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Vasoactive drugs
This document discusses vasoactive drugs, which affect vasomotor tone by causing vasoconstriction or vasodilation. It describes several classes of vasoactive drugs including vasodilators like hydralazine and nitroglycerin that work by different mechanisms in the arteries and veins. Vasoconstrictors like phenylephrine and vasopressin are also discussed. Many vasoactive drugs have direct effects on the heart by acting on receptors in the cardiovascular system. Inodilators like milrinone cause both vasodilation and increased cardiac contractility. Specific drugs such as dopamine, norepinephrine, and epinephrine are explained in terms of their vascular and cardiac effects.
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Vasoactive drugs
- 1. VASOACTIVE DRUGS PRESENTED BY MWADZIWANA LOUIS LAW
- 2. DEFINATIONS • These aredrugs that affect the vasomotor tone. • They are subdivided into two vasoconstrictors and vasodilators
- 3. Vasodilators • They aresubdivided into arterial (eg hydralazine, nicardipine) or venous (eg nitroglycerine) • Many of them are mixed arteriovenous vasodilators (eg nitropruside, α-adrenoceptor antagonists)
- 4. Mechanism of actionof 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 ActionOf 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 ofnorepinephrine • 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 vasodilatorDrugs (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 thevenous system, reducing pressure needed to circulate the blood around.
- 11. Dobutamine • Increase contractilityand heart rate via β1 receptors • Increase vasodilation resulting in decrease afterload/SVR • Increase in blood pressure
- 12. Norepinephrine • Vasoconstrictor viaα adrenergic receptors • Severe hypertension • Increase in blood pressure
- 13. Phenylephrine • Powerful vasoconstrictor •Increase in blood pressure
- 14. Epinephrine • Vasoconstrictor viaα adrenergic receptors • Increased heart rate and contractility via β1 receptors • Increased vasodilation via β2 receptors