Fisher J T, Brundage K L, Anderson J W
Department of Physiology, Queen's University, Kingston, ON, Canada.
Can J Physiol Pharmacol. 1996 May;74(5):603-13.
We addressed the role of muscarinic receptor subtypes in neurally mediated bronchoconstriction in vivo and airway smooth muscle contraction in vitro in the newborn dog. The in vivo dose-response effects of "selective" muscarinic antagonists on changes in lung resistance (RL) and heart rate (HR) in response to electrical stimulation of the vagus nerves were obtained in four groups of newborns. Each group was exposed to a different muscarinic antagonist: M1-selective pirenzepine (pir), M2-selective AF-DX 116 (11-[2-[(diethylamino)methyl]-1-piperidinyl]acetyl-5,11-dihydro-6H-pyrid o- [2,3-b]-[1,4]-benzodiazepine-6-one), M3-selective p-F-HHSiD (p-fluoro-hexahydro-sila-difenidol), and nonselective atropine (atr). In vitro concentration-response effects of pir and AF-DX 116 were obtained for neurally induced contractions of tracheal smooth muscle, elicited by electrical field stimulation. In a separate series of experiments we measured the bronchoconstrictor response to the muscarinic agonist acetylcholine delivered by right heart injection. Muscarinic antagonists reduced RL and HR responses to vagal stimulation in a dose-dependant fashion; however, ED50 values and selectivity for airway and cardiac responses (HR/RL ED50 ratio) were significantly different between antagonists. The rank order of potencies for inhibition of the increase in RL was atr > pir, M1 > p-F-HHSiD, M3 > AF-DX 116, M2, while that for HR was atr > AF-DX 116 > pir > p-F-HHSiD. AF-DX 116 preferentially inhibited the HR response, as reflected by the lowest HR/RL ED50 ratio (p < 0.001). The remaining antagonists preferentially inhibited RL, with the highest HR/RL ED50 ratio seen for p-F-HHSiD. These data suggest that muscarinic receptor subtypes are differentiated at birth and mediate cardiac and airway responses to vagal stimulation. We did not find autoinhibitory actions of airway M2 receptors on either the in vivo bronchoconstrictor response or the in vitro contractile response to electrical field stimulation. This suggests that neonatal airway M2 receptors, but not myocardial M2 receptors, are reduced in number or weakly coupled to muscarinic signal transduction mechanisms. Direct activation of airway smooth muscle by acetylcholine caused dose-dependent increases in RL that reached a plateau at approximately 200% at 100 micrograms, similar to values reported for vagal stimulation.
我们研究了毒蕈碱受体亚型在新生犬体内神经介导的支气管收缩及体外气道平滑肌收缩中的作用。在四组新生犬中，获得了“选择性”毒蕈碱拮抗剂对迷走神经电刺激引起的肺阻力（RL）和心率（HR）变化的体内剂量-反应效应。每组分别给予不同的毒蕈碱拮抗剂：M1选择性哌仑西平（pir）、M2选择性AF-DX 116（11-[2-[(二乙氨基)甲基]-1-哌啶基]乙酰基-5,11-二氢-6H-吡啶并[2,3-b][1,4]苯并二氮杂䓬-6-酮）、M3选择性p-F-HHSiD（对氟-六氢硅二苯醚）和非选择性阿托品（atr）。对于电场刺激引起的气管平滑肌神经诱导收缩，获得了pir和AF-DX 116的体外浓度-反应效应。在另一系列实验中，我们测量了右心注射毒蕈碱激动剂乙酰胆碱后的支气管收缩反应。毒蕈碱拮抗剂以剂量依赖方式降低了对迷走神经刺激的RL和HR反应；然而，拮抗剂之间的半数有效剂量（ED50）值以及对气道和心脏反应的选择性（HR/RL ED50比值）存在显著差异。抑制RL增加的效力顺序为atr＞pir，M1＞p-F-HHSiD，M3＞AF-DX 116，M2，而对于HR的效力顺序为atr＞AF-DX 116＞pir＞p-F-HHSiD。AF-DX 116优先抑制HR反应，这通过最低的HR/RL ED50比值反映出来（p＜0.001）。其余拮抗剂优先抑制RL，p-F-HHSiD的HR/RL ED50比值最高。这些数据表明，毒蕈碱受体亚型在出生时就有差异，并介导对迷走神经刺激的心脏和气道反应。我们未发现气道M2受体对体内支气管收缩反应或对电场刺激的体外收缩反应有自抑制作用。这表明新生气道M2受体数量减少或与毒蕈碱信号转导机制的偶联较弱，而心肌M2受体并非如此。乙酰胆碱直接激活气道平滑肌导致RL剂量依赖性增加，在100微克时达到约200%的平台期，与迷走神经刺激报道的值相似。
