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Adrenergic Receptor Antagonists

59-291, Section 2, Lecture 5. Adrenergic Receptor Antagonists. Excessive sympathetic activity is characteristic of a number of pathological states including: Hypertension Angina pectoris Cardiac arrhythmias Sympatholytics – adrenergic receptor antagonists Block ,  or both

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Adrenergic Receptor Antagonists

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  1. 59-291, Section 2, Lecture 5 Adrenergic Receptor Antagonists • Excessive sympathetic activity is characteristic of a number of pathological states including: • Hypertension • Angina pectoris • Cardiac arrhythmias • Sympatholytics – adrenergic receptor antagonists • Block ,  or both • Therapeutic effects due to 1 and 1 blockade • Adverse effects due to 2 and 2 blockade • Therefore 1 and 1 selective antagonists

  2. Competitive inhibitor Non-competitive inhibitor Non-selective -blockers • Block both 1 and 2 receptors • Ie. phentolamine and phenoxybenzamine Chemical sympathectomy Hypertensive Episodes - decreases vascular resistance - lowers BP - smooth muscle relaxation in the bladder Used to treat hypertensive episodes of Pheochromocytoma

  3. Selective 1-blockers • Selectively block 1 receptors • Ie. Alfuzosin, doxazosin, prazosin, terazosin • Used in the treatment of chronic hypertension • Also used to treat urinary retention in men with benign prostatic hyperplasia

  4. Selective a1 blockers cause less reflex tachycardia than phenoxybenzamine and phentolamine

  5. Adverse effect of a1 blockers • Mostly caused by excessive vasodilation • Hypotension, dizziness, fainting, reflex tachycardia, palpitation • First-dose syncope: effect on BP when they are initially administered

  6. -adrenergic receptor antagonists • Both non-selective and selective -blockers • Non-selective • ie nadolol, pindolol, propranolol, tomilol • Block both 1 receptors in cardiac tissue and 2 in smooth muscle, liver and other tissues • Blockade of 1 reduces sympathetic stimulation of heart… Therefore, negative • Blockade of 2 may cause broncoconstriction and limit glycogenolysis  Adverse effects!! chronotrope inotrope dromotrope

  7. 1-antagonist _____ 1-antagonists --------

  8. Selective 1-blockers • Have greater affinity for 1 than for 2 receptors • Ie Acebutolol, atenolol, esmolol, metoprolol CARDIOSELECTIVE b BLOCKERS • Produce fewer adverse effects than non-selective, but their selectivity is not absolute • In summary, • -blockers have a number of clinical applications including treatment of: • migraines • Hypertension • angina pectoris • cardiac arrhythmia • glaucoma

  9. 1- Contract vascular smooth muscle, iris, bladder sphincter muscle 2- Relaxes bronchial, uterine, and vascular smooth muscle 2-Inhibits NE release 2-mediates platelet aggregation;decrease insulin secretion; decreases secretion of aqueous humor 2-inhibits platelet aggregation; promotes glycogenolysis

  10. Practice Questions • Blockade of which receptors is responsible for the therapeutic and adverse effects of adrenergic receptor agonists? • Therapeutic: a1, b1 • Adverse: a2, b2

  11. Which type of drugs causes chemical sympathectomy? Give an example? • Non-Competitive a blocker • phenoxybenzamine

  12. What type of adrenergic receptor antagonists can be used in treatment of nocturia in benign prostate hyperplasia? Give an example. • a1 blockers • Alfuzosin, doxazosin, prazosin, terazosin

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