An ion exchange chromatography and radioimmunoassay procedure for measuring opioid peptides and substance P.

The measurements of peptides of the enkephalin, dynorphin and substance P systems is complicated by the number of possible precursor fragments and degradation products that might cross-react with the antisera. By using an ion-exchanger step before radioimmunoassay we can reduce the possibility that observed peptide levels are due to precursors or metabolites. The ion-exchanger method runs with good recovery and its main advantage is that many samples can be run in parallel. The recovery from the ion-exchanger was similar using two different homogenizing media, whereas the measured endogenous levels of [Met] and [Leu]enkephalin were 3-4 fold higher with 1M acetic acid than when a 1:1 MeOH/HCl mixture was used for tissue extraction.