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Ocular Pharmacology > Week 3 > Flashcards

Week 3 Flashcards

1
Q

What is a Ligand - Gated Ion channel receptor and where is it located?

A

Ligand is an ion or molecule that forms a complex with other biomolecules to induce a biological response. It binds to a receptor to open or close an ion channel, which results in a cellular response.

On the cell membrane

e.g. Nicotonic ACh receptor

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2
Q

What is a G - protein coupled receptor?

A

Drug attaches to receptor which either activates or inhibits G – protein, which either directly affects an ion channel or affect other secondary chemical messengers (e.g., cyclic adenosine monophosphate (cAMP) to cause a cascade) Example: beta – adrenergic receptors (adrenaline)

On the cell membrane

e.g. Muscarinic ACh receptor

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3
Q

What is Kinase - linked receptor?

A

Receptor is stimulated by a drug on the extracellular side, which activate an enzyme cascade within the cell. Involves tyrosine kinase (protein synthesis). Mediate action of growth factors, cytokine, and hormones.

On the cell membrane

E.g. cytokine receptors

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4
Q

What is a nuclear receptor?

A

Regulate DNA transcription. A lipophilic ligand crosses cell membrane, binds to intracellular receptor, translocates into nucleus to regulate gene transcription that sets of a cellular response. (e.g., corticosteroids)

Within the cell

E.g. oestrogen

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5
Q

What is a false substrate?

A

get transformed into a chemical by an enzyme and replaces a naturally occurring chemical and alters normal function of the cell

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6
Q

What is the function of the sympathetic system?

A

fight or flight. Cell body in the pre – or para – vertebral ganglia. (Increase in HR, dilated pupil, bronchiole dilate, reduces gut motility) Controlled by the hypothalamus.

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7
Q

Describe the 3 orders of the sympathetic system

A

1st order – central ganglion goes from the hypothalamus, down the spine to ciliospinal centre of budge
2nd order – Preganglionic neuron leaves the ciliospinal centre of budge, exits the spinal cord near T1 – T3 through the ventral root, passes near the apex of the lung and subclavian artery before ascending the sympathetic chain to synapse at the superior cervical ganglion (level C3 – C4, near common carotid artery bifurcation)
3rd order: Postganglionic neuron levels the superior cervical ganglion following the internal carotid artery and ophthalmic division of CN 5:
a) Goes via nasociliary nerves, to the short and long ciliary nerves to innervates the iris dilator muscle
b) Some of the nerves go to the tarsal muscles (superior is called Mullers muscle)

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8
Q

Receptor and Action on the sympathetic Spinchter muscle

A

α β
Pupil dilation (relaxation – only a small effect)

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9
Q

Receptor and Action on the sympathetic dilator muscle

A

α1 (main) - Pupil dilation (contraction)
α2 - Pupil miosis (relaxation)

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10
Q

Receptor and Action on the sympathetic ciliary muscle

A

β1, β2 (main) - Relax accommodation
Secretion of aqueous humor
Inhibit transmitter release

α1 (some) - less aqueous humour
α2

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11
Q

Receptor and Action on the sympathetic Muller’s muscle

A

α2 (main) - Widening of palpebral aperture

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12
Q

Receptor and Action on the sympathetic blood vessels

A

α1 and α2 - Constriction of blood vessel

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13
Q

Receptor and Action on the sympathetic trabecular meshwork

A

β2 - Increase outflow of aqueous humour

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14
Q

Location of Alpha 1 receptors

A

Contraction of smooth muscle in blood vessels, dilator muscle, intestinal sphincters

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15
Q

Location of Beta 1 receptors

A

Predominantly in heart and adipose tissue (comprises of only 10% of beta – adrenergic receptors in the iris – ciliary body)

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16
Q

Location of Beta 2 receptors

A

In the lungs, liver and vascular smooth muscle

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17
Q

Location of Beta 3 receptors

A

Induce breakdown of fat cells (not clinically relevant to eye)

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18
Q

What are the ocular effects of adrenergic agonist (alpha receptor)?

A
  • Causes Muller’s muscle to contract
  • Vasoconstriction of blood vessels
  • Pupillary dilation and reduction in IOP
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19
Q

What are the ocular effects of adrenergic agonist (alpha 1)?

A

Beta receptor:
- Mild relaxation of ciliary muscle activity
- Pupillary dilation (small effect)

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20
Q

What is an example of adrenergic agonist?

A

Example: Phenylephrine
Causes: pupillary dilation (stimulating dilator muscle) and vasoconstriction of blood vessel. Does not affect ciliary muscle and accommodation. 2.5% used to distinguish between episcleritis and scleritis, diagnose Horner’s syndrome.

21
Q

What are the effect of adrenergic [alpha - 2/non selective]

A

Alpha receptor
- Causes Muller’s muscle to contract
- Vasoconstriction of blood vessels
- Pupillary dilation and reduction in IOP

22
Q

Facts about Apraclonidine (alpha 2 agonist)

A

(weak affinity for a1 – sometimes considered as a non – specific alpha agonist). Used for short term IOP reduction and Horner’s Syndrome

23
Q

What are the effect of adrenergic [beta] agonist?

A

Beta receptor
- Mild relaxation of the ciliary muscle activity
- Pupillary dilation (small effect)
- less effective than alpha agonists
Increased risk of systemic effect: Increase HR and broncodilation

24
Q

Facts about Brimonidine

A

Brimonidine (1000x more selective for a2 compared to a1) – used to reduce IOP by constricting blood vessels in the ciliary body and stimulating release of prostaglandins, which relaxes the ciliary muscle and increases uveoscleral outflow. A2 can cause miosis.

25
Q

What are the effects of a non - specific adrenergic agonist?

A

Increase uveoscleral outflow leading to reducing in IOP. Effects are based on which receptors are bound and the dosage. Effects can be contradictory due to activation of alpha and beta receptors

26
Q

What are the effects of Indirect adrenergic agonists?

A

(e.g., hydroxy amphetamine): Stimulates the release of norepinephrine from post ganglionic adrenergic nerves, which stimulate both alpha- and beta-adrenergic receptors. Little effect on accommodation, refractive status or IOP. Used in Horner’s

27
Q

What systemic effects do Adrenergic antagonists?

A
  • Selective for alpha or beta receptors
  • Reduce blood pressure (α1, β)
  • Reduce tumour growth (α2)
  • Slows heart rate, increases cardiac output (β1)
28
Q

What are the systemic contraindications of Alpha blockers?

A

Alpha Blockers: Hypersensitivity to alpha – blockers. Not to be used long term. Caution in elderly patients during cataract surgery as it may induce sudden iris prolapse and pupil constriction.

29
Q

What are the systemic contraindications for Non - select alpha - adrenergic antagonist?

A

Contraindicated for breast feeding mothers. Caution with px with renal impairment, stroke, coronary artery disease or current respiratory infection

30
Q

What are the systemic contraindications for Beta blockers ?

A

Beta Blockers: Asthmatic patients (b1 selective blocker could be considered as they do not affect the lungs). Px with Acute or chronic bradycardia, Avoid: Raynaud Phenomenon

31
Q

What are the ocular effects of alpha - adrenergic antagonist?

A
  • Acts on the alpha receptors
  • Thymoxamine – blocks α1 receptors by competing with noradrenaline
  • Dapirazole – block α1 receptors on dilator muscle and α2 receptors
  • Both do not produce action on ciliary muscle or change anterior chamber depth but can be used in reverse mydriasis (not available for optometrists)
32
Q

What are the ocular effect of beta - adrenergic antagonists?

A

Common for lowering IOPs

33
Q

What are the ocular effect of timolol?

A

Timolol (non-selective beta antagonist)
- Used as a common open angle glaucoma meds, likely to decrease secretion of aqueous humour
- Oral form used for blood pressure
- Caution: hypotension, bradycardia and can cause bronchial spasm in asthmatics

34
Q

Facts about Betaxolol

A

Betaxolol (competitive β, antagonist)
- Used for hypertension and glaucoma
- Competitively blocks β2 receptors: may be dose related
- Caution with respiratory illness.

34
Q

Facts about Betaxolol

A

Betaxolol (competitive β, antagonist)
- Used for hypertension and glaucoma
- Competitively blocks β2 receptors: may be dose related
- Caution with respiratory illness.

35
Q

What are synomyms for the sympathetic system?

A

Sympathetic Synonyms: Adrenergic agonist, sympathomimetic, adrenergic antagonist, Sympatholytic

36
Q

What are sysnomyns for the parasystemic system?

A

Cholinergic agonist, Muscarinic agonist, parasympathomimetic, Cholinergic antagonist, antimuscarinic, parasympatholytic

37
Q

What is the parasympathetic system?

A

rest and digest, cell body in target issue (Edinger Westfeld Nucleus)
(Decrease HR, hypertension, secretion of digestive chemicals, more sweat, pupil constriction, accommodation of the eyes)

38
Q

What is the pathway for Parasympathetic system?

A

Iris and Ciliary Muscle
1. Originates from the dorsal midbrain – both sides innervate Edinger Westphal nucleus
2. Pre – ganglionic nerve fibre travel with CN 3 and synapse in the ciliary ganglion
3. Postganglionic nerve fibre travels from ciliary ganglion via short ciliary nerves to the pupillary sphincter and ciliary body
Notes: activate the near triad – convergence, pupil constriction and accommodation

39
Q

Review the parasympathetic receptors and their actions

A

Page 23

40
Q

Effects of Parasympathetic [muscarinic] agonist systemic

A

Action of muscarinic agonists
- Decrease heart rate, contraction force, conduction velocity and hypotension
- Bladder smooth muscle and bronchioles constrict
- Increased gut motility, dilation of sphincter and secretion of digestive chemicals and increased sweating
- DUMBBELSS (diarrhea, urination, miosis, bronchospasm, bradycardia, excitation of skeletal muscle and CNS

Contraindications
- Coronary vascular disease (narrow vessels that have decreased blood flow gets worse after taking a muscarinic agonist, as the heart contracts less)
- Asthma, or chronic obstructive pulmonary disease
- Peptic ulcer
- Hyperthyroidism

41
Q

Effects of muscarinic agonist (Ocular)

A
  • Results in pupil miosis/constriction (M3)
  • Ciliary body contraction/accommodative spasm (M3)
  • Transient myopia in young people
  • Not advisable for pre – presbyopes
  • Reduces IOP
42
Q

Effects of Pilocarpine

A

Acts on M1 – M3 and M4 partially. Induces miosis or IOP lowering via ciliary muscle constriction. Not very effect at reversing dilation. Side effects include headaches and nausea due to ciliary body spasm

43
Q

Effects of indirect muscarinic agonist

A

For treating myasthenia gravis (e.g., pyridostigmine and neostigmine) works by blocking acetylcholine esterase so more acetylcholine to work on the muscarinic receptors. During cataract surgery, Carbachol is used for pupil constriction.

44
Q

Effects of parasympathetic [muscarinic] antagonists (systemic) (actions)

A
  • Inhibit of secretions
  • Bradycardia (low dose)
  • GI tract inhibition
  • Bronchial relaxation
  • Central nervous system excitation
45
Q

Effects of parasympathetic [muscarinic] antagonists (systemic) - Contraindications

A
  • Acute asthma
  • Myocardial infarction
  • Hyperthyroidism
  • Urinary retention
  • Narrow – angle glaucoma
  • Myasthenia gravis
46
Q

What toxic reaction do you need to watch out for with parasympathetic antagonists?

A

Hot as a hare, red as a beet, dry as a bone, blind as a bat, mad as a hatter

Dry: blocking of sweat glands, exocrine glands (dry mouth, skin and sore throat)
Hot and red: thermal regulation, increases heart rate, blook goes to skin
Blind: dilated pupils, paralysis of accommodation
Mad: Blocked M1, 4 and 5 receptors in CNS causes excitation that is seen as confusion and disorientation

47
Q

Effects of muscarinic antagonists (ocular)

A
  • Pupil dilation
  • Paralysis of accommodation
  • Relax iris sphincter muscle and ciliary muscle
48
Q

What is
Denervation hypersensitivity

A
  • Death of nerve causing a change in the receptors and resulting in increased responsiveness
  • Tissue may become over - responsive to drugs that act directly on receptors e.g. over – reaction

Ocular Pharmacology (5 decks)

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