Sympatholytics.pptx

Sympatholytic drugs (Adrenergic blockers) bind to the adrenergic receptors and prevent the action of adrenergic drugs.
These are drugs which block the actions of sympathetic division or catecholamines (adrenaline and noradrenaline).
They are competitive antagonists at both α and β adrenergic receptors.

1. Pharmacological actions of adrenaline and alpha Sympatholytics Receptor Location Pharmacological actions of Adrenaline Pharmacological actions of α- Sympatholytics α1 Veins , arterioles, arteries, capillaries Urinary sphincter Eye Radial muscles Vasoconstriction and rise in blood pressure Contraction Mydriasis   Vasodilation and fall in blood pressure Relaxation Miosis α2 Presynaptic membrane Blood vessels Control release of NA in nerve endings Vasoconstriction and rise in blood pressure   Increase release of NA Vasodilation and fall in blood pressure

2. Raynauds disease

3. Frostbite

4. Benign prostatic hypertrophy

5. We should also keep in mind that- At higher concentration, adrenaline acts on all receptors (α1, α2, β1,β2, β3 ). But at lower concentration, adrenaline acts selectively on β2 – receptors (because β2 are more sensitive) Receptors Location Pharmacological action of Adrenaline α1 Blood vessels (Veins, Arteries, Arterioles, Capillaries) Vasoconstrictions (increases blood pressure) β2 Blood vessels (Arteries) Vasodilatation (fall in blood pressure)

6. Pharmacological actions of adrenaline and Beta blockers Receptor Location Pharmacological actions of adrenaline Pharmacological actions of β blockers β1 Heart   INCREASED Heart rate (+ ve Chronotropic effect) Contractility(+ ve ionotropic effect) Conduction velocity Excitability DECREASED Heart rate (-ve Chronotropic effect) Contractility (-ve ionotropic effect) Conduction velocity Excitability β2   Blood vessels (arteries) Kidney     VASODILATION Increased Renin secretion and rise in blood pressure     Decreased Renin secretion and fall in blood pressure

7. β blockers competitively block the actions of adrenaline on beta receptors innervated organs especialy heart . β1 Blocking action reduces heart rate (- ve chronotropic effect ), myocardial contractility (- ve ionotropic effect), conduction velocity and excitability of the heart. Beta blockers decrease myocardial oxygen consumption by decreasing heart rate, blood pressure and contractility.

8. β blockers also inhibit the Renin secretion from the kidney nephrons. Thereby they produce vasodilation and fall in blood pressure. β blockers decrease outflow of the sympathetic impulses from sympathetic nerves. β blockers produce resetting of baroreceptors on the aortic body on the aorta. Therefore β blockers shows antihypertensive activity.

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