Weiss R J, Webb R C, Smith C B
J Hypertens. 1984 Jun;2(3):249-55.
Alpha 2 adrenoreceptors are located on vascular smooth muscle of the rat tail artery. In the present study this receptor was studied in spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Adrenergic agonists were used to produce isometric contractions of helically-cut tail artery strips from SHR and WKY. Clonidine and guanabenz, alpha 2 agonists, were more potent in the SHR than in the WKY (e.g. clonidine: EC50 SHR = 3.5 +/- 0.6 X 10(-8) M; EC50 WKY = 17.0 +/- 0.2 X 10(-8) M; P less than 0.0005). There was no difference in potency between the alpha 1 agonists, phenylephrine and methoxamine. Yohimbine, an alpha 2 antagonist, was more potent in inhibiting the clonidine-induced contraction in the SHR (pA2 = 7.66 versus 7.14). To determine the number of alpha 2 adrenoreceptors, the specific binding of 3H-clonidine to homogenates of tail artery and of five brain areas was also measured. The maximum number of high-affinity sites on the tail artery was threefold greater in SHR than in WKY (31 +/- 5 versus 11 +/- 3 fmol/mg protein, P less than 0.0005). No differences in the number or affinity of alpha 2 receptor sites was found in the hypothalamus, hippocampus, locus coeruleus or parietal cortex of the two strains of rat. There was a difference in the amygdala (SHR: 163 +/- 16 versus WKY: 108 +/- 14, P less than 0.05). The larger number of alpha 2 adrenoreceptors on the vascular smooth muscle in SHR may provide an explanation for the supersensitivity of SHR to adrenergic agonists.
α2肾上腺素能受体位于大鼠尾动脉的血管平滑肌上。在本研究中，对自发性高血压大鼠（SHR）和Wistar-Kyoto大鼠（WKY）的这种受体进行了研究。使用肾上腺素能激动剂使SHR和WKY的螺旋形尾动脉条产生等长收缩。α2激动剂可乐定和胍那苄在SHR中比在WKY中更有效（例如可乐定：SHR的EC50 = 3.5±0.6×10（-8）M；WKY的EC50 = 17.0±0.2×10（-8）M；P＜0.0005）。α1激动剂去氧肾上腺素和甲氧明的效力没有差异。α2拮抗剂育亨宾在抑制SHR中可乐定诱导的收缩方面更有效（pA2 = 7.66对7.14）。为了确定α2肾上腺素能受体的数量，还测量了3H-可乐定与尾动脉和五个脑区匀浆的特异性结合。SHR尾动脉上高亲和力位点的最大数量比WKY大三倍（31±5对11±3 fmol/mg蛋白质，P＜0.0005）。在两种品系大鼠的下丘脑、海马、蓝斑或顶叶皮质中，未发现α2受体位点的数量或亲和力有差异。杏仁核存在差异（SHR：163±16对WKY：108±14，P＜0.05）。SHR血管平滑肌上较多的α2肾上腺素能受体可能为SHR对肾上腺素能激动剂的超敏反应提供了解释。
