Kenakin T P, Beek D
J Auton Pharmacol. 1984 Sep;4(3):153-9. doi: 10.1111/j.1474-8673.1984.tb00092.x.
Isoprenaline, but not prenalterol, produced positive inotropy in guinea-pig papillary muscle. Prenalterol was a competitive antagonist of responses to isoprenaline in this tissue with a pKB of 7.24, as estimated by a Schild regression. Guinea-pig papillary muscles pretreated with the phosphodiesterase inhibitor, isobutylmethylxanthine (IMX), were 10 times more sensitive than controls to isoprenaline. In these tissues, prenalterol was a partial agonist producing 68% of the maximal response to isoprenaline. Schild regressions with atenolol indicated no change in beta-adrenoreceptors with IMX treatment and also that isoprenaline and prenalterol activated the same receptor in this tissue. The relative efficacy of isoprenaline and prenalterol was measured by using the KB estimated by Schild analysis for prenalterol and a Kd for isoprenaline from published binding studies. The relative efficacy of these drugs (epsilon ISO/epsilon PREN) was 242 +/- 29. The general method of potentiation of responses to weak agonists to estimate relative efficacy is discussed.
异丙肾上腺素能使豚鼠乳头肌产生正性肌力作用，而普瑞特罗则不能。通过Schild回归分析估计，普瑞特罗是该组织中对异丙肾上腺素反应的竞争性拮抗剂，其pKB为7.24。用磷酸二酯酶抑制剂异丁基甲基黄嘌呤（IMX）预处理的豚鼠乳头肌对异丙肾上腺素的敏感性比对照高10倍。在这些组织中，普瑞特罗是一种部分激动剂，产生的最大反应为异丙肾上腺素的68%。用阿替洛尔进行的Schild回归分析表明，IMX处理后β-肾上腺素受体无变化，且异丙肾上腺素和普瑞特罗在该组织中激活相同的受体。通过使用Schild分析估计的普瑞特罗的KB和已发表的结合研究中异丙肾上腺素的Kd来测量异丙肾上腺素和普瑞特罗的相对效能。这些药物的相对效能（εISO/εPREN）为242±29。讨论了增强对弱激动剂反应以估计相对效能的一般方法。
