A radioreceptor assay for propranolol

Publisher Website
Google Scholar
Abstract
A radioreceptor assay for the measurement of propranolol levels in human subjects is described. The assay is based upon competition between the radiolabeled β‐adrenergic inhibitor [125I]iodohydroxybenzylpindolol and propranolol for specific beta receptor sites in turkey erythrocyte plasma membranes. The radioreceptor assay is extremely sensitive, specific, and technically adaptable to processing clinical samples. Propranolol in serum is quantitatively extracted into ethyl acetate and, after the organic phase is reduced to dryness, reconstituted in aqueous assay buffer. Propranolol levels as low as 0.25 to 0.5 ng/ml can be detected and maximal sensitivity occurs at a concentration of 2.4 ± 0.2 ng/ml. The assay demonstrates specificity for biologically active metabolites of propranolol as well and therefore, with modifications, has the potential of providing a composite index of circulating β‐adrenergic inhibitory activity. Nonactive propranolol metabolites, d‐isomers, and the catecholamines do not significantly interfere in the assay. Thirty clinical samples containing a wide spectrum of propranolol concentrations were analyzed by radioreceptor assay and then compared with values obtained by high‐pressure liquid chromatography (HPLC) or by radioimmunoassay. The coefficients of correlation, r, between the radioreceptor assay and these other two methods were +0.91 and +0.85, respectively (p < 0.01). These observations establish the characteristics and the clinical feasibility of the radioreceptor assay for propranolol and suggest that it will be useful in further elucidating the kinetics of propranolol in human subjects.