Abstract

The response of plasma beta-endorphin (beta-EP) and adrenocorticotropin (ACTH) was studied in seven well-trained (T) young endurance athletes and seven untrained (UT) age- and weight-matched males during treadmill exercise. Subjects ran continuously for 7 min at 60 VO2max, 3 min at 100 VO2max and 2 min at 110 VO2max. Arterialized blood was obtained periodically from a cannulated heated hand vein. Plasma beta-EP was measured by radio-immunoassay (RIA) which incorporated an antibody that did not cross-react with beta-lipotropin. Plasma beta-EP was similar between groups at rest and did not change at the 60 VO2max stage. Beta-endorphin significantly increased at 100 VO2max with both groups responding similarly. A further increase occurred at 110 VO2max (T=10.8+/-2.0 and UT = 6.6+/-1.0 fmol/ml, P < 0.05 for between group differences). This between group difference persisted 1 min after exercise when the highest beta-EP levels were reached. Plasma ACTH responses were similar to beta-EP with the highest values (T = 61.5 plus minus 7.2, UT = 45.7 plus minus 6.8 fmol/ml, P < 0.05 for between group differences) occuring at 1 min post-exercise. A positive correlation, r = 0.85, P < 0.05, was found between beta-EP and ACTH using the 1 min post-exercise values. The enhanced response of beta-EP and ACTH in T may indicate a training-induced adaptation which increases the response capacity to extreme levels of stress. Verf.-Referat