Effects of inhalation anesthetics on parasympathetic reflex vasodilatation

本实验旨在研究吸入麻醉剂（异氟烷，氟烷，七氟烷）的影响，在下唇和腭引起的舌神经的中央切断端的电刺激迷走神经交感神经切除猫的副交感神经反射血管舒张。异氟醚（1.5%）、氟烷（1.0%）、七氟醚（2.5%）（最低肺泡浓度1.0MAC）均能明显抑制诱发的下唇血流量增加，而氧化亚氮（70%）和吗啡（2 mg/kg，iv）则无此作用。预先静脉注射GABA拮抗剂印防己毒素（2 mg/kg）可逆转异氟醚对副交感神经反射的抑制作用。去大脑对异氟烷诱导的抑制作用无显著影响。这些发现表明，有GABA介导的抑制机制作用于这种副交感神经反射反应;吸入麻醉剂发挥这种抑制作用的部位可能在中脑、脑桥或髓质，但不在下丘脑或更高结构。

The present experiments were designed to examine the effects of inhalation anesthetics (isoflurane, halothane, and sevoflurane) on the parasympathetic reflex vasodilation in the lower lip and palate elicited by electrical stimulation of the central cut end of the lingual nerve in vago-sympathectomized cats. Isoflurane (1.5%), halothane (1.0 %), sevoflurane (2.5%), each at a concentration of 1.0 MAC (minimum alveolar concentra-tion), markedly suppressed the evoked blood flow increases in the lower lip, whereas nitrous oxide (70 % in 30% oxygen) and morphine (2 mg/kg, iv) did not. Prior administra-tion of picrotoxin, a GABA antagonist, (2 mg/kg, iv) reversed the inhibitory effect of isoflurane on the parasympathetic reflex response. Decerebration had no significant effect on the isoflurane-induced inhibition. These findings suggest that there is a GABA-mediated suppressive mechanism acting on this parasympathetic reflex response ; the sites at which inhalation anesthetics exert such an inhibitory action could be in the mid-brain, pons, or medulla, but not in the hypothalamus or higher structures.