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Applied Pharmacology > Autonomic Pharmacology > Flashcards

Autonomic Pharmacology Flashcards

0
Q

What is the sympathetic effect on blood vessels?

A

constriction by A1
dilation by B2
constriction by A2

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1
Q

What is the sympathetic effect on the heart?

A 
increased rate (chronotrophy) by B1
increased strength (inotrophy) by B1
increased conduction (dromotrophy) by B1
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2
Q

What is the effect of the sympathetic nervous system on the eye?

A

Constriction of the radial muscle by A1=midriasis

relaxation of the ciliary muscle by B= far vision

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3
Q

What is the effect of the parasympathetic nervous system on the heart?

A

Inhibition via M2 receptors

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4
Q

What is the effect of the parasympathetic nervous system on the blood vessel?

A

Generally dilation via M3 receptors

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5
Q

What is the effect of the parasympathetic nervous system on the eye?

A

Contraction of the sphincter muscle (miosis)

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6
Q

What is the structure of the sympathetic nervous system?

A

cell bodies for preganglionic fibres in the intermediolateral columns of the 1st thoracic to 3rd lumbar segments. Axons synapse at paravertebral, prevertebral and terminal sites.

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7
Q

What are the neurotransmitters for the sympathetic nervous system?

A

Ach- preganglionic
NA- postganglionic
Adrenal medulla releases adrenaline.

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8
Q

What happens as a result of sympathetic nervous system stimulation?

A
  1. midriasis
  2. positive chronotropic effect (inc. HR)
  3. positive inotropic effect (inc. force of contraction)
  4. Increased dromotropic effect (inc. speed of conduction)
  5. Vasoconstriction/vasodilation (receptor dependant) all A, B2
  6. Bronchodilation
  7. decreased GI motility
  8. Increased sphincter tone
  9. glycogenolysis
  10. gluconeogenesis
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9
Q

How is NA made, stored and destroyed?

A

Synthesised in the nerve terminal from tyrosine by tyrosine hydroxylase (tyrosine-dopa-dopamine-NA), stored in vesicles where it is released by an action potential, undergoes re-uptake by monoamine oxidase (MAO) into the neurone and enzymatic degradation by catechol-o-methyl transferase (COMT) into a non-neuronal cell.
it affects A and B receptors.

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10
Q

What are the characteristics of the receptors that NA acts on?

A

They are GPCRs, they are divided into A and B with subdivisions in each group e.g. a1 and a2, b1, b2, b3, b4.

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11
Q

What are the characteristics of the a1 receptor?

A

it is widely distributed, it couples mainly to Gq. The 2nd messenger system mainly involves activation of PLC leading to formation of IP3 and DAG. IP3= release of Ca from SR. DAG= PKC which opens Ca channels.

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12
Q

What do a1 receptors cause?

A

vasoconstriction, positive inotropic effect, prostatic smooth m contraction, urinary sphincter muscle contraction and midriasis.

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13
Q

What are the characteristics of the a2 adrenoreceptors?

A

mainly couple to Gi and Go. Inhibits andenylyl cyclase and decrease cAMP, inhibits voltage gated Ca channels and activate Ca dependant K channels. They have a negative feedback effect on NA production.

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14
Q

What are the functions of a2 receptors?

A

they are located prejunctionally and inhibit neurotransmitter release, They are also located postjunctionally andcause vasoconstriction by acting on VSM.

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15
Q

What are the characteristics of b1 receptors?

A

the couple mainly to Gs, they stimulate adenylyl cyclase which increases cAMP and this increases PKA (increases glucose etc.), these are found mainly in the heart. inc: force of contraction, conduction and impulse formation.

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16
Q

What are the characteristics of b2 receptors?

A

Mediates activity through Gs and Gi, it can stimulate and inhibit cAMP. It relaxes VSM, causes bronchodilation and stabilises mast cells.

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17
Q

What is the receptor and neurotransmitter at the pre-postganglionic synapse and the post-cell synapse in the SNS?

A

Ach:nicotinic receptor
NA:adrenoreceptor

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18
Q

What is the structure of the PNS?

A

It has a cranial and sacral outflow, it has a localised effect as the axons of the presynaptic fibres synapse in the organ, Ach is the pre and post neurotransmitter

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19
Q

How is Ach processed?

A

Its synthesis requires choline acetyltransferase.
It is degraded by acetylcholine esterase
it acts at nicotinic and muscarinic receptors.

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20
Q

What are the functions of the PNS?

A

CV system- decreased rate, force and conductivity. Vasodilation, Ach induced nitric oxide release, GI- increased motility and secretion. Contracts the detrusor, relaxes the sphincters, miosis, bronchoconstriction and resp. secretion.

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21
Q

What are the characteristics of the nicotinic receptors?

A

ligand gated ion channels, increased permeability to Na and K which depolarises the cell. There are Nn and Nm subtypes.
Nm-skeletal muscle (somatic)
Nn- ganglia

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22
Q

What are the characteristics of muscarinic receptors?

A

These are GPCRs and there are 5 subtypes,
M1- ganglia activates PLC= IP3 and DAG, M3- Smm and glandular tissue, M5-activates PLC
M2- in the heart, inhibits adenylyl cyclase and opens K channels, M2- in the CNS (above)

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23
Q

What are the receptors/neurotransmitters at the pre/post ganglionic synapse and the post/cell synapse?

A

Ach:nicotinic, Ach: muscarinic

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24
Q

What is the enteric nervous system?

A

the 3rd division of the ANS. It is intrinsic nerve plexuses of the GI tract. the cell bodies lie in intramural plexuses in the intestinal wall. the effects are caused by 5-HT which is a neuropeptide.

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25
Q

What is co-transmission?

A

transmitters released other than Ach and NA.
e.g. Non-peptides- ATP, GABA, dopamine and NO
Peptides- VIP, substance P and CGRP
e.g. ATP released from postgang symp nerve as well as NA.

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26
Q

How do drugs act on the ENS?

A

1)interfere with the synthesis of neurotransmitter e.g. hemicholinum clocks choline (dec. Ach). 2) competition for the same metabolic pathway e.g. methyldopa is a false transmitter, 3) can block re uptake e.g. cocaine block re uptake of NA, 4) can block transport and affect storage e.g. reserpine displaces NA which is destroyed by MAO, 5) may displace the neurottransmitter e.g. amphetamine releases NA, 6) may block the release of neurotransmitter e.g. botulinus toxin block Ach release, 7) can act as an agonist receptor e.g. nicotine at nicotinic receptors, 8) can act as an antagonist e.g. atropine at a muscarinic receptor, 9) can inhibit degradation e.g. inhibitors of Ach esterase- physostigmine.

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27
Q

What are the 3 classes of drug that can be used on the PNS?

A

Muscarinic agonists
Acetylcholinesterase inhibitors
muscarinic antagonists

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28
Q

What are muscarinic agonists?

A

also called parasympathomimetics, not that commonly used in practice and are made of of two groups.

1) Synthetic choline esters and Ach- ester group makes them susceptible to AchE
2) naturally occurring cholinomimetic alkaloids

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29
Q

Examples of choline ester muscarinic antagonists?

A

You cannot use Ach itself because it is too rapidly degraded by AchE.
e.g. Methacholine, bethanecol and carbachol

30
Q

What are the effects of mathacholine?

A

it is mainly muscarinic, slow degradation by AchE compared to Ach, main effect is on the CVS.

31
Q

What are the characteristics of Benthanecol and Carbachol?

A

They are resistant to AChE, they both have a GI effect-induce gastric motility.
Bethanecol is mainly muscarinic
carbachol is used to topically induce miosis and has some nicotinic action that contributes to the release of Ach from the nerve terminals

32
Q

examples of cholinomimetic alkaloids?

A

muscarine, pilocarpine, arecoline
pilocarpine- dominant muscarinic activity, induces miosis in the eye (0.5%, 1% 2%), treatment of glaucoma but not for diseases with lens luxation as it makes it more unstable.

33
Q

What are Acetylcholinesterase inhibitors?

A

they have a cholinergic effect initially but prolonged depolarisation may have the opposite effect, can act as direct agonists and antagonists. There are two categories:
reversible AchEI- physostigmine
Irreversible AchEI- organophosphates- parathion

34
Q

What contributes to the toxicity of acetylcholinesterase Inhibitors?

A

their volatility and solubility( how well they will be distributed-lipid sol) and whether they are reversible or not. e.g. sarin- nerve gasses that are lipid soluble, volatile and irreversible.

35
Q

What are the uses for Acetylcholinesterase Inhibitors?

A

mainly the eye, Skm and GI tract.

36
Q

What does Edrophonium Chloride do?

A

AchEI- short acting quaternary ammonium compound.

reverses non depolarising m relaxants, diagnostic for myasthenia gravis, rapid onset, given by slow IV

37
Q

What does Neostigmine do?

A

AchEI- moderate duration of action, reversal of non depolarising m relaxants, treatment of myasthenia gravis, orally or IV, given 3x daily and dose can be reduced.

38
Q

What does Pyridostigmine do?

A

moderate duration, treatment of myasthenia gravis, orally 2x daily (BID), half life is 4hrs or if IV 2hrs.

39
Q

What are the clinical signs of AchEI toxicity and why do they occur?

A

excess cholinergic effects- salivation, muscle tremor, defecation (stim. of GI), miosis, collapse ( due to dec. HR, vasodilation and dec. CO), Used for somatic Ach receptors but they will stimulate PNS muscarinic receptors too hence the increased activity.
Have antimuscarinic agents to hand e.g. atropine

40
Q

What are muscarinic antagonists and what is their structure? (parasympatholytics)

A

competitive antagonists for Ach at muscarinic receptors.
they have limited effects at the neuromuscular junction or in ganglionic transmission. They have a bulky aromatic group in place of the acetyl group e.g atropine.

41
Q

Examples of muscarinic antagonists?

A

Atropine, scopolamine, tropicamide, glycopyrronium, ipratopium, cyclopentolate.

42
Q

What are the characteristics of Atropine?

A

can be given i/v, i/m, s/c, p/o.
metabolised in the liver and excreted by the kidneys. It is a tertiary amine so is expected to be ionised at physiological pH but it crosses the gut, BBB and conjunctival sac. It is used as a premed to reduce salivation.

43
Q

What are some of the uses of atropine?

A

not in the horse- gastric motility is reduced and can cause central excitation.
treatment of organophosphate toxicity, dilate the pupil for examination, used to increase HR, used with AchEI to prevent side effects from musc. stimulation. anti spasmodic effect in the gut.

44
Q

What are the side effects of atropine?

A

CNS stimulation in the horse.
constipation
tachycardia
urinary retention

45
Q

What does Scopolamine do? (musc. antagonist)

A

Used for drying secretion and has antiemetic properties. Naturally occuring.

46
Q

What does Glycopyrronium Bromide do? (musc. antagonist)

A

Synthetic.
does not cross the BBB or placenta.
less CNS effects so good for caesarians, less tachycardia, used in ocular surgery to prevent vagal stimulation.

47
Q

What does Ipratopium bromide do? (musc. antagonist)

A

Bronchodilation in horses with COPD, It is inhaled as its absorption is poor- local action and few side effects.

48
Q

What does cyclopentolate do? (musc. antagonist)

A

mydriatic and cycloplegic (dilated), long duration of action.

49
Q

What does Tropicamide do? (musc. antagonist)

A

Used as a mydriatic ( not cycloplegic), for intra ocular exam, rapid acting shorter duration.

50
Q

What are the two types of receptor for nicotinic agonists and what would be given after their use?

A

Nm- skeletal muscle
Nn- in the autonomic ganglia- will affect PNS and SNS.
Give AChEI to build up ACh by preventing its breakdown.

51
Q

What are ganglionic blockers?

A

PNS and SNS Nn receptor (diffuse effects= bad) Not relevant!

52
Q

What drugs are used on somatic efferent system and how are they used?

A

Skeletal muscle nicotinic receptor agonists (Nm).
They are used to relax skeletal muscle. On recovery an AChEI should be given to allow ACh to build up and combat the effects of the drug on PNS and ANS nicotinic receptors (Nn), a muscarinic antagonist should also be given to block ACh on the PNS muscarinic receptor.

53
Q

What are the drugs used on the SNS and the ligands?

A

alpha agonists and antagonists (selective and non selective)
beta agonists and antagonists.
Endogenous- NA, A and dopamine

54
Q

What are the characteristics of a non-selective agonist in the SNS and what are they used for?

A

e.g. Adrenaline (IV)
acts at alpha and beta adrenoreceptors. increases heart rate and force of contraction, induces vasoconstriction. Used for cardiac arrest and anaphylaxis. They undergo re-uptake (MAO) and are metabolised by non neuronal tissue (COMT).

55
Q

What is isoprenaline and what are its effects?

A

non selective beta adrenergic agonist. Metabolised by COMT in the liver.
positive inotropic and chronotropic effects. can induce arrythmmias and myocardial necrosis.

56
Q

What are the characteristics of dopamine and what is it used for?

A

It is a neurotransmitter with five subtypes (D1-D5). It induces a vasodilation (D1) by increasing intracellular cAMP. Prevention and management of acute renal failure in low doses. But in high doses it can induce vasoconstriction through alpha1 adrenoreceptors.

57
Q

What are the characteristics of Phenylpropanolamine?

A

It is an alpha-agonist used to treat urinary incontinence in the bitch (targets internal sphincter and inc. tone) . Given orally and also used as a nasal decongestant . It has tyramine like activity and induces release of NA.

58
Q

What do the beta 1 agonists do?

A

They have mainly cardiac effects and will increase heart rate and force of contraction.

59
Q

What are the characteristics of Dobutamine?

A

It is a synthetic beta 1 agonist used in equine anaesthesia to maintain a mean arterial pressure in excess of 70mmHg. (Skm myopathy), it is used in cardiac crisis for inotropic support, Give IV as short t1/2.

60
Q

What are the characteristics of beta 2 agonists?

A

They induce Bronchodilation and uterine relaxation, they have been used as growth promoters.

61
Q

What are the characteristics of Clenbuterol?

A

It is a beta 2 agonist that is used to treat RAO in horses, it can be given IV or orally. It can induce vasodilation and tachycardia.
It promotes growth by repartitioning the ratio of fat to lean muscle- hypertrophy in m cells and lipolysis.

62
Q

What are the characteristics of Terbutaline?

A

It is a beta 2 agonist that is used as a bronchodilator- it has increased cardiac side effects. It is an alternative to propantheline (musc. antagonist) in conduction disturbances (conduction block)- admin orally.

63
Q

What are the characteristics of Isoxuprine?

A

It is a beta 2 agonist used to treat navicular disease as it induces vasodilation. It is also used as a tocolytic drug (reduce uterine contractions and delay parturition)- good for c-section or embryotomy- reverse by oxytocin.

64
Q

What are the characteristics of the alpha 1 adrenorecptor agonists and give some examples?

A

Induce vasoconstriction and increase the force of myocardial contraction.
e.g. Phenylephrine (induce mydriasis) and methoxamine.

65
Q

What are the characteristics of the alpha 2 adrenoreceptor agonists and give some examples?

A

Central sedative effects. e.g. clonidine (diagnosis of GH deficiency-it stimulates GHRF), xylazine, metomidine and detomidine.

66
Q

What are the characteristics of the alpha 1 antagonists and give some examples?

A

They cause vasodilation.

e.g. prazoin, terazosin and alfuzasin.

67
Q

What are the characteristics of Phenoxybenzamine?

A

Irreversible alpha 1 antagonist- it blocks the a1 receptor. It has been used to treat laminits to induce vasodilation and urinary retention by causing relaxation of the internal sphincter. It can induce hpotension.

68
Q

WHat type of tumour can phenoxybenzamine be used to treat?

A

Phaeochromocytoma in the adrenal medulla. It causes excessive secretion of adrenaline= hypotensive and tachycardic. It stabilises the pulsatile release of adrenaline so it is good that it is irreversible!

69
Q

What are the characteristics of Prazosin?

A

It is an a1 antagonist that is used to treat urinary tract conditions by relaxing the internal sphincter and contracting the detrusor m. NB- a musc agonist must be given or the detrusor m will contract on a closed sphincter.

70
Q

What are the a2 antagonists used for and give some examples?

A

To reverse sedation caused by the a2 agonists. e.g. yohimbine and atipamezole

71
Q

What are the characteristics of the beta antagonists?

A

Called ‘beta blockers’- They antagonise the effect of the b1 and NA in the heart so they lower HR, hypertension and force of contraction.

72
Q

What is Timolol used for?

A

It is a beta blocker than is used for the treatment of glaucoma. It reduces the production of aqueous humour and widens the drainage angle by constricting the pupil.

Applied Pharmacology (5 decks)

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