Pharmacological and Electrophysiological Discrimination of Contractile Responses to Selective α1- and α2-Adrenoceptor Agonists in Rat Tail Artery

[摘要] References(39)Cited-By(19)Pharmacological and electrophysiological properties of postsynaptic α-adrenoceptor subtypes in rat tail artery were compared using selective α1 and α2-adrenoceptor agonists. Five α-adrenoceptor agonists contracted the tail artery with the following order of maximal effects: norepinephrine (α1 and α2)>methoxamine (α1)=phenylephrine (α1)>>clonidine (α2)>UK-14, 304 (α2). Phenoxybenzamine greatly diminished contractions induced by methoxamine and phenylephrine, but had little effect on responses to UK-14, 304. Idazoxan antagonized more potently against UK-14, 304 than against methoxamine. These results suggest the heterogeneity of postsynaptic α-adrenoceptors in the rat tail artery. Furthermore, responses to methoxamine and phenylephrine 1) had faster onsets and 2) were more resistant to Ca2+ entry blockers, nicardipine and diltiazem, and a promotor, Bay K 8644, or decreasing of extracellular Ca2+ and 3) were more sensitive to a calmodulin antagonist, W-7, than the responses to UK-14, 304 and clonidine. Both methoxamine and UK-14, 304 depolarized the membrane but methoxamine produced stronger depolarization than UK-14, 304. Therefore, the high sensitivity of α2-adrenoceptor agonists-induced responses to Ca2+ entry blockers and promotors cannot be accounted for solely by membrane depolarization. These results may indicate the differences in the Ca2+ movement for the contractions produced by α1- and α2-adrenoceptor agonists.

[学科分类] 药理学