THROMBOXANE A2 AS A POSSIBLE NATURAL LIGAND FOR BENZODIAZEPINE RECEPTORS

Receptors for benzodiazepines were recently found in the brain but the natural ligand which can occupy these receptors is unknown. In a rat vascular preparation diazepam and chlordiazepoxide inhibited pressor responses to noradrenaline [norepinephrine] and angiotensin but not those to K and vasopressin with IC50 [median inhibitory concentration] concentrations similar to those reported for displacement of [3H]diazepam from brain receptors. Imidazole, an inhibitor of thromboxane A2 synthesis, had similar actions to the benzodiazepines. Interactions between imidazole and the benzodiazepines suggested that the latter may be competitive antagonists of thromboxane A2. The possibility that thromboxane A2 may be the natural ligand is supported by recent evidence that brain tissue contains high levels of this substance.