2. DEFINATIONS
• These are drugs that affect the vasomotor
tone.
• They are subdivided into two vasoconstrictors
and vasodilators
3. Vasodilators
• They are subdivided into arterial (eg
hydralazine, nicardipine) or venous (eg
nitroglycerine)
• Many of them are mixed arteriovenous
vasodilators (eg nitropruside, α-adrenoceptor
antagonists)
4. Mechanism of action of
VASODILATORS
• Stimulation of peripheral β2 adrenoceptor (eg
isoproterenol)
• Antagonism of α adrenoceptor (phentolamine)
• Inhibition of inward flow of calcium ions through calcium
channels(nicardipine)
• Stimulation of dopaminergic receptors (fenoldopam)
• Nitric oxide induced formation of cyclic guanosine
monophosphate inhibition of breakdown of cyclic AMP (
milrinone)
• Angiotensin converting enzyme inhibition ( enalapril)
5. Mechanism of Action Of
Vasoconstrictors
• Stimulation of peripheral α adrenoceptors (
phenylephrine)
• Arginine vasopresin V1a receptors (
vasopressin)
• Released when there is low blood volume
6. Direct Cardiac Effects
• Many vasoactive drugs directly affect cardiac
performance because they act on receptors, ion
channels, or enzymes that are located in the
vascular system and the heart.
• Vasoactive drugs can be a pure vasoconstrictor
(phenylephrine),
• a combined vasoconstrictor and positive inotrope
(norepinephrine),
• A pure vasodilator ( isoproterenol)
• A combined vasodilator and negative inotrope
7. Dopamine
• Precursor of norepinephrine
• In high dosage
• In the periphery, dopamine stimulates prejunctional
dopaminergic DA2 receptors, which results in the
inhibition of norepinephrine release, facilitating
vasodilation
• At low doses, dopamine stimulates the dopaminergic
receptors in the arteries located in the kidneys,
abdomen, heart, and brain.
• The vasodilation of renal and mesenteric arteries
causes an increase in urine output and a decreased
preload.
8. Mixed inotropic vasodilator Drugs
(Inodilators)
• Milrinone and enoximone are
phosphodiesterase inhibitors
• They inhibit the breakdown of cAMP in cardiac
and peripheral vascular smooth muscle
resulting in increased cardiac contractility and
arterial and venous vasodilation.
9. Milrinone
• PDE inhibitor
• Positive inotropic effect
• No effects on the heart rate
• Systemic vascular resistance decrease
