Simple and sensitive methods are developed for microdetermination of drugs acting on the central nervous system. The assay employs the partially purified synaptosomal membrane isolated from rat brain. In the assay, 3H-Quinuclidinyl benzylate competes with drugs for binding to the receptor. The detection limit for scopolamine was 20 ng/ml. This method was applied for the measurement of other drugs acting on the central nervous system. The values of IC50 were lower than 0.1μg/ml in biperiden, trihexyphenidyl, levomepromazine, and promethazine.
The method has been used to determine plasma levels in 9-week-old and 21-week-old rats after i. v. injection of 1 mg/kg scopolamine. The blood levels of scopolamine at each time after the administration are significantly different between 9-week-old and 21-week-old rats. The values of Vdss determined in 21-week-old rats were significantly increased as compared to the 9-week-old rats, whereas CLtot were not changed.
