[The tissue distribution of racemic S-(+)- and R-(R)-(-)-MPPB (1-methyl-5-phenyl-5-propylbarbituric acid) in the rat].

Distribution of racemic 1-methyl-5-phenyl-5-propyl-barbituric acid (= racem. MPPB), of the S-(+)- and R-(-)-enantiomer (= (+)- and (-)-MPPB) between serum and several tissues was investigated after i.v. administration of the substances to rats. Anesthesia produced by the racem. MPPB--(+)-MPPB causes convulsions whereas (-)-MPPB is anesthetically active--cannot be explained by a stereoselective difference of the MPPB-concentration measured in serum and brain when giving the enantiomers. Reversely as expected in the brain MPPB-concentration is significantly higher after administration of (+)-MPPB than after that of (-)-MPPB during the appearance of the CNS symptoms.--Significant stereoselectively different MPPB-concentrations, which are time dependent, could also be detected in liver, spleen and fatty tissue; however, in contrast to the brain in these tissues MPPB-concentration is higher after administration of (-)-MPPB than after that of (+)-MPPB. Concentration differences which are measured in liver, spleen and fatty tissue already 1--10 min after i.v. administration of the enantiomers cannot be explained by a stereoselectivity of the metabolism and/or renal elimination. However, a stereoselective metabolism and/or renal elimination of the enantiomers can be responsible for concentration differences which are observed during the late period of 60--180 min after administration: in serum, brain, liver and fatty tissue MPPB-concentration is lower if (4)-MPPB is administered. For that reason it can be supposed that (+)-MPPB is faster eliminated than (-)-MPPB.