ISOPROTERENOL

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Isoproterenol is a synthetic catecholamine and non-selective beta-adrenergic agonist with potent inotropic and chronotropic effects on the heart. While not routinely used in anesthesia, it can be an important agent in specific situations where its unique properties are beneficial. Here are some of the reasons for its importance in anesthesia:

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1. Treatment of bradycardia: Isoproterenol can be used to treat severe bradycardia or heart block in the perioperative period when other treatments, such as atropine or pacing, are ineffective or contraindicated. By stimulating beta-1 receptors in the heart, isoproterenol increases the heart rate and improves cardiac conduction.

2. Management of bronchospasm: Isoproterenol's action on beta-2 adrenergic receptors in the bronchial smooth muscle can cause bronchodilation. Although not a first-line treatment, it may be considered in severe cases of bronchospasm that do not respond to conventional bronchodilators like albuterol.

3. Cardiac stress testing:  Isoproterenol may be used in cardiac stress testing to pharmacologically induce stress on the heart when exercise stress testing is not feasible.

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Here are the main steps in isoproterenol's mechanism of action:

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1. Activation of beta-adrenergic receptors: Isoproterenol binds to and activates both beta-1 and beta-2 adrenergic receptors. Beta-1 receptors are predominantly found in the heart, whereas beta-2 receptors are primarily located in the bronchial smooth muscle and vascular smooth muscle.

2. Stimulation of adenylate cyclase: Upon activation of the beta-adrenergic receptors, isoproterenol triggers a signaling cascade involving the activation of adenylate cyclase, an enzyme that converts adenosine triphosphate (ATP) into cyclic adenosine monophosphate (cAMP).

3. Increase in intracellular cAMP levels: The increase in cAMP levels within the target cells leads to the activation of protein kinase A (PKA), which in turn phosphorylates various proteins, ultimately affecting cellular function.

4. Effects on the heart (beta-1 stimulation): Isoproterenol's action on beta-1 receptors in the heart results in positive inotropic and chronotropic effects. This means that it increases the force of cardiac contractions (inotropy) and accelerates the heart rate (chronotropy). Additionally, isoproterenol can enhance cardiac conduction through the atrioventricular (AV) node, making it useful in certain cases of bradycardia or heart block.

5. Effects on the bronchial smooth muscle (beta-2 stimulation): Isoproterenol's action on beta-2 receptors in the bronchial smooth muscle causes relaxation and bronchodilation, which can be helpful in managing bronchospasm during the perioperative period.

6. Effects on vascular smooth muscle (beta-2 stimulation): Isoproterenol also acts on beta-2 receptors in the vascular smooth muscle, causing vasodilation. This effect can be useful in specific cases of vasodilatory shock, where increasing vascular tone may be beneficial.

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                                                                                         Key points about Isoproterenol

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• Direct-acting synthetic catecholamine that stimulates both beta 1 and beta 2 adrenergic receptors.

 

• It produces intense stimulation of the heart, increasing heart rate, contractility, and cardiac output.

 

• It vasodilates the arterioles of skeletal muscle (beta 2 effect), resulting in decreased peripheral resistance.

 

• It greatly reduces mean arterial and diastolic blood pressure.

 

• It causes an increase in myocardial oxygen demand.

 

• May cause an increase in blood glucose levels.

 

• Contains sulfites which may provoke an allergic reaction in patients with sulfa allergy.

 

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