Tolazoline is a competitive α1- and α2-adrenergic receptor antagonist (pKis ~6.5) well-known for its peripheral vasodilator effects in animal models. It also is reported to produce histamine-like effects that are sensitive to histamine H2-receptor antagonism in whole animals and a variety of isolated tissues. Certain α2-adrenergic receptor antagonists, including tolazoline, are most commonly used in veterinary medicine as reversal agents for the sedative effects of α2-adrenergic receptor agonists such as xylazine .
