Effect of blood loss on the plasma level of whole peptides and their fractions at rest and during exertion and restitution.

The plasma level of peptides and their fractions was investigated in 12 male voluntary blood donors aged 19-23 years at rest, during exercise and restitution before and 1 and 24 h after blood withdrawal. In each test the subjects exercised on Monark's cycle ergometer under loads producing a heart rate acceleration up to 170/min (Physical Working Capacity -- PWC 170). Blood loss produced a non-significant decrease in the plasma peptide level. During exercise the levels increased significantly both before (P less than 0.001) as well as 1 h and 24 h after blood loss (P less than 0.025). About one half of the increase was due to haemoconcentration. During restitution the levels were not significantly different from the initial values. Blood loss gave rise to a significant increase in the level of fractions of a molecular weight exceeding 3500 while the concentration of fractions of 1500-3500 molecular weight decreased. The changes in the peptide fractions were slightly different in the case of exercise performed after blood loss from those observed before blood loss. This applies first of all to fractions with a molecular weight below 750 whose concentration decreased during exercise performed after, and increased before, blood loss.