A drug 'X' is an a adrenergic blocker but paradoxically produces vasoconstriction. 'X' is:
Ergot alkaloids are the alpha-blockers that can cause vasoconstriction. The vasoconstriction caused by ergot alkaloids is due to stimulation of serotonin receptors. Ergotamine It acts as a paial agonist and antagonist at a adrenergic and all subtypes of 5-HT1 and 5-HT2 receptors, but does not interact with 5-HT3 or dopamine receptors. Sustained vasoconstriction , visceral smooth muscle contraction, vasomotor centre depression are produced, and the action of NA and 5-HT on smooth muscles is antagonized. It is a potent emetic and oxytocic. At high doses CNS stimulation and paresthesias can be seen.
Phenoxybenzamine
Ergotamine
Prazosin receptors
Tolazoline
Sympathetic System