Radioreceptor assay for ergot derivatives, transdihydrolisuride and lisuride, in biological fluids

The development of a sensitive radioreceptor assay (RRA) for transdihydrolisuride (TDHL) and lisuride, as well as the synthesis of tritiated TDHL, is described. The method is based upon the competition between 3H TDHL and TDHL or lisuride for rat brain dopaminergic receptors. Linear calibration graphs were obtained in the range of 0.2-9 pmol for an ergot derivative. Relative affinities of the main metabolites, deethylated and dideethylated on the urea part of the molecule are 3.6% and 1.5%, respectively, as compared to the parent drug. To verify the method, plasma levels of TDHL were determined in rats after oral administration.