18. Sympathomimetics and sympatholytics

Question 1

What is the sympathetic nervous system?

Answer 1

The sympathetic nervous system responds to dangerous or stressful situations. In these situations, your sympathetic nervous system activates to speed up your heart rate, deliver more blood to areas of your body that need more oxygen or make other responses to help the animal get out of danger.

It is often called the “fight-or-flight” response, as it reacts to emergency situations and short-term stress

Question 2

Signs of activation of the sympathetic nervous system:

Answer 2

• Dilated pupils (mydriasis)
• Increased salivation
• Increased heartbeat
• Relaxed airways
• Relaxed bladder
• Promote ejaculation and vaginal contraction
• Stimulate the release of glucose

Question 3

Mechanism of action of the sympathetic nervous system

Answer 3

1. Alpha-1 receptor
Found in the smooth muscle, causing vasoconstriction and mydriasis (dilation of pupils)

2. Alpha-2 receptors
Inhibits the norepinephrine release, which leads to GI relaxation and inhibition of insulin release, resulting in less insulin release from the pancreas.

3. Beta-1 receptors
Found in the heart mainly, and causes cardiac effects, like positive inotropic effect (increasing the heart strength) and positive chronotropic effect (increasing the heart rate)

4. Beta-2 receptors
Found in the lungs, blood vessels and uterus.
We see vasodilation, bronchodilation and uterine relaxation.

5. Beta-3 receptors
They are found in fat tissue and stimulate lipolysis, which is the breakdown of fat for energy.

These receptors are involved in the synthesis of catecholamines, and they use noradrenaline as a neurotransmitter.

Question 4

Sympathomimetics, active substances

Answer 4

Non-selective sympathomimetics
- Epinephrine
- Dopamine
- Norepinephrine

Selective sympathomimetics
Beta-2 agonists:
- Clenbuterol
- Salbutamol
- Terbutalin
- Salmeterol

Question 5

Sympathomimetic, pharmacological effect

Answer 5

1. Cardiovascular effect
- Vasoconstriction
- Vasodilation
- Positive chronotropic
- Positive inotropic

2. Gastrointestinal system
Smooth muscle releaxation

3. Respiratory system
Bronchidilation, decreased bronchial secretion

4. Urinary bladder
Increased spincther-constriction

5. Eye
Mydriasis, increased aqueous humor production

Question 6

Sympatholytics, Active substances

Answer 6

Non-selective
Beta-receptors antagonists
- Propanolol
- Timolol
Alpha-2 receptor antagonist
- Atipamezole

Selective receptors
Beta-1 receptors antagonists
- Metorpolol

Question 7

Sympatholytics, Pharmacokinetics

Answer 7

Lipophilicity
- Metabolism: Liver and kidney