Regardless, a beta-1 receptor selective beta blocker such as atenolol must never be used in the presence of a pheochromocytoma due to the risk of such a treatment leading to unopposed alpha agonism and, thus, severe and potentially refractory hypertension.
Regardless, a nonselective beta-adrenergic receptor blocker such as propranolol must never be used in the presence of a pheochromocytoma. The mechanism for β-adrenoceptor blocker-associated adverse events is generally ascribed to inhibition of β2-adrenoceptor-mediated vasodilatation, leaving α1-adrenoceptor-mediated vasoconstrictor responses to catecholamines unopposed and, thus, severe and potentially refractory hypertension.