Biochemical studies with the new thienotriazolo-diazepine brotizolam

Brotizolam (2-bromo-4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f]-1,2,4-triazolo [4,3-a]-1,4-diazepine, We 941, Lendormin) is a newly developed thienotriazolo-diazepine with distinct hypnotic effects. It was biochemically characterized by performing various receptor binding studies, uptake and release studies in vitro and determining homovanillic acid brain concentrations in vivo. Using [3H]-flunitrazepam as a radioligand, brotizolam showed an extremely high affinity for specific benzodiazepine binding sites in the rat brain, demonstrated by an IC50 value of 1.0 nmol/l. Using both [3H]-flunitrazepam and [3H]-brotizolam as radioligands, a strong correlation between the IC50 values of brotizolam and various benzodiazepines could be shown. [3H]-Flunitrazepam as well as [3H]-brotizolam bound with similar affinities to cerebellar and hippocampal synaptosomal membranes. In contrast to [3H]-flunitrazepam binding, however, [3H]-brotizolam had twice the number of specific binding sites in the hippocampus. According to the maximum binding of [3H]-flunitrazepam, the inhibition curve of brotizolam also increased in the presence of 10(-4) mol/l gamma-aminobutyric acid and decreased remarkably in the presence of 10(-4) mol/l bicuculline. Using [3H]-muscimol as a ligand, a modulating effect of brotizolam could be shown by increasing the low affinity with no change in the number of binding sites. From various further receptor binding studies, as well as from in vitro uptake and release studies of [3H]-noradrenaline, [3H]-serotonin and [3H]-dopamine, no indication was found of another biochemical effect of brotizolam. There was also no change in the homovanillic acid concentration in the rat brain striata in vivo after brotizolam treatment.(ABSTRACT TRUNCATED AT 250 WORDS)