Radioreceptor assay for the determination of alpha 1-adrenoceptor-binding material in rat plasma following single oral administration of naftopidil.

Naftopidil could be characterized by receptor binding studies as an alpha 1-adrenergic antagonist with a binding affinity constant (Ki) of 58.3 nmol/l. both enantiomers of naftopidil revealed similar values, indicating no stereoselective inhibition of 3H-prazosin-binding. An alpha 1-adrenergic radiorecptor assay (RRA) was developed to determine receptor-binding material (parent compound and active metabolites) in the plasma of rats following single oral administration of naftopidil (50 mg/kg). The results indicate a rapid absorption. At the first sampling time (0.5 h) maximum concentration of receptor-binding material was measured. Terminal half-life was calculated with 16.7 h.