Differences in alpha 1-adrenoceptor mechanisms for phenylephrine and tizanidine in rabbit thoracic aorta and common iliac artery.

Based on affinity for WB4101 and susceptibility to chloroethylclonidine, we evaluated the subtype of alpha 1-adrenoceptors activated by phenylephrine (a full agonist) and tizanidine (a partial agonist). The rabbit thoracic aorta and common iliac artery contain both alpha 1A- and alpha 1B-adrenoceptors, but the alpha 1B-subtype may be more predominantly in the common iliac artery than in the thoracic aorta. In rabbit thoracic aorta and common iliac artery, phenylephrine induced contraction through both alpha 1A- and alpha 1B-subtypes and tizanidine through only the alpha 1A-subtype. The subtype activated by phenylephrine may be partly different from that activated by tizanidine in the preparations used herein.