Bond R A, Clarke D E
Br J Pharmacol. 1987 Jul;91(3):683-6. doi: 10.1111/j.1476-5381.1987.tb11262.x.
The hypothesis that beta-adrenoceptor agonism might explain a reported lack of competitive antagonism between alpha 2-adrenoceptor antagonists and agonists of the phenylethylamine class was tested in the electrically field stimulated ileum of the guinea-pig. The beta-adrenoceptor agonist, isoprenaline, was used as the phenylethylamine and inhibition of 'twitch' response evoked by cholinergic stimulation was measured. In the presence of idazoxan (3 microM), to block inhibitory alpha 2-adrenoceptors, propranolol (0.1 to 5.0 microM) failed to act competitively toward isoprenaline. Isoprenaline responses totally resistant to inhibition by propranolol were obtained. As inhibitory alpha 1-adrenoceptors are absent from guinea-pig ileum, a recognition site distinct from the currently defined alpha- and beta-adrenoceptors is postulated. Agonism by phenylethylamine based agonists at this site may explain their inability to act competitively with alpha- and beta-adrenoceptor antagonists.
β-肾上腺素能受体激动作用或许可以解释α2-肾上腺素能受体拮抗剂与苯乙胺类激动剂之间缺乏竞争性拮抗作用这一现象，这一假说在豚鼠电场刺激回肠中得到了验证。使用β-肾上腺素能受体激动剂异丙肾上腺素作为苯乙胺，并测定胆碱能刺激诱发的“抽搐”反应的抑制情况。在存在咪唑克生（3微摩尔）以阻断抑制性α2-肾上腺素能受体的情况下，普萘洛尔（0.1至5.0微摩尔）对异丙肾上腺素未表现出竞争性作用。获得了对普萘洛尔抑制作用完全抵抗的异丙肾上腺素反应。由于豚鼠回肠中不存在抑制性α1-肾上腺素能受体，因此推测存在一个与目前定义的α-和β-肾上腺素能受体不同的识别位点。基于苯乙胺的激动剂在此位点的激动作用或许可以解释它们无法与α-和β-肾上腺素能受体拮抗剂产生竞争性作用的原因。
