Ans: D. Action on presynaptic alpha-receptors(Ref: Goodman Gilman 12/e p209, 302, 308)Activation of presynaptic ?2 receptors inhibits the release of NE and other co-transmitters front peripheral sympathetic nerve endings.Activation of ?2 receptors in the pontomedullary region of the CNS inhibits sympathetic nervous system activity and leads to a full in blood pressure.Action on presynaptic alpha-receptors (a2 receptors) is not helpful in management of anaphylactic shock.