Vasoactive drugs

1. VASOACTIVE DRUGS PRESENTED BY MWADZIWANA LOUIS LAW

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 β 2 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 V 1a 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 DA 2 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

10. Nitroglycerin Dilate the venous system, reducing pressure needed to circulate the blood around.

11. Dobutamine Increase contractility and heart rate via β 1 receptors Increase vasodilation resulting in decrease afterload/SVR Increase in blood pressure

12. Norepinephrine Vasoconstrictor via α adrenergic receptors Severe hypertension Increase in blood pressure

13. Phenylephrine Powerful vasoconstrictor Increase in blood pressure

14. Epinephrine Vasoconstrictor via α adrenergic receptors Increased heart rate and contractility via β 1 receptors Increased vasodilation via β 2 receptors