Adrenocorticotropic hormone (ACTH), β-endorphin immunoreactive material (β-endorphin IRM), and authentic β-endorphin (1 - 31) have been determined in the plasma of 23 volunteers undergoing anaerobic exercise on a rowing ergometer. The volunteers had different histories of training from occasional physical activities up to intensive preparation for international rowing competitions. ACTH and β-endorphin-IRM were determined using commercially available immunometric assays; for determination of β-endorphin (1 - 31) a highly specific two-site fluid phase immunoprecipitation radioimmunoassay was developed, which did not cross-react with any β-endorphin derivative or any other opioid peptide tested. In agreement with reports from the literature ACTH and β-endorphin-IRM concentrations in the plasma rose upon anaerobic exercise in all 23 subjects; this increase in the ACTH and β-endorphin IRM levels was significantly correlated with the increase of lactate levels observed upon anaerobic exercise. Authentic β-endorphin (1 - 31) was only found in two plasma samples containing minor concentrations of the peptide. We conclude that the β-endorphin immunoreactive material released into blood under anaerobic exercise is identical with authentic β-endorphin (1 - 31) only to a minor extent and thus should not be called “β-endorphin”. The major part of the material in fact released into the blood upon anaerobic exercise is probably identical with β-lipotropin and further components so far unknown.
Physical stress, opioid peptides, ACTH, lactate, fluid phase immunoprecipitation two-site radioimmunoassay.
