beta-Endorphin immunoreactive materials in human plasma determined by a multiple radioimmunoassay system

Extracts of plasma obtained from adult humans before and immediately after physical stress were subjected to high pressure liquid chromatography (HPLC); extracts or HPLC fractions, resp., were analysed for the presence of human beta-endorphin (beta H-endorphin) or fragments thereof by several radioimmunoassays using antibodies directed against the C-terminus and two "middle" regions of beta H-endorphin. Using an antibody ("Don Antonio") apparently directed against a beta H-endorphin fragment including positions 17 to 22 or somewhat adjacent regions, concentrations of beta H-endorphin immunoreactivity were found to be in the well-known range under normal conditions and to increase after physical stress. However, only a minor portion of this material proved to be identical with beta H-endorphin, whereas the major portion behaved like a smaller fragment thereof. In addition, high amounts of an immunoreactive material obviously containing a C-terminal sequence of beta H-endorphin were found, indicating the presence of an immunologically relevant beta H-endorphin fragment in the plasma.