Determination of β-Endorphin and Fragments Thereof in Human Plasma Using High-Performance Liquid Chromatography and a Multiple Radioimmunoassay System.

A method for the determination of β-endorphin and β-endorphin fragments in human plasma was developed. β-Endorphin-related peptides were extracted from plasma using octadecasilyl-silica cartridges. Extracts were subjected to re versed-phase high-performance liquid chromatography (HPLC). Extracts as well as HPLC column eluates were assayed using a multiple radioimmunoassay system; several antibodies directed against various distinct regions of the β-endorphin molecule were employed. Using this method, evidence for the presence of multiple β-endorphin fragments in the plasma of healthy young volunteers (under normal conditions) was obtained.