Wallick D W, Stuesse S L, Martin P
Division of Investigative Medicine, Mount Sinai Medical Center, Cleveland, OH 44106.
Can J Physiol Pharmacol. 1990 Oct;68(10):1363-7. doi: 10.1139/y90-206.
A brief electrical stimulation of the vagus nerve may elicit a triphasic response comprising (i) an initial prolongation of the same or the next cardiac cycle, (ii) a return of the subsequent cardiac cycle to about the level prior to vagal stimulation, and (iii) a secondary prolongation of cardiac cycle length that lasts several beats. We compared the effects of two calcium channel antagonists, verapamil and nifedipine, on this triphasic response to vagal stimulation in chloralose-anesthetized, open-chest dogs. In the absence of vagal stimulation, nifedipine (doses of 10, 40, and 50 micrograms/kg for a total dose of 100 micrograms/kg, i.v.) and verapamil (two doses of 100 micrograms/kg each, i.v.) increased the cardiac cycle length (A-A interval) by 16% (429 +/- 20 to 496 +/- 21 ms) and 29% (470 +/- 33 to 605 +/- 54 ms), respectively. Nifedipine (100 micrograms/kg total) attenuated the initial vagally mediated prolongation of the A-A interval, from 474 +/- 19 to 369 +/- 42 ms above the basal A-A interval. Following the initial prolongation of the vagal effect, other A-A intervals were not affected. In contrast, verapamil potentiated the vagally mediated initial prolongation in cardiac cycle length at the first dose administered (100 micrograms/kg) from 492 +/- 17 to 561 +/- 14 ms, but other increases in dosages had no further effect. Thus these two calcium channel antagonists have different effects on the sinoatrial chronotropic responses caused by brief vagal stimulation.
对迷走神经进行短暂电刺激可能会引发一种三相反应，包括：（i）同一心动周期或下一个心动周期最初的延长；（ii）随后的心动周期恢复到迷走神经刺激前的大致水平；（iii）心动周期长度的继发性延长，持续几个搏动。我们比较了两种钙通道拮抗剂维拉帕米和硝苯地平对氯醛糖麻醉、开胸犬迷走神经刺激所致三相反应的影响。在无迷走神经刺激时，硝苯地平（静脉注射剂量分别为10、40和50微克/千克，总剂量100微克/千克）和维拉帕米（静脉注射，每次剂量100微克/千克）分别使心动周期长度（A - A间期）增加16%（从429±20毫秒增至496±21毫秒）和29%（从470±33毫秒增至605±54毫秒）。硝苯地平（总剂量100微克/千克）减弱了迷走神经介导的A - A间期最初的延长，从高于基础A - A间期474±19毫秒减至369±42毫秒。迷走神经效应最初延长后，其他A - A间期未受影响。相比之下，维拉帕米在首次给药剂量（100微克/千克）时增强了迷走神经介导的心动周期长度最初的延长，从492±17毫秒增至561±14毫秒，但其他剂量增加未产生进一步影响。因此，这两种钙通道拮抗剂对短暂迷走神经刺激引起的窦房结变时性反应具有不同影响。
