Antagonists do not cause biological effects on their own after binding to the receptor, but block the receptor agonist-mediated effects. Antagonists can be divided into two classes based on whether they reversibly compete with agonists bound to receptors.
Classify：
From the perspective of distinguishing competitive antagonists from non-competitive antagonists, the effects of competitive antagonists can be countered by increasing agonist concentrations, while the effects of non-competitive antagonists cannot be antagonized by increasing agonist antagonists. Competitive antagonists can increase ED50 values, whereas non-competitive antagonists cannot.
1.Competitive antagonists
The drug has an affinity for the receptor but does not produce a receptor agonist effect, which prevents the agonist from binding to the receptor. Increasing the concentration of a reversible competitive antagonist while the agonist concentration is fixed can gradually inhibit the agonist-generated response. At a high concentration, the antagonist can completely prevent the reaction from occurring. Conversely, a sufficiently high concentration of agonists can remove the action of a certain concentration of antagonists and still achieve maximum effect Emax. Because the antagonist is competitive, the presence of the antagonist requires an increase in the concentration of the agonist to reach a specific response height, which shifts the agonist concentration-effect curve parallel to the right. There are also antagonists that inhibit the intrinsic activity of the receptor in addition to preventing the agonist from binding to the receptor.
From a therapological point of view, the significance of this competitive antagonist is as follows: (1) The degree of inhibition of competitive antagonists depends on the concentration of antagonists. Adjusting the dosage based on the concentration of the drug entering the body makes sense to produce the desired therapeutic effect. (2) The clinical response to an antagonist depends on the concentration of the agonist that binds to the receptor.
2.Non-competitive antagonists
A drug that binds to a receptor protein at a site different from the agonist’s binding site and prevents the agonist from causing receptor activation. On the dose-response graph, non-competitive antagonism usually reduces the slope and height of the response curve, and also causes a certain degree of rightward shift of the response curve. Drugs that bind to receptor proteins that are distinct from agonist binding sites are often referred to as allosteric modulators. Allosteric modulators are able to alter receptor function but not to agonize receptors, as is benzodiazepines.
Pharmacology：
1.M receptor antagonist: scopolamine
The drug is a belladonna alkaloid, which has a stronger and longer-lasting effect on the central nervous system than atropine. It can cause central nervous system depression at therapeutic doses, and has obvious sedative effects, manifested as drowsiness, forgetfulness, fatigue, and shortened REM sleep, but at high doses, it produces stimulant effects. In addition, this crystal can block short-term memory and is also often used during anesthesia. This drug also has a central anticholinergic effect, and it also has a certain effect on Parkinson’s disease, which can improve its symptoms such as tremor, salivation and muscle rigidity.
2.N-receptor antagonist: succinylcholine
It is composed of succinic acid and two molecules of choline, which is easily destroyed in alkaline solution, and if mixed with sodium thiopental, the activity decreases quickly.
【Pharmacological effects】The relaxation effect of skeletal muscle is fast and short-lived, and it is easy to control. After a single intravenous injection of 10-30 mg, uncoordinated fasciculations can be seen within 20 seconds. After 1 minute, it will turn to relaxation, reach its peak in 2 minutes, and disappear in 5 minutes. The muscle relaxation effect starts from the neck muscles and gradually spreads to the shoulder blades, limbs and abdomen, with the neck and limb muscles being the most obvious, followed by the face, tongue, throat and masticatory muscles, and the weakest effect on the respiratory muscles, but the effect on the laryngeal and tracheal smooth muscles is stronger.
【Clinical application】The relaxation effect of skeletal muscle of this product is fast and short-lived, and intravenous administration is suitable for short-term operations such as endotracheal intubation, tracheoscopy, and esophagoscopy. It can also be adjuvanted intravenously as an adjunct to general anesthesia, reducing the amount of general anesthesia, and the skeletal muscles are completely relaxed under shallow anesthesia, so that the operation can be carried out smoothly for a long time. The drug can cause a strong feeling of asphyxia, so it is contraindicated in awake patients, and succinylcholine can be given after intravenous anesthesia with sodium thiopental. In addition, the drug can also be used in electroconvulsive therapy. Due to the large individual differences of the drug, the speed of administration needs to be adjusted according to the effect to obtain a satisfactory effect.
About BaiLun Biotechnology Co., Ltd：
BaiLun Biotechnology Co., Ltd. stands as a leading supplier and premier technical service provider, specializing in the provision of comprehensive bioreactor systems and advanced control solutions. Our extensive product line encompasses a wide array of offerings, ranging from bioreactors (fermenters) to animal cell bioreactors, biological shakers, and control systems tailored for bioprocessing applications. With a capacity spanning from 0.1L to 1000KL, we are committed to fostering the growth of China’s bioreactor industry on a global scale.
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