Kerry R, Scrutton M C
Br J Pharmacol. 1983 Jul;79(3):681-91. doi: 10.1111/j.1476-5381.1983.tb10005.x.
Inhibition by isoprenaline of the aggregatory response of human and rat platelets induced by various excitatory agonists is blocked by beta 2-adrenoceptor antagonists. beta 1-Adrenoceptor antagonists are ineffective. beta 2-Adrenoceptor agonists cause inhibition of the response of human platelets to various excitatory agonists. The maximal extent of inhibition is less than that observed for isoprenaline. beta 1-Adrenoceptor agonists fail to cause detectable inhibition of this response. Neither beta 1 nor beta 2-adrenoceptor agonists cause inhibition of the response of rat platelets to excitatory agonists. Only beta 2-adrenoceptor agonists block the inhibitory response to isoprenaline. The extent of inhibition by isoprenaline is a function of the excitatory agonist used and in human platelets is correlated with the ability of that agonist to suppress elevated platelet cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels. Inhibition by isoprenaline is prevented in the presence of an inhibitor of adenylate cyclase. Isoprenaline increases platelet cyclic AMP levels with an EC50 similar to that required to observe inhibition of the aggregatory response. These data indicate that human platelets carry beta 2-adrenoceptors whose occupancy causes inhibition of the response to excitatory agonists as a consequence of elevation of platelet cyclic AMP. The beta-adrenoceptor present on rat platelets also appears to be of the beta 2-subtype.
异丙肾上腺素对多种兴奋性激动剂诱导的人及大鼠血小板聚集反应的抑制作用可被β2 -肾上腺素能受体拮抗剂阻断。β1 -肾上腺素能受体拮抗剂则无效。β2 -肾上腺素能受体激动剂可抑制人血小板对多种兴奋性激动剂的反应。最大抑制程度小于异丙肾上腺素所观察到的。β1 -肾上腺素能受体激动剂未能引起该反应的可检测到的抑制作用。β1和β2 -肾上腺素能受体激动剂均未引起大鼠血小板对兴奋性激动剂反应的抑制。只有β2 -肾上腺素能受体激动剂可阻断对异丙肾上腺素的抑制反应。异丙肾上腺素的抑制程度是所用兴奋性激动剂的函数，在人血小板中与该激动剂抑制升高的血小板环磷酸腺苷（环磷腺苷）水平的能力相关。在腺苷酸环化酶抑制剂存在的情况下，异丙肾上腺素的抑制作用被阻止。异丙肾上腺素使血小板环磷腺苷水平升高，其半数有效浓度（EC50）与观察到聚集反应抑制所需的浓度相似。这些数据表明，人血小板带有β2 -肾上腺素能受体，其占据导致由于血小板环磷腺苷升高而抑制对兴奋性激动剂的反应。大鼠血小板上存在的β -肾上腺素能受体似乎也是β2 -亚型。
