Abstract
The two enantiomers ((R)- and (S)-) of propranolol glycol, a metabolite of propranolol, have been synthesized, and their effects upon the β-adrenoceptor studied by two methods. The ability of these compounds to antagonize the inotropic actions of isoprenaline was examined on spontaneously beating rat atrial preparations. Also, the effects of these enantiomers upon the binding of [3H]dihydroalprenolol to β-receptors in rat cardiac ventricular membranes was studied. Experiments with the atria indicated that the (S)-glycol was a reversible competitive antagonist of isoprenaline with a potency approximately one thousand times lower than that of (±)-propranolol. In contrast, the (R)-glycol appeared to act as an irreversible antagonist, producing complex dose-response curves. The effects of these compounds to cause displacement of alprenolol binding were consistent with the organ bath data. The interaction of the (S)-glycol with the β-receptor binding site was reversible (Ki of 27ṁ6 ± 4ṁ2 μM) but less potent than that of (±)-propranolol (Ki of 0ṁ99 ± 0ṁ07 nM). On the other hand, pretreatment of ventricular membranes with the (R)-glycol, followed by extensive washing techniques, resulted in alprenolol binding which did not regain control values, providing further evidence for an irreversible effect upon the β-receptor. The possible significance of these pharmacological actions of the two enantiomers is discussed in terms of the in-vivo metabolic pathways for propranolol.
摘要:合成了普萘洛尔的代谢产物普萘洛尔甘醇的两个对映体((R)-和(S)-),并通过两种方法研究了它们对β-肾上腺素受体的影响。这些化合物拮抗异丙肾上腺素的正性肌力作用的能力在自发跳动的大鼠心房制备物上进行了检查。此外,研究了这些对映体对[3H]双氢异丙肾上腺醇与大鼠心脏室壁膜上β受体的结合的影响。心房实验表明,(S)-甘醇是异丙肾上腺素的可逆竞争性拮抗剂,其效力约为(±)-普萘洛尔的一千分之一。相反,(R)-甘醇似乎作为一种不可逆拮抗剂,产生复杂的剂量-反应曲线。这些化合物引起阿普诺洛尔结合位点的位移效应与器官浴数据一致。与β受体结合位点的(S)-甘醇的相互作用是可逆的(Ki为27.6 ± 4.2 μM),但比(±)-普萘洛尔(Ki为0.99 ± 0.07 nM)的效力低。另一方面,用(R)-甘醇预处理心室膜,随后进行广泛的洗涤技术处理,导致阿普诺洛尔结合未恢复到对照值,进一步证明对β受体具有不可逆效应。讨论了这两个对映体的药理作用在普萘洛尔的体内代谢途径方面的可能意义。