Which of the following is a selective alpha 2 agonist
**Core Concept**
Selective alpha 2 agonists are a class of medications that act on the alpha 2 adrenergic receptors, which are a subtype of adrenergic receptors. These receptors are involved in various physiological processes, including vasoconstriction, sedation, and analgesia. Selective alpha 2 agonists are used to treat conditions such as hypertension, anxiety, and pain.
**Why the Correct Answer is Right**
The correct answer is a selective alpha 2 agonist because it activates the alpha 2 adrenergic receptors, leading to an increase in the activity of the enzyme **guanylate cyclase**. This results in an increase in the production of cyclic guanosine monophosphate (cGMP), which causes vasodilation and a decrease in blood pressure. The selective alpha 2 agonist also has a sedative effect by stimulating the release of **gamma-aminobutyric acid (GABA)**, an inhibitory neurotransmitter.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is a non-selective alpha 2 agonist, which means it also activates other adrenergic receptors, leading to unwanted side effects such as vasoconstriction and increased heart rate.
**Option B:** This option is incorrect because it is a selective alpha 1 agonist, which is used to treat conditions such as benign prostatic hyperplasia and hypertension, but it does not have a sedative effect.
**Option C:** This option is incorrect because it is an antagonist of the alpha 2 adrenergic receptor, which would lead to an increase in blood pressure and an increase in the release of norepinephrine.
**Clinical Pearl / High-Yield Fact**
Selective alpha 2 agonists are useful in treating hypertension and anxiety disorders because they have a favorable side effect profile compared to non-selective alpha 2 agonists. They can also be used as adjunctive therapy in the treatment of pain.
**Correct Answer: C. Clonidine**