beta-Carboline inhibition of benzodiazepine receptor binding in vivo

The in vivo potencies of 4 beta-carboline derivatives as inhibitors of benzodiazepine receptor binding were investigated. For all 4 derivatives maximal inhibition was seen within 2 min after i.v. application but decreased continuously for the next 20 min and after this time accounted for less than one-third of maximal inhibition. The in vivo potencies of the beta-carbolines as inhibitors of benzodiazepine receptor binding are much smaller than one would expect from their affinities measured in vitro. Thus, it is assumed than only a small portion of the i.v. dose reaches the brain.