This document summarizes the effects of sympathomimetic drugs on the cardiovascular system. It describes the effects of activating different types of adrenergic receptors, including α1, α2, β1, β2, and dopamine receptors. The key effects discussed are: - α1 receptor activation causes vasoconstriction of both arteries and veins, increasing blood pressure. - α2 receptor activation decreases sympathetic tone centrally and lowers blood pressure via peripheral vasoconstriction. - β receptor activation in the heart increases contractility and heart rate, while β2 receptor activation causes vasodilation in some blood vessels. - Dopamine activation of D1 receptors causes vasodilation of

1. Effects of
sympathomimetic
drugs on the
cardiovascular
system
Domina Petric, MD

2. 2
Type of
adrenergic
receptor
Tissue Effects on the tissue
α1 Smooth musculature of
innervated blood vessels
Contraction
Dilator pupillae muscle Contraction
(mydriasis)
Smooth musculature of hair
pilomotors
Contraction
Heart Increased strength of
contraction
α2 Postsynaptic in the brain Multiple effects
Thrombocytes Agregation
Adrenergic and cholinergic
presynaptic endings
Inhibition of
neurotransmitters
release
Fat cells Lipolysis inhibition

3. 3
Type of
adrenergic
receptor
Tissue Effects on the tissue
β1 Heart, juxtaglomerular cells Increased strength
and speed of
contraction,
increased renin
release
β2 Smooth musculature of bronchi,
uterus and blood vessels
Relaxation
Sceletal muscles Increased potassium
uptake
Liver Activation of
glycogenolysis
β3 Fat cells Activation of lipolysis

4. “
4
Type of
adrenergic
receptor
Tissue Effects on the tissue
D1 Smooth muscles Dilatation of blood
vessels
D2 Nerve endings Modulation of
transmitters release

5. Effects of α1 receptors activation
➝ These receptors are widely distributed in the
vasculature.
➝ Their activation causes arterial and venous
contraction.
➝ Clean α1-receptor agonists increase peripheral
arterial resistance and decrease capacity of veins.
➝ Increase of blood pressure causes reflex
bradicardia.
➝ Reflex bradicardia is due to activation of
baroreceptors.
➝ Venous inflow is increased.
5

6. 6
Alfa-receptor agonist MIDODRINE can be used to treat orthostatic hypotension.
In the blood vessels of skin and abdominal organs there are mostly alfa-receptors
so constriction is a consequence of adrenaline and noradrenaline release.
Blood vessels in sceletal muscles have both alfa and beta adrenergic receptors so
release of adrenaline and noradrenaline can cause both contriction and vasodilatation.
Blood vessels in the nasal mucosa have alfa-receptors. That is why sympathomimetics
are used as nasal decongestans (local vasoconstriction).

7. These receptors are
present in all blood
vessels.
Their activation causes
vasoconstriction when
used locally (very fast
intravenous infusion or
high oral dose).
Systemic use of α2-
receptors agonists causes
both central α2-receptors
activation and peripheral
α2-receptors activation.
Effects of α2-receptors activation
Activation of central
α2-receptors causes
decrease of
sympathetic tonus
and lowers blood
pressure.
α2-agonists are
therefore used as
sympatholytics in
treatment of
hypertension.
7

8. Effects of β-receptors activation
Activation of
β-receptors
in the heart
increases
heart
contractility
and heart
frequency.
Activation of
β2-receptors
on the
periphery
causes
vasodilatation
in some blood
vessels.
Sympathomimetics effects in the heart
1) Positive inotropic effect:
increase of intrinsic heart
activity. Contraction is
stronger, relaxation is faster.
2) Positive chronotropic effect:
increase of heart frequency.
3) Positive dromotropic effect:
increase of conduction speed
in the atrioventricular node.
4) Positive bathmotropic effect:
increased excitability of the
heart.
8

9. Effect of dopamine receptors activation
Intravenous aplication of dopamine
causes vasodilatation of renal, visceral,
coronary and cerebral arterioles via
activation of D1-receptors.
Activation of D1-receptors in renal blood
vessels can increase natriuresis.
Activation of presynaptic D2-receptors
inhibits noradrenalin release.
Dopamine activates β1-receptors in the
heart.
9

10. Effect of dopamine receptors activation
10
Low dose of
dopamine
decreases
peripheral
resistance.
When given
in high
speed
infusion
activates α-
receptors.
High speed
infusion of
dopamine
mimics
affects of
noradrenaline.
Activation of α-
receptors causes
vasoconstriction,
including renal
vasoconstriction.
DOPAMINE