Hesselink M B, Parsons C G, Wollenburg C, Danysz W
Department of Pharmacological Research, Merz + Co., Frankfurt/Main, Germany.
Naunyn Schmiedebergs Arch Pharmacol. 1999 Aug;360(2):144-50. doi: 10.1007/s002109900056.
Although the concentration of drugs in brain homogenates is relatively easy to determine, such data are sometimes misleading due to accumulation in intracellular compartments. This is apparent for uncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists where concentrations assessed in this manner are much higher than those sufficient to block the NMDA channel from the extracellular space. The aim of the present study was to determine whether free brain concentrations (extracellular fluid - ECF) of a new uncompetitive NMDA receptor antagonist MRZ 2/579 (1-amino-1,3,3,5,5-pentamethyl-cyclohexane hydrochloride) following administration of doses effective in animal models are sufficient to block NMDA receptors based on its potency in vitro. This issue was addressed using brain microdialysis corrected for in vivo recovery and patch clamp experiments.MRZ 2/579 blocked steady-state inward current responses of cultured hippocampal neurones to NMDA with an IC50 of 1.11 microM at -70 mV. Much higher concentrations of MRZ 2/579 blocked voltage-activated Ca2+ channels with an IC50 of 340 microM. MRZ 2/579 (10 microM) reduced peak inward current responses of neuronal nicotinic receptors only to 72.3% of control. MRZ 2/579 (10-100 microM) had little or no effect at AMPA and GABA(A) receptors. Following chronic s.c. infusion of MRZ 2/579 (40 mg/kg day for 7 days) brain ECF (2.15 microM) and cerebro-spinal fluid (CSF) levels (2.16 microM) were twofold lower than free plasma levels (4.3 microM). MRZ 2/579 showed pronounced accumulation in brain tissue compared to free plasma (28-fold) and ECF (58-fold). After acute i.p. administration (5, 10 and 20 mg/kg) peak concentrations in ECF were 0.70, 0.96 and 2.53 microM, respectively. In conclusion, MRZ 2/579 is indeed strongly accumulated in brain tissue compared to brain ECF, CSF and plasma. However, the brain ECF levels attained following administration of behaviourally effective doses are sufficient for selective NMDA receptor blockade.
虽然脑匀浆中药物浓度相对容易测定，但由于药物在细胞内区室的蓄积，此类数据有时会产生误导。对于非竞争性N-甲基-D-天冬氨酸（NMDA）受体拮抗剂而言，情况尤为明显，用这种方式评估的浓度远高于足以从细胞外空间阻断NMDA通道的浓度。本研究的目的是确定一种新型非竞争性NMDA受体拮抗剂MRZ 2/579（1-氨基-1,3,3,5,5-五甲基环己烷盐酸盐）在给予对动物模型有效的剂量后，其脑内游离浓度（细胞外液-ECF）根据其体外效力是否足以阻断NMDA受体。使用经体内回收率校正的脑微透析和膜片钳实验解决了这个问题。MRZ 2/579在-70 mV时以1.11 microM的IC50阻断培养的海马神经元对NMDA的稳态内向电流反应。更高浓度的MRZ 2/579以340 microM的IC50阻断电压激活的Ca2+通道。MRZ 2/579（10 microM）仅将神经元烟碱受体的内向电流峰值反应降低至对照的72.3%。MRZ 2/579（10 - 100 microM）对AMPA和GABAA受体几乎没有影响。在慢性皮下输注MRZ 2/579（40 mg/kg/天，共7天）后，脑ECF（2.15 microM）和脑脊液（CSF）水平（2.16 microM）比游离血浆水平（4.3 microM）低两倍。与游离血浆（28倍）和ECF（58倍）相比，MRZ 2/579在脑组织中显示出明显的蓄积。急性腹腔注射（5、10和20 mg/kg）后，ECF中的峰值浓度分别为0.70、0.96和2.53 microM。总之，与脑ECF、CSF和血浆相比，MRZ 2/579确实在脑组织中大量蓄积。然而，给予行为有效剂量后达到的脑ECF水平足以实现选择性NMDA受体阻断。
