Modification of diazepam's antileptazol activity by endogenous tryptophan-like compounds

Three possible endogenous ligands for benzodiazepine receptors, beta-carboline-3-carboxylic acid ethyl ester (beta CCE), tryptophylglycine (Trp-Gly) and ACTH peptides, have been tested, following intracerebroventricular (i.c.v.) administration in mice, for their direct effects on the CNS and the modification of diazepam's antileptazol activity. Whilst beta CCE and ACTH both reduced diazepam's antileptazol activity, only beta CCE had direct stimulant effects. Trp-Gly produced sedation and augmented the antileptazol effect of diazepam. Despite these differing effects, it remains possible that the endogenous ligand for the benzodiazepine receptors has a tryptophan-like structure.