DETERMINATION OF ALPHA(1)-ADRENOCEPTOR ANTAGONISTS IN PLASMA BY RADIORECEPTOR ASSAY

A simple, rapid and sensitive radioreceptor assay (RRA) for the quanti fication of alpha(1)-adrenoceptor antagonists such as prazosin in plas ma is described. The method involves the use of an RRA based on [H-3]p razosin displacement in rat cerebral cortical membranes. The method is reliable, with intra-assay and inter-assay RSDs ranging from 5.9 to 9 .2%. The limit of detection is 0.2 (prazosin hydrochloride), 0.05 (tam sulosin hydrochloride) and 0.3 (bunazosin hydrochloride) pmol per assa y. Using this method the plasma levels of prazosin hydrochloride were determined in beagle dogs administered orally 2.39 mu mol kg(-1) of th is drug. The plasma levels of prazosin in beagle dogs are in good agre ement with those obtained using a high-performance liquid chromatograp hy (HPLC). This RRA proved to be applicable to the monitoring of plasm a prazosin levels in patients with essential hypertension and/or benig n prostatic hypertrophy receiving therapy with this drug with the ther apeutic dosage schedule. Thus, the concentrations of alpha(1)-adrenoce ptor antagonists in plasma can be adequately monitored by RRA as well as by HPLC.