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M2 Pharmocology > 4.4 SNS Antagonists & False transmitters > Flashcards

4.4 SNS Antagonists & False transmitters Flashcards

1
Q

a1 receptors

  • tissues
  • functions
A
  • Various (vascular, GI tract etc.)

- Vasoconstriction, relaxation of GI tract

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2
Q

α2 receptors

  • tissues
  • functions
A
  • Presynaptic terminals, vascular smooth muscle, CNS

- Inhibition of transmitter release, vasoconstriction, CNS actions

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3
Q

β1 receptors

  • tissues
  • functions
A
  • Heart, GI tract, kidneys

- Increased cardiac rate and force, relaxation of GI tract, renin release from kidneys

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4
Q

β2 receptors

  • tissues
  • functions
A
  • Bronchi, smooth muscles, liver

- Bronchodilation, vasodilation, relaxation of visceral smooth muscle, hepatic glycogenolysis

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5
Q

β3 receptors

  • tissues
  • functions
A
  • Adipose tissue

- Lipolysis

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6
Q

what is the selectivity for labetalol?

A

α1 + β1

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7
Q

what is the selectivity for phenotolamine?

A

α1 + α2

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8
Q

what is the selectivity for prazosin?

A

α1

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9
Q

what is the selectivity for propranolol?

A

β1 + β2

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10
Q

what is the selectivity for atenolol?

A

β1

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11
Q

Hypertension refers to an increase in blood pressure associated with increased risk of other diseases (sign rather than a disease itself):
• Underlying cause is rarely diagnosed (often primary hypertension)
• Defined by NICE guidelines as a blood pressure of__________________, or diagnosed with an ambulatory blood pressure monitoring (ABPM) daytime average or home blood pressure monitoring (HBPM) average of __________________
• Main contributing elements: blood volume, cardiac output, peripheral vascular tone

A

140/90 mmHg or higher;

135/85 mmHg or higher

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12
Q

The different β blockers (-olols) may be cardioselective (β1) or non-selective:

Competitive antagonism of the β1 adrenoceptors is responsible for most of the antihypertensive actions (unclear how effective β2 antagonism is):
• CNS effects: reduces sympathetic tone to various tissue targets
• Cardiac effects: reduces ____________ → not in chronic treatment
• Renal effects: reduces _____________ → chronic long-term benefit (due to blocking of the vasoconstrictor effects of angiotensin II)

The common long-term feature in the antihypertensive actions of these β adrenoceptor antagonists is the ____________________:
• Blockade of facilitatory effects of presynaptic β adrenoceptors on NA release may also contribute to the antihypertensive effect

A

heart rate and cardiac output;

renin production;

reduction in peripheral resistance (due to kidneys and angiotensin)

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13
Q

Why is β blockers dangerous in diabetics?

A

Use of β blockers masks the symptoms of hypoglycaemia (palpitations and tremors): • Non-selective antagonists are more dangerous in diabetics as they block β2-driven glycogenolysis
• β1-selective agents are advantageous as hepatic glucose release is controlled by β2 receptors

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14
Q

Why can’t β blockers be used in patients with acute/ unstable heart failure?

A

obstructive lung diseases (e.g. bronchitis) Cardiac failure
Treatment in chronic heart failure leads to reduced mortality:
• Cannot be used in acute/unstable heart failure due to acute negative inotropic effects

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15
Q

why is there bronchoconstriction due to β blockers?

A

Little importance in the absence of airway disease, but can be dramatic and life-threatening in asthmatic patients/other obstructive lung diseases (e.g. bronchitis)

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16
Q

why is there cold extremities due to β

blockers?

A

Loss of β-mediated vasodilation in cutaneous vessels

17
Q

why is there bad dreams due to β blockers?

A

CNS effects

18
Q

why is there fatigue due to β blockers?

A

Reduced cardiac output and muscle perfusion

19
Q

What are the effects of propranolol?

A
  • Non-selective (β1 + β2)
  • At rest: little change in HR, CO, BP *Reduces the effects of exercise/stress on these variables (at rest parasympathetic dominates)
20
Q

What are the effects of atenolol?

A
  • Cardioselective (β1)

- Mainly antagonises NA effects on the heart (also affects any tissues with β1 receptors)

21
Q

What are the effects of labetalol?

A
  • Dual-acting (β1 + α1)
  • 4:1 selectivity for β1
  • Lowers BP via reduced TPR (kidneys – reduced angiotensin; vascular SM – constriction)
  • No long-term change in HR/CO → long-term benefit by changing TPR
22
Q

α blockers can be non-selective (blocks both α1 and α2 receptors), leading to _______________ (α receptors are the main mediators of peripheral resistance):
• Leads to __________________ (reflex response to fall in BP)
• Blood flow through _____________ is increased (dilation in peripheral resistance vessels), but direct effects on vascular smooth muscles of such vascular beds are slight (mainly mediated by β1)
• Side effect: _____________(sympathetic input usually prevents pooling of blood in the legs)

A

reduced arterial pressure;

increased heart rate and cardiac output;

cutaneous and splanchnic vascular beds;

postural hypotension

23
Q

What are the effects for Phentolamine?

A
  • Non-selective (α1 + α2)
  • Vasodilation in peripheral resistance vessels → fall in BP (α1)
  • Concomitant α2 blockade increases NA release → enhances reflex tachycardia
  • No longer clinically used (for acute treatment of hypertension in surgery)
  • Side effect: Increased GI motility → diarrhoea
24
Q

What is prazosin used for?

A
  • Highly selective (α1)
  • Vasodilation → fall in BP
  • Less tachycardia than non-selective antagonists as drugs do not increase NA release (no α2)
  • CO decreases → fall in venous pressure (dilation of capacitance vessels) → does not affect cardiac function appreciably
  • Modestly decreased LDL, increased HDL
  • Not the drug of choice (only in extreme cases → hypertension in ICU)
  • Side effect: Postural hypotension (drastic hypotensive effect not well tolerated)
25
Q

Methyldopa is a false transmitter used as an antihypertensive agent → taken up by noradrenergic neurones, decarboxylated and hydroxylated to form the false transmitter α-methyl-noradrenaline:
• α-methyl-noradrenaline is not deaminated by _________ → tends to accumulate in larger quantities than NA → displaces NA from synaptic vesicles

• Released in the same way as NA but:
o Less active than NA on α1 adrenoceptors → _____________
o More active on presynaptic α2 adrenoceptors → _______________ (reduces transmitter release below normal levels)
• CNS effects: _____________

Uses

  • Maintenance of renal and CNS blood flow: widely used in hypertensive patients with renal insufficiency or cerebrovascular disease
  • Foetal effects: _________________ → used in hypertensive pregnant women

Side effects
- Dry mouth, sedation, orthostatic hypotension, male sexual dysfunction

A

MAO;

less effective at causing vasoconstriction;

autoinhibitory feedback mechanism operates more strongly;

stimulates brainstem vasopressor centre to inhibit sympathetic outflow;

no adverse effects on foetus despite crossing blood-brain barrier

26
Q

Cardiac arrhythmias are abnormal/irregular heartbeats, which account for 350000 deaths in the USA alone, commonly caused by __________________
• Electrical conductance is much slower through the damaged tissue due to abnormal electrical circuits (causes arrhythmias)
• Can be treated using _______________

A

myocardial ischaemia;

class II anti-arrhythmics (β antagonists)

27
Q

How does class II anti-arrhythmics (β antagonists) affects the SA node?

A

Affect the pacemaker current which regulates heartbeat activity:
• Increased sympathetic drive to the heart via β1 receptors can precipitate or aggravate arrhythmias (especially after MI due to increased sympathetic tone)

28
Q

How does class II anti-arrhythmics (β antagonists) affect the SA node

A

AV conductance depends critically on sympathetic activity: • AV nodal refractory period increased (-ve dromotropy) by β adrenoceptor antagonists → slows the ventricular rate

29
Q

Propranolol is a non-selective β antagonist Class II drug with its effects mainly attributed to _______________
• Helps to reduce mortality of patients with myocardial infarction
• Particularly successful in treating arrhythmias during ________________

A

β1 antagonism:

exercise or mental stress

30
Q

Angina is pain that occurs when the ______________________, often localised at the chest, arm, and neck (starting at the chest and radiating distally):
• Often brought on or exacerbated by exertion or excitement
• Mainly caused by ____________ (laying down of fatty deposits in coronary vessels) → narrows the blood vessels (especially in the junctions) → reduced O2 delivery

A

oxygen supply to the myocardium is insufficient for its needs;

atherosclerosis

31
Q

What is the characteristic of stable angina?

A

Pain on exertion → increased demand on heart due to fixed narrowing of the coronary vessels (e.g. atheromas)

32
Q

What is the characteristic of unstable angina?

A

Pain with less and less exertion (culminates with pain at rest):
• Platelet-fibrin thrombus associated with ruptured atheromatous plaque (without complete vascular occlusion) → risk of infarction

33
Q

What is the characteristic of variant (Prinzmetal) aginaa

A

Occurs at rest due to coronary artery vasospasm associated with atheromatous disease:
• Presents with ECG changes (e.g. ST elevation) but no clinical sign of myocardial infarction (e.g. cTn elevation)

34
Q

Why β blockers are used to treat angina

A

reducing myocardial oxygen demand via decreasing HR, SBP, and cardiac contractile activity:

35
Q

What are the side effects of β blockers

A
  • Fatigue, insomnia, dizziness
  • Sexual dysfunction
  • Bronchospasm, bradycardia, heart block, hypotension, decreased myocardial contractility
36
Q

What are the contraindications of beta blockers?

A
  • Bradycardia (HR < 55 beats/min)
  • Bronchospasm
  • Hypotension (SBP < 90 mmHg)
  • AV block or severe congestive
37
Q

Glaucoma occurs due to an increased intraocular pressure due to the poor drainage of aqueous humour (between cornea and lens):
• Aqueous humour is formed by the ________________ → if drainage channels become blocked, build-up of aqueous humour occurs → increased IOP
• If left untreated, this permanently _________________

AQUEOUS HUMOUR
The aqueous humour is produced by blood vessels in the ciliary body via ________________ (activity controlled by adrenoceptors on ciliary body surface):
• Flows into the posterior chamber → through the pupil → anterior chamber
• Drain into the trabecular network → __________________
• Production of aqueous humour is indirectly related to blood pressure and blood flow in the ciliary body

TREATMENT
• β antagonists can be used to treat glaucoma, either using non-selective (e.g. carteolol hydrochloride, levobunolol hydrochloride, timolol maleate) or β1-selective (e.g. betaxolol hydrochloride) agents:
• Reduce the___________________ by blocking the receptors on the ciliary body → blocks the effects of circulating adrenaline

A

ciliary body;

damages the optic nerve and causes blindness;

carbonic anhydrase;

veins and canal of Schlemm;

rate of aqueous humour formation

38
Q

What are other uses of β antagonists

A
  • anxiety states: Controlling somatic symptoms associated with sympathetic over-reactivity (e.g. palpitations, tremors)
  • migraine prophylaxis: Maintaining blood flow in the brain
  • benign essential tremor: Reduces sympathetic effects on muscle spindles

M2 Pharmocology (20 decks)

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