This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Hematology and CVS, Subject name: Pharmacology
Clonidine is used as an antihypeensive agent but if used as a fast intravenous injection, it can increase the blood pressure due to: 
Select and explain. 
A. Stimulation of vasomotor center, B. Release of noradrenaline from adrenergic nerve endings, C. Agonistic action on vascular a2 adrenergic receptors, D. Cardiac stimulation
C: Agonistic action on vascular a2 adrenergic receptors
Answer: C: Agonistic action on vascular a2 adrenergic receptors 
Explanation: Alpha 2 receptors are present both presynaptically as well as postsynaptically. Clonidine acts as presynaptic a2 agonist and decreases the central sympathetic outflow. However, it can also act on vascular postsynaptic a2 receptors, leading to vasoconstriction and increase in blood pressure. Chances of this reaction is more when clonidine is administered by quick i.v. injection.