Decreases in resting plasma beta-endorphin/-lipotropin after endurance training

The purpose of the present study was to investigate changes in the resting plasma beta-endorphin/-lipotropin (beta E/beta-LPH) concentration that may occur with exercise training. A treatment group (N = 10) of previously sedentary, psychologically normal, and medically healthy middle-aged men trained for 4 months in a structured fitness program. The treatment group was compared with two age-matched groups: a jogger group (N = 10) and a sedentary group (N = 10). Venous blood was collected in the early morning after the subjects had been fasting for at least 12 h. The subjects were also resting at the time of blood collection. Resting plasma beta E/beta-LPH (measured by radioimmunoassay) decreased (P less than 0.05) following the 4 months of exercise training in the treatment group, from 11.01 +/- 1.62 (SE) to 7.22 +/- 0.99 pmol.1-1. The jogger and sedentary groups demonstrated no changes in the resting plasma beta E/beta-LPH concentration following the 4 months. Aerobic fitness, measured by the maximal oxygen uptake (VO2max), increased (P less than 0.01) from 36.56 +/- 2.58 (SE) to 44.85 +/- 1.34 ml.kg-1.min-1 in the treatment group after the 4 months of training. There were no changes in VO2max for either the jogger group or the sedentary group following the 4 months. In conclusion, beta E/beta-LPH in the plasma of resting middle-aged men appeared to be decreased after 4 months of aerobic training.