Patient: Beta Adrenoceptors

Question 1

Describe the binding when beta1 and beta2 adrenoceptors are activated

Answer 1

GPCR
Galphas activates adenylyl cyclase
Increase in cAMP
increase in PKA (protein kinase A)

Question 2

Describe the functional response when a beta1 adrenoceptor is activated

Answer 2

1) Heart: SA node, AV node, Myocardium
Increase HR
Decrease refractory period
Increase force of contraction

2) Juxtaglomerula cells - release of renin
3) GI smooth muscle relaxtion

Question 3

Describe the functional response when a beta2 adrenoceptor is activated

Answer 3

1) Bronchodilation
2) Vasodilation
3) GI smooth muscle relaxation
4) Relaxation of visceral smooth muscle
5) Decrease in histamine release
6) Muscle Tremor
7) Glycogenolysis

Question 4

Beta2 adrenoceptor activation: vasodilations effects?

Answer 4

• skeletal muscle vasculature
• endothelium-dependent
• release of Nitric Oxide (NO)

Question 5

beta2 adrenoceptor activation: Relaxation of visceral smooth muscle effects?

Answer 5

• Bladder detrusor
• ciliary muscle
• seminal tract
• uterus (premature labour)

Question 6

beta2 adrenoceptor activation: Glycogenolysis occurs where?

Answer 6

Hepatocytes and skeletal muscle

Question 7

Functional response of beta3 adrenoceptors

Answer 7

Lipolysis (breakdown of fat) on adipocytes

Question 8

Name beta2-selective agonists used as bronchodilator agents

Answer 8

Short acting (2-4 hours) 
Salbutamol and terbutaline 

Long acting (up to 12 hours)
Salmeterol and efortmoterol

Question 9

Unwanted effects of beta-agonist bronchodilators

Answer 9

1) Tremor - peripheral effect involving interference with muscle spindle function
2) Tachycardia - activation of cardiac beta-AR
3) Nervous tension - effect on CNS
4) Hypokalaemia - stimulation of Na+/K+ ATPase in skeletal muscle

Question 10

How are unwanted effects of beta-agonist bronchodilators reduced?

Answer 10

inhalational rather than oral administration

Question 11

Name another use of a b-adrenoceptor agonist apart from bronchodilators

Answer 11

Supression of premature labour (tocolysis)
e.g. salbutamol or ritodrine
which are both beta2-selective agonists

Question 12

Give 3 properties of Propranolol

Answer 12

• competitive agonist
• Non-selective Beta-adrenoceptor antagonist
• Relatively lipid soluble (good penetration of CNS)

Question 13

Give 3 properties of Atenolol

Answer 13

• Competitive antagonist
• relatively selective beta1-adrenoceptor anatagonist
• relatively water soluble (poor penetration of CNS)

Question 14

Give a use of beta-adrenoceptor antagonist

How does it work?

Answer 14

Anti-hypertensive drugs

Decrease in: cardiac output, renin release and sympathetic tone (vasomotor centre in medulla oblongata)

Question 15

What is angina pectoris and how are beta-adrenoceptors used in its prophylaxis?

Answer 15

Angina of effort: crushing pain in chest that may radiate to arm, neck or jaw.
The pain results from cardiac ishaemia
Cardiac Beta1-AR blockade (propranolol)
-decreases cardiac rate, force and work
-prolongs diastole (bradycardia)
-increases coronary blood flow
-increases 02 delivery

Question 16

How are B-AR antagonists used to control symptoms of thryotoxicosis

Answer 16

Thyroid hormone sensitises tissues to catecholamines (hence eyelid contraction occurs)
Symptoms that can be controlled by beta-blocker e.g. propanolol:
-Anxiety, tachycardia, Palpitations, tremor

Question 17

Propanolol (beta-AR anatagonist) can be used for the prophylaxis of what other thing? (not cardiac)

Answer 17

Prophylaxis of migraine

Mechanism unclear but may involve anxiolysis (inhibits anxiety)

Question 18

Unwanted effects of Beta-AR antagonists

Answer 18

1) Bronchoconstriction
- bronchial ashtma
- bronchitis
- emphysema
2) Precipitation of cardiac failure/heart block
- patients with heart disease
- oxprenolol (partial agonist)
3) Hypoglycaemia
- patients with diabetes
- mask of sympathetic sweating, tachycardia and tremor
4) Cold extremities
- Raynaud’s disease and claudication
5) vivid dreams
- propanolol (practolol)
- not a problem with atenolol