The sympathetic nervous system

α-receptors

α1-receptor smooth muscle contraction

vasoconstriction

mydriasis

α-receptors

α2-receptor

inhibition of neurotransmitter release (NA!)

Neurotransmission

NA

NA

NAα2

α2-agonists

NA

NA

NA

α2

XYLAZINE

α-receptors

α2-receptor

GI-relaxation

inhibition of insulin release

β-receptors

β1-receptor

cardiac effects (positive inotropic, chronotropic)

β2-receptor

vasodilatation

bronchodilatation

uterus relaxation

(β3-receptor

lipolysis in fat tissue)

Synthesis of catecholamines

Drugs acting on the

sympathetic nervous system

1. Sympathomimetics

2. Sympatholytics

Sympathomimetics

o Cardiovascular system o positive chronotropico positive inotropic o vasoconstriction (α1-agonists)o vasodilatation (β2-agonists)

Pharmacological effects

β1-agonisták

o Gastrointestinal systemo smooth muscle relaxationo GI atony

o Respiratory systemo bronchodilatation, decreased bronchial secretion

o Urinary bladdero increased sphincter-constriction (α1-receptor)

o Eyeo mydriasis (iris radial muscles) o increase in aqueous humor production

Pharmacological effects

Nonspecific sympathomimetics

Active substances

Adrenaline (epinephrine)

noncspecific (mainly β1 and β2 receptors)

α-receptors in higher dosage

cardiac effect

arrhytmogenic!

blood pressure?

indications:

- cardiac stop

- severe bronchoconstriction

- anaphylaxia

- local vasoconstriction (haemorrhages)

- increase in duration of local anaesthetics

Ca, Fe: 0.02 mg/kg intratracheal, IV.

Active substances

Noradrenaline (norepinephrine)

nonspecific (mainly β1 and α1 receptors)

cardiac effect

blood pressure is significantly increased!

indications (rare):

- hypotension

Active substances

Dopamine

low dose D1-receptors (kidney!) 2-5 µg/kg

medium dose β1-receptors (heart!) 5-10 µg/kg

high dose α1-receptors (pressor) 10-20 µg/kg

indications

Specific sympathomimetics

β-adrenoceptor agonists

Dobutamine

mainly β1 receptors

cardiac effect

indications:

- cardiogenic shock (IV. infusion)

Isoproterenol

only β receptors (β1 and β2 )

heart+bronchi+muscle vessels

indications?

β2 agonists (clenbuterole, salbutamole, terbutaline, salmeterole, isoxsuprine etc.)

mainly β2 receptors

bronchodilatation

uterus relaxation

higher dosage β1 receptorscardiac effect

clenbuterole 4:1

salbutamole 650:1

salmeterole 50000:1

side effects!

β-adrenoceptor agonists

β2 agonists

indications: horse RAO

feline asthma

bronchitis, bronchopneumonia

tracheal hypoplasia

tracheal collapse

earlier…

dosage: clenbuterole horse 1-3 µg/kg PO.

salbutamole 100-200 µ/cat

360-720 µg/horse

β-adrenoceptor agonists

Phenylephrine

mainly α1-receptors vasoconstriction

used rarely

local and systemic usage

α-adrenoceptor agonists

Allergy, cold

Hypotension, shock (?)?)

Xylometazoline, oxymetazoline, naphazoline, tetryzoline

mainly α1-receptors vasoconstriction

local usage

α-adrenoceptor agonists

Phenylpropanolamine

mainly α1-receptors urinary bladder sphincter constriction!

per os usage (empty stomach)

side effects

Ephedrine

nonspecific, direct and indirect effects

tachyphylaxis

CNS

allergy, incontinence (p.o.)

Amphetamine

α-adrenoceptor agonists

α2-agonists

SEDATO-HYPNOTICS (see later)

xylazine, detomidine, medetomidine, romifidine

α-adrenoceptor agonists

Sympatholytics

Nonspecific α-antagonists

Phenoxybenzamine (urethra sphincter relaxation)

long duration of action

Phentolamine

Tolazoline

α1-antagonists

prazosine, doxasozine (urethra sphincter relaxation)

α2-antagonists

atipamezole, yohimbine

α-adrenoceptor antagonists

Nonspecific β-antagonistsPropranololeTimolole

SIDE EFFECTS

Specific β1-antagonistsMetoprololeAtenolole

β-adrenoceptor antagonists