The effect of running on plasma β-endorphin

Plasma β-endorphin immunoactivity was measured by RIA in 26 trained long distance runners on 35 occasions before and after running. Mean total β-endorphin immunoactivity increased from 11.8 ± 1.8 (SEM) to 17.6 ± 3.1 pg/m1 in 20 runners after an easy run ( p = .067), and from 8.2 ± 1.03 to 28.0 ± 6.3 pg/ m1 in 15 runners after a strenuous run (p = .008). Total β-endorphin immunoactivity in the plasma extracts of 7 runners before and after the strenuous run was further characterized by Sephadex G-50 chromatography in order to separate β-endorphin from corssreacting β-lipotropin (β-LPH). A rise in β-endorphin and β-LPH concentrations after running was noted in 5 out of 7 runners.