Vasomotor reversal phenomenon after administration of an a adrenergic blocker is seen with

Rapid i.v. injection of Adr produces a marked increase in both systolic as well as diastolic BP (at high concentration a response predominates and vasoconstriction occurs even in skeletal muscles). The BP returns to normal within a few minutes and a secondary fall in mean BP follows. The mechanism is--rapid uptake and dissipation of Adr - concentration around the receptor is reduced - low concentrations are not able to act on a receptors but continue to act on b2 receptors. When an a blocker has been given, only fall in BP is seen--vasomotor reversal of Dale. Ref:- kd tripathi; pg num:-131