McWilliam P N, Woolley D C
Department of Cardiovascular Studies, University of Leeds, U.K.
J Auton Nerv Syst. 1988 Feb;22(1):67-73. doi: 10.1016/0165-1838(88)90155-5.
The bradycardia and reduction in atrial contraction on electrical stimulation of the peripheral cut end of the vagus nerve in the cat have been attributed solely to the action of myelinated fibres. In the rabbit however, recruitment of non-myelinated fibres produces an additional prolonged bradycardia. The objective of this investigation was to examine the relative contributions of myelinated and non-myelinated fibres to the vagal action on atrial contraction in the rabbit. In 5 rabbits stimulation of myelinated fibres at 10 Hz for 20 s reduced developed atrial tension of the paced heart by 17.1 +/- 2.6%. After stimulation, atrial tension returned rapidly to the control value in 6.5 +/- 0.5 s. Recruitment of non-myelinated fibres resulted in a reduction in developed atrial tension of 29.1 +/- 2.8%. This larger fall in atrial tension outlasted the period of stimulation by 34.1 +/- 4.8 s. Hexamethonium blocked the reduction in atrial contraction due to myelinated fibres but not that due to non-myelinated fibres. Atropine abolished all effects of vagal stimulation on atrial contraction. We conclude that the recruitment of non-myelinated fibres produces an additional prolonged reduction in atrial contraction which is resistant to hexamethonium but blocked by atropine.
猫迷走神经外周切断端受到电刺激时出现的心动过缓和心房收缩减弱，一直被认为完全是由有髓纤维的作用所致。然而，在兔身上，募集无髓纤维会产生额外的持续性心动过缓。本研究的目的是探讨有髓纤维和无髓纤维对兔迷走神经作用于心房收缩的相对贡献。在5只兔中，以10Hz刺激有髓纤维20秒，使起搏心脏的心房张力峰值降低了17.1±2.6%。刺激后，心房张力在6.5±0.5秒内迅速恢复到对照值。募集无髓纤维导致心房张力峰值降低29.1±2.8%。这种心房张力的更大幅度下降在刺激期后持续了34.1±4.8秒。六甲铵可阻断有髓纤维引起的心房收缩减弱，但不能阻断无髓纤维引起的心房收缩减弱。阿托品可消除迷走神经刺激对心房收缩的所有影响。我们得出结论，募集无髓纤维会使心房收缩出现额外的持续性减弱，这种减弱对六甲铵有抗性，但可被阿托品阻断。
