beta-endorphin (1-31) in the plasma of male volunteers undergoing physicalexercise

beta-Endorphin is an opioid peptide representing the C-terminal 31 amino ac id residue fragment of proopiomelanocortin (POMC). The release of beta-endo rphin from the pituitary into the cardiovascular compartment under physical or emotional stress has been frequently reported. However, besides beta-en dorphin (1-31), nine acetylated or non-acetylated beta-endorphin analogues exist - in addition to N-terminally elongated beta-endorphin derivatives su ch as beta-lipotropin (beta-LPH). Since conventional radioimmunoassays (RIA s) and even commercially available two site-RIAs pick up at least some of t hose beta-endorphin derivatives, only "beta-endorphin immunoreactive materi als" and not authentic beta-endorphin have been determined in those studies . We have developed a highly specific two site-RTA for beta-endorphin (1-31 ), which does not crossreact with all beta-endorphin derivatives known to o ccur as yet. Using this RIA as well as further assays for determination of beta-endorphin (1-31), beta-endorphin immunoreactive material (IRM), ACTH a nd Cortisol in the plasma of 14 volunteers upon intensive physical exercise , we found authentic beta-endorphin only in about 50% of the plasma samples , representing therein only a minor portion of the beta-endorphin IRM. (C) 2000 Elsevier Science Ltd. All rights reserved.