Moura E, Afonso J, Hein L, Vieira-Coelho M A
Institute of Pharmacology and Therapeutics, Faculty of Medicine, University of Porto, Alameda Prof. Hernani Monteiro, Porto, Portugal.
Br J Pharmacol. 2006 Dec;149(8):1049-58. doi: 10.1038/sj.bjp.0706950. Epub 2006 Oct 30.
This study was carried out to elucidate which alpha(2)-adrenoceptor subtypes mediated the inhibition of noradrenaline and adrenaline release from the adrenal medulla of mice.
Isolated adrenal medullae from wild-type and alpha(2A), alpha(2B) and alpha(2C)-adrenoceptor knockout (KO) mice were placed in superfusion chambers. Catecholamine overflow was evoked by 1,1-dimethyl-4-phenylpiperazinium (500 microM) in absence or in presence of the alpha(2)-adrenoceptor agonist medetomidine. The effect of medetomidine was tested in presence of the alpha-adrenoceptor antagonists rauwolscine, WB 4101, spiroxatrine, phentolamine and prazosin.
In wild-type mice, medetomidine reduced noradrenaline and adrenaline overflow in a concentration-dependent manner (EC(50) in nM: 1.54 and 1.92; E(max) in % of inhibition: 91 and 94, for noradrenaline and adrenaline, respectively). The pK (D) values of the antagonists for noradrenaline overflow did not correlate with pK(D) values at alpha(2A), alpha(2B), or alpha(2C) binding sites. The pK (D) values of the antagonists for adrenaline overflow correlated positively with pK(D) values at alpha(2C) binding sites (opossum kidney cells). The effect of medetomidine (100 nM) on noradrenaline overflow was significantly reduced in all three alpha(2)KO mice (57, 54, 44 % inhibition, for alpha(2A), alpha(2B), and alpha(2C), respectively), whereas the effect of medetomidine on adrenaline overflow was greatly reduced in alpha(2C)KO mice (14 % inhibition).
In the adrenal medulla of mice, all three alpha(2)-adrenoceptor subtypes (alpha(2A), alpha(2B), and alpha(2C)) play an equal role in the inhibition of noradrenaline overflow, whereas the alpha(2C)-adrenoceptor is the predominant alpha(2)-adrenoceptor subtype involved in the inhibitory mechanism controlling adrenaline overflow.
开展本研究以阐明哪种α₂ - 肾上腺素能受体亚型介导了对小鼠肾上腺髓质去甲肾上腺素和肾上腺素释放的抑制作用。
将来自野生型以及α₂A、α₂B和α₂C - 肾上腺素能受体基因敲除（KO）小鼠的离体肾上腺髓质置于灌流小室中。在不存在或存在α₂ - 肾上腺素能受体激动剂美托咪定的情况下，用1,1 - 二甲基 - 4 - 苯基哌嗪鎓（500微摩尔）诱发儿茶酚胺溢出。在存在α - 肾上腺素能受体拮抗剂萝芙辛、WB 4101、螺沙群、酚妥拉明和哌唑嗪的情况下测试美托咪定的作用。
在野生型小鼠中，美托咪定以浓度依赖性方式降低去甲肾上腺素和肾上腺素溢出（去甲肾上腺素和肾上腺素的半数有效浓度（EC₅₀，单位为纳摩尔）分别为1.54和1.92；抑制率的最大效应（Eₘₐₓ，单位为%）分别为91和94）。拮抗剂对去甲肾上腺素溢出的解离常数（pK (D)）值与α₂A、α₂B或α₂C结合位点的pK (D)值不相关。拮抗剂对肾上腺素溢出的pK (D)值与α₂C结合位点（负鼠肾细胞）的pK (D)值呈正相关。在所有三种α₂基因敲除小鼠中，美托咪定（100纳摩尔）对去甲肾上腺素溢出的作用均显著降低（α₂A、α₂B和α₂C基因敲除小鼠的抑制率分别为57%、54%和44%），而美托咪定对肾上腺素溢出的作用在α₂C基因敲除小鼠中大幅降低（抑制率为14%）。
在小鼠肾上腺髓质中，所有三种α₂ - 肾上腺素能受体亚型（α₂A、α₂B和α₂C）在抑制去甲肾上腺素溢出方面发挥同等作用，而α₂C - 肾上腺素能受体是参与控制肾上腺素溢出抑制机制的主要α₂ - 肾上腺素能受体亚型。
