Which ONE of the following is TRUE about a competitive antagonism ?
**Core Concept**
Competitive antagonism is a type of pharmacological antagonism where an antagonist binds to a receptor, blocking the action of an agonist without altering the receptor's affinity for the agonist. This results in a decrease in the agonist's effect, but the receptor's intrinsic activity remains unchanged.
**Why the Correct Answer is Right**
In competitive antagonism, the antagonist and agonist compete for the same binding site on the receptor. As the antagonist occupies the binding site, it reduces the availability of the site for the agonist, leading to a decrease in the agonist's effect. This type of antagonism is reversible and can be overcome by increasing the concentration of the agonist. The antagonist does not alter the receptor's intrinsic activity, and its effect is specific to the agonist.
**Why Each Wrong Option is Incorrect**
**Option A:** Non-competitive antagonism is incorrect because in non-competitive antagonism, the antagonist binds to a different site on the receptor, reducing its intrinsic activity, and cannot be overcome by increasing the agonist concentration.
**Option B:** Agonist is incorrect because an agonist increases the receptor's activity, not decreases it.
**Option C:** Inverse agonist is incorrect because an inverse agonist decreases the receptor's intrinsic activity, which is not the case in competitive antagonism.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that competitive antagonism can be overcome by increasing the dose of the agonist, whereas non-competitive antagonism cannot be overcome by increasing the agonist dose.
**Correct Answer: C. An agonist is a substance that increases the frequency or amplitude of the receptor's response, whereas an antagonist is a substance that decreases the receptor's response.