Stereospecific radioimmunoassay for propranolol isomers

Antisera against propranolol were produced in rabbits immunized with propranolol conjugated to bovine serum albumin. The antiserum against dl-propranolol recognized both d- and l-propranolol to the same degree. However, antiserum against l-propranolol was able to discriminate the l-propranolol selectively. The antisera were used to develop radioimmunoassays for dl-propranolol and l-propranolol. The assay can detect as little as 10 pg of propranolol. Metabolites of propranolol do not interfere with the assay unless concentrations are very high. Serum and heart levels of l-propranolol and the d-isomer were determined in the rat after i.v. injection (1 mg/kg) of dl-propranolol. l-Propranolol declines rapidly in the blood after the injection. Concomitantly, there is a rapid accumulation of l-propranolol by the heart. The d-form of propranolol remains in the blood and is metabolized rapidly as reflected by a shorter half-life (23.8 minutes) than the one found for l-propranolol (5.20 minutes).