EC have similar pharmacokinetic properties after iv administration,
especially for relatively short t1/2 in blood and long t1/2
in brain, indicating that C and EC suffer more intense
biotransformation in blood than in brain. The fast decreasing
concentrations of unbound C and EC in blood lead to the
decrease of permeation rate across the BBB. Moreover, EC was
easily modified by the liver in blood, and the main metabolites
were glucuronide conjugates, which were considered difficult to
cross the BBB.17 Therefore, the brain distribution ratio
(AUCbrain/AUCblood) of C was calculated only to be 0.0726 ±
0.0376 while EC was 0.1065 ± 0.0531. In our previous work,
the brain distribution ratio of danshensu was calculated to be
0.25 ± 0.04. The good BBB permeability of danshensu is
probably due to its low molecular weight and low protein
binding rate of 5%.18 C and EC are stereoisomers, and a
stereoselective process was involved in the passage of these
compounds across BBB cells.30 In this study, the brain