Which of the following is a selective Beta 2 antagonist?
**Core Concept**
Beta 2 adrenergic receptors are a subtype of adrenergic receptors that are primarily found in the smooth muscle of the bronchi, uterus, and blood vessels. Selective beta 2 antagonists are used to treat conditions such as asthma and bronchospasm by blocking the action of epinephrine on these receptors.
**Why the Correct Answer is Right**
The correct answer is **C. ICI-118,551**. ICI-118,551 is a selective beta 2 antagonist that has high affinity for beta 2 adrenergic receptors and is used in research and clinical settings to study the effects of beta 2 receptor blockade. It works by competitively inhibiting the binding of epinephrine to beta 2 receptors, thereby reducing bronchodilation and vasodilation.
**Why Each Wrong Option is Incorrect**
* **Option A:** **Propranolol** is a non-selective beta blocker that blocks both beta 1 and beta 2 adrenergic receptors, making it an incorrect choice.
* **Option B:** **Atenolol** is a selective beta 1 antagonist that is primarily used to treat hypertension and angina, making it an incorrect choice.
* **Option D:** **Terbutaline** is a selective beta 2 agonist that is used to treat asthma and bronchospasm, making it an incorrect choice.
**Clinical Pearl / High-Yield Fact**
Beta 2 antagonists can cause bronchoconstriction and should be used with caution in patients with asthma or chronic obstructive pulmonary disease (COPD).
**Correct Answer:** C. ICI-118,551