B

After α1-adrenoceptors are blocked, administration of adrenaline (or another agonist that can still act on β2 receptors) produces a fall—not a rise—in blood pressure because the unopposed β2-mediated vasodilation dominates; this classic “vasomotor reversal of Dale” therefore requires α1 blockade followed by β2 stimulation [McPherson et al., 1981, PMID 6167804].