Arribas S, Galvan R, Ferrer M, Herguido M J, Marin J, Balfagón G
Departamento de Fisiología, Facultad de Medicina, Universidad Autónma Madrid, Spain.
J Pharm Pharmacol. 1991 Dec;43(12):855-9. doi: 10.1111/j.2042-7158.1991.tb03194.x.
The possible existence of a heterogeneous population of alpha 2-adrenoceptors (alpha 2A and alpha 2B, demonstrated by binding studies) in adrenergic nerve endings of cat and bovine cerebral arteries modulating noradrenaline release was investigated. Electrical field stimulation elicited an increase of tritium secretion from these vessels preincubated with (+/-)-[3H]noradrenaline, which was reduced by the alpha 2-agonists, clonidine (1 microM) and B-HT 920 (0.01 and 0.1 microM), in cat cerebral arteries but only by B-HT 920 in bovine cerebral arteries. This reduction was inhibited by the antagonist of the alpha 2B-subtype, prazosin, and the antagonists of alpha 2A- and alpha 2B-subtypes yohimbine and particularly rauwolscine. The effect of B-HT 920 was partially inhibited by clonidine in bovine, but not in cat cerebral arteries. In both types of arteries, prazosin, yohimbine and the alpha 1-agonist methoxamine (all at 1 microM) failed to modify the stimulated radioactivity liberation, whereas it was increased by 1 microM rauwolscine, and by yohimbine plus prazosin in cat cerebral arteries. The basal tritium release was enhanced by rauwolscine and prazosin in cat cerebral arteries but only by the latter in bovine cerebral arteries. These results suggest: (1) the existence of presynaptic alpha 2-adrenoceptors, mainly of the alpha 2B-subtype, in these vessels negatively modulating noradrenaline release, their activity being greater in cat than in bovine cerebral arteries, and (2) clonidine has no agonistic but a weak antagonistic action in the latter vessels.
研究了猫和牛脑动脉肾上腺素能神经末梢中可能存在的异质性α2-肾上腺素能受体群体（结合研究证明为α2A和α2B）对去甲肾上腺素释放的调节作用。电场刺激使预先用（±）-[3H]去甲肾上腺素孵育的这些血管中的氚分泌增加，在猫脑动脉中，α2-激动剂可乐定（1μM）和B-HT 920（0.01和0.1μM）可使其减少，但在牛脑动脉中仅B-HT 920可使其减少。这种减少被α2B亚型拮抗剂哌唑嗪以及α2A和α2B亚型拮抗剂育亨宾尤其是利血平抑制。在牛脑动脉中，可乐定可部分抑制B-HT 920的作用，但在猫脑动脉中则不然。在两种类型的动脉中，哌唑嗪、育亨宾和α1-激动剂甲氧明（均为1μM）均未能改变刺激后的放射性释放，而在猫脑动脉中，1μM利血平以及育亨宾加哌唑嗪可使其增加。在猫脑动脉中，利血平和哌唑嗪可增强基础氚释放，但在牛脑动脉中仅哌唑嗪有此作用。这些结果表明：（1）这些血管中存在突触前α2-肾上腺素能受体，主要为α2B亚型，对去甲肾上腺素释放起负调节作用，其活性在猫脑动脉中比在牛脑动脉中更强；（2）可乐定在后者血管中无激动作用，但有微弱的拮抗作用。
