Impact of Exercise Protocol and Fasting Status on Secretion of 20 and 22 Kda Human Growth Hormone

Presentation Number: SAT 434
Date of Presentation: April 1st, 2017

Michael Haenelt*, Andreas Lechner, Katharina Schilbach, Christina Gar, Rita Schwaiger and Martin Bidlingmaier
Klinikum der Universität München, München, Germany

Abstract

Introduction:

Human growth hormone (hGH) is secreted in response to a variety of stimuli including exercise and has an influence on glucose and lipid metabolism. GH secretion following pharmacological stimulation is reduced in obese subjects. We previously demonstrated that the ratio between 20kD and 22kD GH isoforms remains unchanged following pharmacological stimulation and short term exercise. The known impact of workload intensity and duration of a physical effort on glucose and lipid metabolism prompted us to study whether an acute bout of rigorous exercise and a prolonged submaximal exercise have different effects on GH isoform secretion.

Methods:

236 premenopausal, non-fasting women underwent a short, exhaustive cycle spiroergometry step-protocol (high intensity protocol, HIP: 15 minutes, mean workload 130 Watts, respiratory quotient (RQ) >1.1, mean maximum heart rate 170 bpm, mean peak VO2 corrected for fat free mass 39.95 ml O2/min).

A subset of the participants was also studied in a different protocol, applying a moderate intensity exercise over a longer time under fasted conditions (moderate intensity protocol, MIP: 45 min., 70% VO2 peak). In addition to cardiorespiratory variables, we analyzed the impact of age, body composition, oral contraceptive use (OC) and insulin sensitivity (ISI) on GH isoform response to exercise. GH isoforms were measured by specific immunoassays (22kD: IDS-iSYS GH CLIA, limit of quantification (LoQ) 0.05 ng/mL; 20kD: in-house FIA, LoQ 0.025 ng/mL).

Results:

In the HIP, baseline 22kD GH could be measured in 221/235 (94%) of the samples, while 20kD GH was >LoQ in only 24/235 (10.2%). Concentrations of 20kD and 22kD GH increased significantly with exercise and were highly correlated (p<0.0001) before and after exercise, with no significant change in the 20kDa/22kDa GH ratio induced by exercise (9.6 (SD 2.7) vs. 11.1 (SD 7.7), p=0.313). Neither peak GH nor % increase were correlated to cardiorespiratory variables, age, OC use or ISI (p>0.05 for all) Overweight and obese subjects tended to have a lower GH peak (not significant). In the MIP (fasted conditions), baseline 22kD GH tended to be higher than during HIP (non fasted, p<0,0001). Following MIP, GH isoforms showed the same parallel increase with exercise seen with HIP, with no change in the 20 kD/22kD ratio (15.42% vs 15.25% p>0.4842). However, baseline and post exercise resting 20kD/22kD ratio was significantly higher in the fasted MIP protocol compared to non-fasted HIP (mean 15.33% vs. mean 10.85%, p=0.0021).

Conclusion:

While the secretion of GH isoforms is not acutely affected by short term high intensity or a longer moderate intensity exercise protocol, the relative abundance of the 20Da isoform at rest was higher under the fasting conditions.

 

Nothing to Disclose: MH, AL, KS, CG, RS, MB