Abstract des Autors

Six male non-endurance trained subjects (s) and six marathon runners (M) underwent graded treadmill exercise (T) and isoproterenol stimulation (I; 2 and 4 microg/min). Beta-adrenergic receptor density was additionally determined as the amount of 3H-Dihydroalprenolol (DHA) specifically bound on intact polymorphonuclear leucocytes. M showed the known training-dependent responses during T, such as lower heart rates, lactate levels, and plasma catecholamines at identical work loads, as well as higher VO2max than S. I-induced cardiac output increase was quite similar in both groups. Stroke volume, however, increased significantly in M and stayed constant in S. Lactate decreased (S), glucose increased significantly (M), glycerol increased similarly in both groups, FFA rise was less marked in S. I-induced stroke volume response (I) may be indicative of a more economic regulation of heart work in M than S. Lactate decrease and less marked FFA increase, as observed in S, may be the results of a somewhat higher cardiac energy demand, dependent on less economic heart work. Higher DHA-binding as observed in M, as well as stroke volume response and glucose increase, may be indicators of a training-dependent rise in sensitivity to catecholamines.