Response of plasma endorphins to running exercises in male and female endurance athletes.

We studied the responses of plasma concentrations of beta-endorphin, beta-lipotropin, and corticotropin to an exhaustive graded treadmill exercise, to an anaerobic treadmill exercise, and to a sub-maximal outdoor running exercise in 5 male and in 5 female endurance athletes. During the graded treadmill exercise, the mean plasma level (+/- SE) of beta-endorphin in men rose from 1.2 +/- 0.1 to 8.1 +/- 0.7 pmol.l-1, beta-lipotropin rose from 1.6 +/- 0.5 to 7.4 +/- 1.4 pmol.l-1, and corticotropin rose from 4.9 +/- 1.0 to 31 +/- 3.3 pmol.l-1. In women, the mean level of beta-endorphin rose from 1.2 +/- 0.2 to 8.2 +/- 1.8 pmol.l-1, beta-lipotropin rose from 1.4 +/- 0.1 to 8.1 +/- 2.0 pmol.l-1, and corticotropin rose from 3.3 +/- 0.4 to 28 +/- 7.9 pmol.l-1. Concentrations of endorphins and corticotropin increased significantly also during the anaerobic exercise test. In response to sub-maximal running exercise, no significant change was found. These results showed a relationship between the intensity of exercise and the secretion of pro-opiomelanocortin-related peptides, and there were no differences between the groups of trained men and women.