Abstract

Epinephrine responses to insulin-induced hypoglycemia have indicated that athletes have a higher adrenal medullary secretory capacity than untrained subjects. This view was tested by an exercise protocol aiming at identical stimulation of the adrenal medulla in the two groups. Eight athletes (T) and eight controls (C) ran 7 min at 60 maximal O2 consumption (VO2max), 3 min at 100 VO2max and 2 min at 110 VO2max. Plasma epinephrine both at rest and at indentical relative work loads (110 VO2max: 8.73 +- 1.51 (T) vs. 3.60 +- 1.09 mmol/l (C)) was higher in T than in C. Norepinephrine, as well as heart rate, increased identically in the two groups, indicating identical sympathetic nervous activity. Lactate and glycerol were higher in T than in C after running. Glucose production peaked immediately after exercise and was higher in T than in C. Glucose disappearance increased less than glucose production and was identical in T and C. Accordingly plasma glucose increased, more in T than in C. In T glucose levels approached the renal threshold > 20 min postexercise. Glucose clearance increased less in T than in C during exercise and decreased postexercise to or below (T) basal levels, despite increased insulin levels. Long-term endurance training increases responsiveness of the adrenal medulla to exercise, indicating increased secretory capacity. During maximal exercise this may contribute to higher glucose production, lower clearance, more inaccurate glucoregulation, and higher lypolysis in T compared with C. Verf.-Referat