Takayanagi I, Shiraishi K, Kokubu N
Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Chiba, Japan.
Jpn J Pharmacol. 1992 Jul;59(3):301-5. doi: 10.1254/jjp.59.301.
Rabbit isolated iris dilator strips were contracted by norepinephrine, an alpha 1A- and alpha 1B-nonselective agonist, but not by methoxamine, an alpha 1A-selective agonist. The concentration-response curve for norepinephrine was considerably inhibited by chloroethylclonidine. The pA2 values for WB4101 and 5-methylurapidil were 8.16 +/- 0.09 and 7.84 +/- 0.08 (means +/- S.E. of 8-12 experiments), respectively, and significantly smaller than the values reported in the rat renal artery and thoracic aorta, and rabbit bronchus, where the alpha 1A-subtype is predominant. These results suggest that the rabbit iris dilator contains primarily the alpha 1B-subtype. Clonidine and tizanidine did not contract the rabbit iris dilator but shifted the curve for norepinephrine in a parallel manner, suggesting that they interact with the alpha 1B-subtype and act as competitive antagonists in this muscle. Methoxamine (up to 10(-3) M) had no effect on the contractile response to norepinephrine, suggesting that methoxamine does not interact with the alpha 1B-subtype.
兔离体虹膜开大肌条可被去甲肾上腺素（一种α1A和α1B非选择性激动剂）收缩，但不被甲氧明（一种α1A选择性激动剂）收缩。氯乙可乐定可显著抑制去甲肾上腺素的浓度-反应曲线。WB4101和5-甲基尿嘧啶的pA2值分别为8.16±0.09和7.84±0.08（8 - 12次实验的平均值±标准误），且显著小于在大鼠肾动脉、胸主动脉和兔支气管中报道的值，在这些组织中α1A亚型占主导。这些结果表明兔虹膜开大肌主要含有α1B亚型。可乐定和替扎尼定不会使兔虹膜开大肌收缩，但会使去甲肾上腺素的曲线平行移动，表明它们与α1B亚型相互作用并在该肌肉中作为竞争性拮抗剂起作用。甲氧明（高达10⁻³ M）对去甲肾上腺素的收缩反应无影响，表明甲氧明不与α1B亚型相互作用。
