The effect of several α-adrenoceptor antagonists on the response to histamine in various tissues

Abstract

The effect of various α-receptor antagonists on the histamine-induced response of guinea pig ileum, guinea pig heart, and rabbit portal vein have been studied. In guinea pig ileum, an H₁ receptor system, phenoxybenzamine and dibozane are effective antagonists, phentolamine is a weak antagonist, azapetine is without antagonist effect, and tolazoline is a weak agonist. In the H₂ system of guinea pig right ventricle, phentolamine and azapetine are antagonists, phenoxybenzamine and dibozane are inactive, and tolazoline is an agonist. All antagonists except tolazoline block the histamine response in portal vein which is believed to be mediated by a receptor of low selectivity. Tolazoline is an agonist in portal vein.