE release form axon terminal use - prophylactic for migraine - alleviate alcohol and opioid withdrawal ADR - dry mouth, constipatoin, sedation, bradycardia - rebound HT with sudden withdrawal - TCA, desmethylimipramine, phenothiziane interfers with CV anti hypertensive effects

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