STUDY ON THE ENANTIO-SELECTIVITY OF S(+)-KETAMINE ON THE REGULATION OF CIRCULATION

本研究旨在探讨外消旋氯胺酮和S(+)-氯胺酮在全身麻醉下硬膜外注射对循环的影响机制。全动物实验采用1% （0.5MAC）异氟醚麻醉家兔。低胸硬膜外给予外消旋氯胺酮和S(+)-氯胺酮0.5 mg/kg和1.0 mg/kg，均可显著降低动脉压、肾交感神经活动。然而，既没有剂量依赖性，也没有对映体选择性。毒蕈碱M2受体和一氧化氮可能与这种血流动力学变化无关。抑制心肌收缩需要高浓度的消旋氯胺酮或S(+)-氯胺酮（IC50约为300 μ m）。这种作用源于这些药物的钠通道阻断作用。同样，神经周围高浓度的氯胺酮可能阻断了交感神经的传播，因此没有发现两种药物之间的差异。从脊髓中外侧细胞柱分离和培养细胞是困难的。我们利用大鼠小胶质细胞系对这些细胞进行膜片钳研究。临床相关浓度的硫喷妥钠可增强P2X7受体电流，而临床相关浓度的氯胺酮（100 M）对P2X7受体电流无显著影响。使用对ATP具有高灵敏度和选择性的生物传感器，在脊髓中实时测量ATP作为细胞外递质。缺氧等刺激引起神经损伤。测定脊髓ATP浓度和交感神经活动，研究S(+)-氯胺酮和外消旋氯胺酮的作用。然而，在各种条件下均未观察到ATP浓度的增加。重新评估ATP生物传感器的可靠性是必要的。

The purpose of this study was to elucidate the mechanism on circulatory effects of epidural administration of racemic ketamine and S(+)-ketamine during concomitant use of general anesthesia. For whole animal study, rabbits anesthetized with 1 % (0.5MAC) isoflurane were used. Low thoracic epidural administration of racemic ketamine and S(+)-ketamine, 0.5 mg/kg and 1.0 mg/kg, both significantly reduced arterial pressure, renal sympathetic nerve activity. However, neither dose-dependency nor enantio-selectivity was demonstrated. Muscarinic M2 receptors and nitric oxide may not be involved in this hemodynamic change. High concentration of racemic ketamine or S(+)-ketamine (IC50 was approximately 300 uM) was required to suppress myocardial contractility. This effect is originated from the sodium channel blocking effects of these drugs. Similarly, high concentrations of ketamine at the perineurium may have blocked sympathetic nerve propagation thus no difference between the two drugs was detected.Separation and culture of the cells from the intermediolateral cell columns in the spinal cord was difficult. Instead, rat microglial cell line was available so we did patch clamp study on these cells. Clinically relevant concentrations of thiopental enhanced P2X7 receptor currents, but clinically relevant concentrations of ketamine (100 M) did not significantly change P2X7 receptor currents. Real-time measurement of ATP as an extracellular transmitter was performed in the spinal cord using a biosensor which has high sensitivity and selectivity to ATP. Neural damage was induced by hypoxic challenge etc. ATP concentrations in the spinal cord and sympathetic nerve activity were measured and effects of S(+)-ketamine and racemic ketamine were studied. However, inclease in ATP concentrations was never observed with various conditions. Reevaluation of the reliability of the ATP biosensor was necessary.