Beta-endorphin and sprint training.

Male, Wistar rats were sprint trained using a high intensity, interval type, treadmill running protocol. Sprint training produced a significant decrease in plasma beta-endorphin levels. Conversely, animals who performed a high intensity acute run displayed significant increases in the concentration of plasma beta-endorphin which may be stress-related. Neither training nor acute running had any significant effect on the beta-endorphin levels of the pituitary, cortex, posterior or anterior hypothalamus.