Implementation of a Radioreceptor Assay for Dexmedetomidine

: We have implemented a radioreceptor assay for dexmedetomidine, a novel α2‐adrenoceptor agonist. Receptor‐bearing membranes were prepared from rat cerebral cortex and 3H‐clonidine, 4 nM, was used as the labeled ligand. Dexmedetomidine displaced 3H‐clonidine in a linear fashion over a concentration of 2 × 10‐10 to 2 × 10‐8 M. The detection limit of dexmedetomidine (i.e. 10% of radiolabeled ligand displaced) in this assay was 50 pg.ml‐1 which is comparable to that seen with the reference method which utilizes gas chromotography with mass spectrometer (GC/MS) in series (Vuorilehto et al. 1989). Endogenous catecholamines, which can displace the radiolabeled ligand from its binding site, could easily be eliminated with a one‐step extraction procedure. A comparison was made with the reference method (GC/MS) in 47 human plasma samples; the correlation coefficient (r2) was 0.61 (P