Which of the following drugs shows the phenomenon of vasomotor reversal of Dale after administration of an α adrenergic blocker ?
**Core Concept**
The phenomenon of vasomotor reversal of Dale refers to an increase in sympathetic outflow to blood vessels after administration of an α-adrenergic blocker, leading to vasoconstriction. This occurs due to the removal of α-adrenergic receptor-mediated inhibition on sympathetic neurons.
**Why the Correct Answer is Right**
When α-adrenergic receptors are blocked, the usual α-adrenergic mediated vasoconstriction is lost. However, the sympathetic nervous system still exerts its influence on the blood vessels through β-adrenergic receptors, leading to vasodilation. But, in the presence of α-adrenergic blockers, the sympathetic outflow to the blood vessels increases, resulting in vasoconstriction due to the unopposed action of sympathetic nerves on the blood vessels. This phenomenon is observed with drugs like clonidine, which is a centrally acting α-2 agonist.
**Why Each Wrong Option is Incorrect**
* **Option B:** This option is incorrect because it does not accurately describe the phenomenon of vasomotor reversal of Dale.
* **Option C:** This option is incorrect because it is not related to the phenomenon of vasomotor reversal of Dale.
* **Option D:** This option is incorrect because it is not a correct description of the phenomenon of vasomotor reversal of Dale.
**Clinical Pearl / High-Yield Fact**
The phenomenon of vasomotor reversal of Dale is an important concept in pharmacology and physiology, and understanding it can help in the management of hypertension and other cardiovascular diseases.
**Correct Answer: C. Clonidine**