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Cholinergic Antagonists: Pharmacokinetics

Cholinergic Antagonists: Pharmacokinetics

Cholinergic antagonists—such as antimuscarinics—are available in oral, topical, ocular, parenteral, and inhalational formulations. Most antimuscarinics are oral formulations, while scopolamine is available as a topical patch, and ipratropium and tiotropium are available as inhalation aerosols or powders. Atropine, tropicamide, and cyclopentolate are topically instilled in the eye. Most antimuscarinics are lipid-soluble and readily absorbed from the gastrointestinal tract and the conjunctiva.

Direct-Acting Cholinergic Agonists: Pharmacokinetics

Direct-Acting Cholinergic Agonists: Pharmacokinetics

Direct-acting cholinergic agonists, such as synthetic choline esters and naturally occurring alkaloids, exert their effects by enhancing the actions of acetylcholine and stimulating the parasympathetic nervous system. Synthetic choline esters share structural similarities with acetylcholine. For example, they have a positively charged quaternary ammonium or onium group, contributing to their hydrophilic characteristics. As a result, they are poorly absorbed in the body through oral...

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: Chemistry and Structure-Activity Relationship

Direct-Acting Cholinergic Agonists: Chemistry and Structure-Activity Relationship

Cholinergic agonists or cholinomimetics mimic the action of acetylcholine to stimulate the parasympathetic nervous system. They are categorized into direct-acting and indirect-acting agents. The direct-acting cholinergic drugs induce the parasympathetic response by directly binding to the muscarinic or nicotine receptors. In comparison, the indirect-acting cholinergic drugs prevent acetylcholine hydrolysis, indirectly contributing to the extended parasympathetic response.
The direct-acting...

Indirect-Acting Cholinergic Agonists: Chemistry and Structure-Activity Relationship

Indirect-Acting Cholinergic Agonists: Chemistry and Structure-Activity Relationship

Indirect-acting cholinergic agonists are agents that interact with the acetylcholinesterase enzyme in the synaptic cleft, preventing the breakdown of acetylcholine into choline and acetate. Consequently, the concentration of acetylcholine in the synaptic cleft increases. These agonists can be classified into reversible and irreversible inhibitors based on their duration of action.
Reversible inhibitors display short to medium durations of action. Short-acting agents include simple alcohols with...

Cholinergic Antagonists: Chemistry and Structure-Activity Relationship

Cholinergic Antagonists: Chemistry and Structure-Activity Relationship

Cholinergic antagonists bind to cholinergic receptors and limit the effects of acetylcholine and other cholinergic agonists. Based on the specific cholinergic receptor affinity, these antagonists are classified as muscarinic or nicotinic. Anticholinergics interrupt parasympathetic innervations while sympathetic innervations remain uninterrupted. Muscarinic antagonists are also called 'muscarinic antagonists', 'antimuscarinics', or 'parasympatholytics'. Nicotinic antagonists are called...

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Related Experiment Video

Updated: Jun 18, 2026

An Efficient and Rapid HPLC-QQQ-MS Method for the Quantitation of Tropane Alkaloids in Medicinal Plants

An Efficient and Rapid HPLC-QQQ-MS Method for the Quantitation of Tropane Alkaloids in Medicinal Plants

Published on: June 12, 2026

Quassinoids from Eurycoma longifolia.

Katsunori Miyake¹, Yasuhiro Tezuka, Suresh Awale

¹Institute of Natural Medicine, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan.

Journal of Natural Products

|November 19, 2009

Summary

Ten new quassinoids were isolated from Eurycoma longifolia stems, with some exhibiting novel structural features. Several compounds demonstrated potent cytotoxicity against HT-1080 fibrosarcoma cells.

Related Experiment Videos

Last Updated: Jun 18, 2026

An Efficient and Rapid HPLC-QQQ-MS Method for the Quantitation of Tropane Alkaloids in Medicinal Plants

An Efficient and Rapid HPLC-QQQ-MS Method for the Quantitation of Tropane Alkaloids in Medicinal Plants

Published on: June 12, 2026

Area of Science:

Natural Product Chemistry
Medicinal Chemistry
Pharmacology

Background:

Eurycoma longifolia is a plant traditionally used for medicinal purposes.
Quassinoids are a class of compounds with diverse biological activities.
Investigating the chemical constituents of Eurycoma longifolia can lead to the discovery of new therapeutic agents.

Purpose of the Study:

To isolate and characterize new quassinoids from Eurycoma longifolia stems.
To evaluate the cytotoxicity of isolated compounds against the HT-1080 human fibrosarcoma cell line.

Main Methods:

Isolation of compounds using chromatographic techniques.
Structure elucidation of new compounds using spectroscopic methods (e.g., NMR, MS).
Cytotoxicity assays using the HT-1080 cell line.

Main Results:

Ten new quassinoids (1-10) and 14 known compounds were isolated.
Novel structural features were identified in compounds 1-10, including a unique skeleton and previously unobserved functional groups.
Compounds 11, 23, and 24 exhibited potent cytotoxicity against HT-1080 cells with IC50 values ranging from 0.93 to 1.1 µM.

Conclusions:

The chemical investigation of Eurycoma longifolia yielded structurally diverse quassinoids, including novel compounds.
Certain isolated quassinoids possess significant cytotoxic activity, suggesting potential as anticancer agents.
Further research into these compounds may lead to the development of new cancer therapies.