Evidence in favour of a selective alpha 1-adrenoceptor blocking action of WB 4101 in vivo.

The alpha-adrenoceptor blocking potency of WB 4101 at alpha 1- and alpha 2-adrenoceptors has been investigated in pithed rats. WB 4101 was approximately 97 times more potent at antagonizing the vasopressor responses produced by the selective alpha 1-adrenoceptor agonist phenylephrine, than those produced by the selective alpha 2-adrenoceptor agonist M-7. A dose of WB 4101 (3 mg/kg) that caused extensive blockade of vascular alpha 1-adrenoceptors, but little or no blockade of vascular alpha 2-adrenoceptors, exerted no significant blockade of the presynaptic alpha 2-adrenoceptors in the rat heart. The results support the view that WB 4101 is a highly selective antagonist at alpha 1-adrenoceptors in vivo.