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Related Concept Videos

Adrenergic Agonists: Indirect-Acting Agents01:25

Adrenergic Agonists: Indirect-Acting Agents

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Indirect-acting adrenergic agonists potentiate the effects of endogenous catecholamines through different mechanisms without directly binding to adrenoceptors.
One mechanism involves depleting stored catecholamines by displacing them from synaptic vesicles. These agents, known as "displacers," are transported into vesicles at the expense of noradrenaline. Examples include amphetamine and tyramine, which lack a catechol moiety, resulting in prolonged action, improved oral...
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Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers01:22

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

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Class I antiarrhythmic drugs are used to treat various types of arrhythmias or irregular heart rhythms. These drugs block the sodium (Na+) channels in the cardiac cells, thereby affecting the movement of electrical impulses across the heart. Class I antiarrhythmic drugs are divided into three subgroups: Class IA, Class IB, and Class IC, each with distinct mechanisms of action and effects on the heart.
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
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Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

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Adrenergic stimulation generally impacts cardiac rate and rhythm. Specifically, stimulation of the β-adrenoceptors triggers an increase in intracellular calcium ion influx and pacemaker currents, which may cause arrhythmias. Catecholamines like adrenaline also demonstrate β2-adrenoceptor-mediated hypokalemia, impacting cardiac action potential and disrupting the normal cardiac rhythm. Class II antiarrhythmic drugs are β-adrenoceptor antagonists or β-blockers, which...
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Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

2.9K
Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of...
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Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

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Class IV antiarrhythmic drugs, such as verapamil and diltiazem, block calcium channels. They primarily affect the heart, slowing the conduction in calcium-dependent tissues like the SA and AV nodes. These drugs manage reentrant supraventricular tachycardia (SVT) and reduce ventricular rate in atrial flutter/fibrillation.
Verapamil, a calcium channel blocker, inhibits calcium movement across myocardial cell membranes and vascular smooth muscle. This results in the dilation of coronary and...
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Heart Failure Drugs: Inotropic Agents01:26

Heart Failure Drugs: Inotropic Agents

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Positive inotropic agents are commonly used as the first line of treatment for heart failure. One such agent is digoxin, derived from the genus Digitalis, which has been known for centuries but effectively utilized since 1785. However, these cardiac glycosides can have potentially toxic effects due to their mechanism of action, which involves inhibiting Na+/K+-ATPase and increasing contractility. Digoxin is absorbed orally and distributed in various tissues, including the CNS. It has a long...
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Related Experiment Video

Updated: May 1, 2026

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice
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Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

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Non-receptor-mediated inotropic drugs.

L Storstein1

  • 1Division of Pharmacology and Toxicology, Ullevaal Hospital, University of Oslo, Norway.

European Heart Journal
|June 1, 1988
PubMed
Summary

Researchers are exploring new positive inotropic agents, focusing on phosphodiesterase inhibitors. These drugs, like milrinone, increase intracellular cyclic AMP to enhance heart contraction, offering potential therapeutic benefits with careful consideration of side effects.

Area of Science:

  • Cardiology
  • Pharmacology

Background:

  • Active search for non-glycoside, non-sympathomimetic positive inotropic agents.
  • Phosphodiesterase (PDE) inhibitors increase intracellular cyclic AMP (cAMP) concentration, enhancing myocardial contraction.
  • Methylxanthines show in vitro positive inotropic effects, but in vivo actions are complex.

Purpose of the Study:

  • To review novel phosphodiesterase inhibitors, particularly those targeting PDE-III.
  • To evaluate drugs with combined inotropic and vasodilatory actions.
  • To discuss the clinical relevance of inotropic versus vasodilatory effects and pharmacokinetic profiles.

Main Methods:

  • Review of existing literature on phosphodiesterase inhibitors.
  • Analysis of clinical trial data for drugs like amrinone and milrinone.

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  • Assessment of drug efficacy, side-effect profiles, and pharmacokinetic properties.

    • Main Results:

    • Amrinone is largely withdrawn due to side effects; milrinone shows promise in trials.
    • Sulmazole was withdrawn due to rodent toxicity.
    • New PDE inhibitors are under investigation, with varying therapeutic potentials.

    Conclusions:

    • Milrinone is a well-tolerated PDE inhibitor with promising clinical trial results.
    • The balance between inotropic and vasodilatory effects, sustained clinical benefits, and side-effect profiles are critical for therapeutic success.
    • Further investigation into novel PDE inhibitors is warranted.