Alpha adrenergic receptor antagonists - phentolamine 【Mechanism】 Pentolamine has similar affinity for both and o,receptors.It is a competitive antagonist.It has wide spectrum of pharmacological specificities. Short-term blocker.Alpha adrenergic receptor antagonists -- phentolamine 【 Mechanism 】 Pentolamine has similar affinity for both 1 and 2 receptors. It is a competitive antagonist. It has wide spectrum of pharmacological specificities. Short-term  blocker