Fig. 3. Partition and diffusion coefficients for etomidate in brain tissue. Brain slices (400 μm) were incubated in artificial cerebrospinal fluid containing 3.27 μm etomidate for durations ranging from 0.67 to 360 min. The total amount in each slice was measured by extraction and high-performance liquid chromatography analysis. Each data point represents the average of duplicate measurements within the same slice. ( A ) The data were fitted by a monoexponential function with a time constant of 9.5 min. The steady state concentration of etomidate, 2,682 ± 155 ng/g brain, yielded a partition coefficient of 3.35 ± 0.18. ( B ) Uptake data obtained during the first 60 min of incubation conformed most closely to a diffusion coefficient of D = 0.2 × 10−6cm2/s.