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Adrenergic Agonists: Indirect-Acting Agents

Adrenergic Agonists: Indirect-Acting Agents

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 bioavailability, and...

Adrenergic Agonists: Direct-Acting Agents

Adrenergic Agonists: Direct-Acting Agents

Drugs that mimic the action of endogenous catecholamines like noradrenaline and adrenaline are called adrenergic agonists or sympathomimetics. Based on their mechanism of action, sympathomimetics can be classified as direct-, indirect-, or mixed-acting sympathomimetics. Direct-acting adrenergic agonists activate adrenoceptors without affecting presynaptic neurons, making them independent of neuronal catecholamine-depleting agents like reserpine and guanethidine.
These agents can be classified...

Adrenergic Agonists: Mixed-Action Agents

Adrenergic Agonists: Mixed-Action Agents

Mixed-action adrenergic agonists, like ephedrine and pseudoephedrine, directly and indirectly affect adrenergic receptors. These agents stimulate adrenoceptors and indirectly release stored neurotransmitters, amplifying the adrenergic response.
Ephedrine and pseudoephedrine lack a catecholamine group, making them less susceptible to degradation by metabolic enzymes. They have increased oral bioavailability and lipophilicity, resulting in a longer duration of action. Their response is reduced by...

Adrenergic Agonists: Chemistry and Structure-Activity Relationship

Adrenergic Agonists: Chemistry and Structure-Activity Relationship

Adrenergic agonists' structure-activity relationship (SAR) determines their selectivity and efficacy. These agonists comprise a phenylethylamine moiety with an aromatic ring and an ethylamine side chain.
Aromatic ring substitutions: Substituting the aromatic ring with –OH groups at positions 3 and 4 yields catecholamines (e.g., epinephrine), which have a high affinity for adrenoceptors. Hydrogen bonding between –OH groups and receptors enhances adrenergic activity.
Separation of the aromatic...

Indirect-Acting Cholinergic Agonists: Mechanism of Action

Indirect-Acting Cholinergic Agonists: Mechanism of Action

Indirect-acting cholinergic agonists work by interacting with an enzyme called acetylcholinesterase (AChE) in the synaptic cleft. They can be reversible or irreversible inhibitors and have different effects on the enzyme.
Reversible inhibitors like edrophonium bind to a specific part of the enzyme called the anionic catalytic site. They form noncovalent bonds, which means they are not strongly attached to the enzyme. This creates a temporary and less stable enzyme–inhibitor complex, leading to...

Direct-Acting Cholinergic Agonists: Pharmacological Actions

Direct-Acting Cholinergic Agonists: Pharmacological Actions

Direct-acting cholinergic agonists exert their pharmacological actions by mimicking the effects of acetylcholine on postsynaptic muscarinic receptors to generate parasympathetic responses. These agents elicit a range of physiological responses, including cardiovascular effects. For example, activation of muscarinic receptors induces bradycardia, decreased cardiac output, reduced peripheral resistance, and consequent hypotension. In the eye, stimulation of M3 receptors leads to smooth muscle...

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Related Experiment Video

Updated: May 17, 2026

Drug-induced Sensitization of Adenylyl Cyclase: Assay Streamlining and Miniaturization for Small Molecule and siRNA Screening Applications

Drug-induced Sensitization of Adenylyl Cyclase: Assay Streamlining and Miniaturization for Small Molecule and siRNA Screening Applications

Published on: January 27, 2014

Behavioral involvement of imidazoline system.

M Nechifor¹, Diana Ciubotariu

¹Pharmacology Department, Faculty of Dental Medicine, University of Medicine and Pharmacy "Grigore T. Popa"--Iaşi.

Revista Medico-Chirurgicala a Societatii De Medici Si Naturalisti Din Iasi

|October 20, 2012

Summary

The imidazoline system, involving I1, I2, and I3 receptors, modulates behavior. Selective agonists targeting these receptors show promise for treating behavioral disorders like anxiety and stress.

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Assessment of Social Interaction Behaviors

Assessment of Social Interaction Behaviors

Published on: February 25, 2011

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Last Updated: May 17, 2026

Drug-induced Sensitization of Adenylyl Cyclase: Assay Streamlining and Miniaturization for Small Molecule and siRNA Screening Applications

Drug-induced Sensitization of Adenylyl Cyclase: Assay Streamlining and Miniaturization for Small Molecule and siRNA Screening Applications

Published on: January 27, 2014

Assessment of Social Interaction Behaviors

Assessment of Social Interaction Behaviors

Published on: February 25, 2011

Area of Science:

Neuroscience
Pharmacology

Background:

The imidazoline system comprises I1, I2, and I3 receptors with endogenous ligands.
This system plays a crucial role in modulating various behaviors.

Purpose of the Study:

To explore the role of the imidazoline system in behavioral modulation.
To investigate the therapeutic potential of selective imidazoline receptor agonists for behavioral disorders.

Main Methods:

Review of existing data on imidazoline receptor function and behavior.
Analysis of the effects of I1 and I2 receptor modulation on behavioral components.

Main Results:

I1 and I2 receptors differentially affect behavioral components including suicidal behavior, stress, anxiety, and food intake.
Imidazoline receptor ligands also interact with alpha-adrenergic receptors and monoamine oxidase (MAO).

Conclusions:

Selective I1 and I2 agonists represent potential therapeutic agents for behavioral disorders.
The interaction with other systems like adrenergic and MAO broadens the application of imidazoline receptor modulators.