Determination of diffusion and partition coefficients of propofol in rat brain tissue:: implications for studies of drug action in vitro
Determination of diffusion and partition coefficients of propofol in rat brain tissue:: implications for studies of drug action in vitro
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DOI：
10.1093/bja/aeh272
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发表时间：
2004-12-01
影响因子：
9.8
通讯作者：
Pearce, RA
中科院分区：
文献类型：
--
作者：
Gredell, JA;Turnquist, PA;Pearce, RA
背景丙泊酚（2，6-二异丙基苯酚）是一种广泛使用的全身麻醉剂，可调节γ-氨基丁酸A型（GABA（A））受体，这是大脑中主要的抑制性神经递质受体。先前的研究发现，影响脑切片中突触抑制所需的丙泊酚浓度远高于临床上达到的调节分离受体的游离浓度。我们测试了这是否是由于脑组织中的缓慢平衡，并确定了必须应用以达到适当脑水平的浓度。大鼠脑切片300 μ m厚，放置在100 μ M丙泊酚在人工脑脊液的时间范围从7.5到480分钟的解决方案。在这些切片中的浓度进行了测定，通过HPLC法，以确定扩散和分配系数。将5 μ M丙泊酚作用的电生理学测量速率与计算的组织浓度增加速率进行比较。扩散系数约为0.02 × 10（-6）cm（2）s（-1），脑：人工脑脊液分配系数为36。脑切片的扩散时间与丙泊酚诱导的突触反应抑制的时间过程测量结果一致，在5 h内持续增加。通过用印防己毒素（100 μ M）阻断GABA抑制来逆转这种抑制。异丙酚在灌流液中浓度为0.63 μ M时确实增强了脑切片中的抑制，这产生了与体内达到的浓度相对应的脑浓度，但平衡需要几个小时。很可能是缓慢扩散到GABA受体解释了在以前的研究中抑制诱发反应所需的高浓度（>10 μ M）。
Background. Propofol (2,6-diisopropylphenol) is a widely used general anaesthetic that modulates gamma-aminobutyric acid type A (GABA(A)) receptors, the major inhibitory neurotransmitter receptor in the brain. Previous studies have found that the concentration of propofol that is required to affect synaptic inhibition in brain slices is much higher than the free concentration that is achieved clinically and that modulates isolated receptors. We tested whether this is accounted for by slow equilibration in brain tissue, and determined the concentration that must be applied to achieve appropriate brain levels.Methods. Rat brain slices 300-mum thick were placed in a solution of 100 muM propofol in artificial cerebrospinal fluid for times ranging from 7.5 to 480 min. Concentrations in these slices were measured by HPLC to determine diffusion and partition coefficients. Electrophysiological measurements of the rate at which effects of 5 muM propofol developed were compared with the calculated rate of increase in tissue concentration.Results. The diffusion coefficient was approximately 0.02x10(-6) cm(2) s(-1), and the brain:artificial cerebrospinal fluid partition coefficient was 36. Diffusion times in brain slices agreed well with time course measurements of propofol-induced depression of synaptic responses, which continued to increase over 5 h. This depression was reversed by blocking GABA inhibition with picrotoxin (100 muM).Conclusions. Propofol does enhance inhibition in brain slices at a concentration of 0.63 muM in the superfusate, which produces brain concentrations corresponding with those achieved in vivo, but equilibration requires several hours. It is likely that slow diffusion to GABA receptors accounts for the high concentrations (>10 muM) that were needed to depress evoked responses in previous investigations.