Beta‐endorphin and adrenocorticotropin response to supramaximal treadmill exercise in trained and untrained males

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Abstract
Beta‐endorphin and adrenocorticotropin response to supramaximal treadmill exercise in trained and untrained males. Acta Physiol Scand130, 619–625. Received 18 March 1986, accepted 6 March 1987. ISSN 0001–6772. Institute of Medical Physiology B, University of Copenhagen, Denmark, Department of Human Kinetics, University of Wisconsin‐Milwaukee and Department of Physiology, Medical College of Wisconsin, and Departments of Clinical Chemistry and Neuromedicine, Gentofte Hospital, Denmark. The response of plasma β‐endorphin (β‐EP) and adrenocorticotropin (ACTH) was studied in seven well‐trained (T) young endurance athletes and seven untrained (UT) age‐ and weightdmatched 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 (41 °C) hand vein. Plasma β‐EP was measured by radio‐immunoassay (RIA) which incorporated an antibody that did not cross‐react (< 1.5%) with β‐lipotropin. Plasma β‐EP was similar between groups at rest (T = 4.3±0.8 fmol ml‐1, mean ± SE, UT = 3.3 ± 0.6 fmol ml‐1) and did not change at the 60%±o2max 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‐1, P 0.05 for between group differences). This between group difference persisted I rnin after exercise when the highest β‐EP levels were reached (T = 18.7 ± 4.7 and UT = 12.8 ± 3.1 fmol ml‐l, P 0.05). Plasma ACTH responses were similar to β‐EP with the highest values (T = 61.5 ±7.2, UT = 45.7 ± 6.8 fmol ml‐1, P 0.05 for between group differences) occurring at I min post‐exercise. A positive correlation, r = 0.85, P 0.05, was found between β‐EP and ACTH using the I rnin post‐exercise values. The enhanced response of β‐EP and ACTH in T may indicate a training‐induced adaptation which increases the response capacity to extreme levels of stress.