Response of plasma proenkephalin peptide F to exercise.

Plasma proenkephalin Peptide F immunoreactivity was measured in the plasma of endurance trained and untrained males at various exercise intensities. Significantly different levels were found between the two groups at rest and at 54% maximum oxygen consumption (VO2 max). Maximum levels were at 5 min of recovery for the untrained group and at 54% VO2 max and at recovery 5 min for the trained group. These data suggest an adaptation in the trained group fro the release of this peptide and further suggest it may play a role in recovery since the highest levels are following the termination of the exercise period.