McRitchie R J, Chalmers J P
J Cardiovasc Pharmacol. 1981 Jul-Aug;3(4):818-27. doi: 10.1097/00005344-198107000-00015.
Both clonidine and labetalol when given by bolus intravenous injection into conscious rabbits produce an initial rise in left ventricular pressure associated with a decrease in myocardial contractility as assessed by left ventricular dP/dt. While clonidine also produces a marked bradycardiac effect, labetalol causes no change in heart rate. Acute beta-adrenoceptor blockade with propranolol, 1 mg/kg, i.v., does not significantly modify the response produced by either clonidine or labetalol. Following cardiac cholinergic blockade with scopolamine methylbromide, 50 microgram/kg, the negative inotropic effect produced by clonidine is abolished and is replaced by a positive inotropic effect, while the negative inotropic response produced by labetalol is attenuated. Following cardiac autonomic blockade with propranolol and scopolamine methyl-bromide, both clonidine and labetalol produce a positive inotropic response. These positive inotropic responses may be due to the partial alpha-adrenoceptor-agonist properties which both drugs possess and which could be unmasked by cardiac autonomic blockade.
给清醒家兔静脉推注可乐定和拉贝洛尔，两者均会使左心室压力出现初始升高，同时左心室dP/dt评估显示心肌收缩力下降。可乐定还会产生显著的心动过缓效应，而拉贝洛尔对心率无影响。静脉注射1mg/kg普萘洛尔进行急性β肾上腺素能受体阻断，并不会显著改变可乐定或拉贝洛尔产生的反应。用50μg/kg甲基溴化东莨菪碱进行心脏胆碱能阻断后，可乐定产生的负性肌力作用消失，取而代之的是正性肌力作用，而拉贝洛尔产生的负性肌力反应减弱。在用普萘洛尔和甲基溴化东莨菪碱进行心脏自主神经阻断后，可乐定和拉贝洛尔均产生正性肌力反应。这些正性肌力反应可能归因于两种药物都具有的部分α肾上腺素能受体激动剂特性，且这种特性可被心脏自主神经阻断所揭示。
