Endocrine Abstracts

Background/introduction: SUB:Pituitary – Clinical (Generously supported by IPSEN)We have previously shown that GH assessment during a standardized aerobic exercise of moderate intensity is a reliable test with high diagnostic accuracy in predicting severe GH deficiency (GHD) in adult individuals. However, these studies comprised comparably long exercise durations around 60 min or longer. To improve clinical applicability of exercise testing in the diagnosis of GHD a shorter test protocol would be preferable. The present study investigated the exercise-induced GH response in healthy athletes during a stepwise incremental VO₂ peak testing on a bicycle. We hypothesized that GH response would be smaller in bikers investigated on the bicycle compared with their running counterparts.

Methods: Nine endurance trained athletes volunteered to participate to this part of the study (seven males and two females), mean±S.D. age was 33±9.7 years. Participants were divided into two subgroups according to their prevalent exercise habits (bikers or runners). VO₂ peak testing was performed fasting in the morning on an electrically braked bicycle with gradually increased workload until exhaustion. Blood samples for GH were taken immediately before and after exercise, as well as at 15, 30, and 45 min after end of exercise. After testing for normal distribution GH values were compared by t-test.

Results: The mean±S.D. exercise duration was 11.0±1.5 min. Mean VO₂ peak was 54.6±5.83 ml/kg. For athletes mainly exercising on bike mean GH values were 1.97±1.9, 2.29±1.8, 3.33±0.8, 2.23±1.0 and 1.72±1.4 ng/ml before, directly after exercise and at 15, 30, and 45 min after the test respectively. The corresponding GH values in athletes whose exercise mainly consisted of running: were 2.51±3.3, 8.48±7.9, 12.50±7.5, 10.90±6.6, and 9.82±8.7 ng/ml. Peak GH was significantly lower in bikers compared with runners (3.59±0.8 vs 15.69±8.3, P=0.0244).

Conclusion: Based on these preliminary results in athletes a short stepwise exercise test increasing to exhaustion appears a promising test opportunity to provoke pituitary GH secretion under standardized conditions. However, when investigating individuals performing regular exercise the type of activity may be of importance in the choice of the test conditions. While bicycle testing induced a strong GH response in runners it resulted in considerably lower GH stimulation in bikers. This difference may be due to habituation effects resulting in a weaker stimulus. Whether testing bikers on a treadmill will revert this effect will have to be studied in a next step. Furthermore, we will now investigate short-term exercise induced GH response in GH deficient patient as well as in matched but sedentary controls.