Antagonism | Types of Antagonism

Antagonism:

Antagonism refers to the interaction between two substances or organisms in which one inhibits or counteracts the action of the other. For example, certain medications may work by antagonizing the effects of certain neurotransmitters or hormones in the body.

Types of Antagonism:

There are three types of antagonism:

1. Pharmacological antagonism
2. Physiological antagonism
3. Chemical antagonism

Pharmacological Antagonism

Antagonists bind to receptors preventing an Agonist from interacting with its receptors to produce an effect.

Pharmacological antagonism refers to the interaction between two substances, where one substance (the antagonist) inhibits or counteracts the effect of another substance (the agonist) in the body.

Pharmacological antagonism is an important concept in pharmacology, as it can be used to develop drugs that can be used to treat various medical conditions. For example, beta-blockers are a type of pharmacological antagonist that can be used to treat high blood pressure, by blocking the effects of adrenaline on the heart and blood vessels.

Types of pharmacological antagonism:

There are two types of pharmacological antagonism.

1. Competitive antagonism / reversible antagonism
2. Non competitive antagonism / irreversible antagonism

Competitive antagonism / reversible antagonism:

Antagonist competes with agonist in reversible fashion for the same receptor site. High antagonist concentration prevent agonist response completely but sufficiently high concentration of agonist can completely overcome the effect of antagonist. For example propranolol at beta adrenoceptors.

In competitive antagonism, the antagonist does not activate the receptor, but instead blocks the action of the agonist by occupying the receptor site. This reduces the effectiveness of the agonist and decreases its biological response.

Examples of competitive antagonism include the use of naloxone to reverse the effects of opioids such as morphine, or the use of beta-blockers to block the effects of adrenaline on the heart and blood vessels.

Non competitive antagonism / irreversible antagonism:

Antagonist bind irreversibly to receptor site and this antagonism cannot be overcome no matter how much agonist is given , for example phenoxybenzamine at alpha adrenoceptors.

Unlike competitive antagonism, non-competitive antagonists can bind to the receptor even in the absence of the agonist. This type of antagonism usually results in a reduction of the maximal response of the agonist, rather than a shift in the agonist’s potency.

Examples of non-competitive antagonism include the use of ketamine to block the N-methyl-D-aspartate (NMDA) receptor, which is involved in pain perception, and the use of phenoxybenzamine to block the alpha-adrenergic receptors in blood vessels, which leads to dilation of blood vessels.

Physiological antagonism:

In this, antagonist act on a separate receptor and brings about effects opposite to that produced by agonist. A familiar example of a physiological antagonist in the antagonism of the bronchoconstrictor action of histamine (mediated at histamine receptors) by Epinephrine bronchodilator action (mediated at beta adrenoceptors). Similarly Glucagon (acting at Glucagon receptor) can antagonise the cardiac effects of an overdose of Propranolol (acting at beta adrenoceptors).

In physiological antagonism, the antagonist produces a different effect from the agonist, which counteracts the agonist’s effect. For example, an agonist that causes constriction of blood vessels may be counteracted by an antagonist that causes dilation of blood vessels, such as nitroglycerin, which is used to treat angina.

example of physiological antagonism is the use of naloxone to treat respiratory depression caused by opioid overdose. In this case, naloxone blocks the effects of opioids by binding to opioid receptors in the brain, but it does not produce the same effects as opioids. Instead, it produces an opposite effect by stimulating breathing and reversing the respiratory depression caused by the opioids.

Chemical antagonism:

In this, two drugs combined with one another to form an inactive compound without involving any receptor. For example, protamine sulphate is a chemical antagonist for heparin. Protamibe is a basic (positively charged) protein that binds to the acidic heparin (negatively charged), rapidly preventing its therapeutic as well as to the toxic effects.

In chemical antagonism, the antagonist and agonist do not bind to the same receptor, but instead interact with each other directly. This interaction can result in a chemical reaction that renders the agonist inactive or eliminates it from the body.

Example of chemical antagonism is the use of chelating agents to bind and remove heavy metals from the body. Heavy metals can be toxic to the body, but chelating agents can form a complex with the metal ions, rendering them inactive and allowing them to be excreted from the body.

Another example of chemical antagonism is the use of antacids to neutralize the effects of stomach acid. Antacids work by chemically reacting with the acid to form a neutral substance, which can reduce the symptoms of acid reflux and heartburn.

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What is antagonism?

Types of Antagonism

There are how many types of antagonism?

What is antagonism?

What is pharmacological antagonism?

What is physiological antagonism?

What is antagonism?

What is chemical antagonism?

Types of pharmacological antagonism

What is antagonism?

There are how many types of pharmacological antagonism

What is competitive antagonism?

What is reversible antagonism?

What is antagonism?

What is non competitive antagonism?

What is irreversible antagonism?