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.