Endocrine Abstracts

We previously have shown in a cohort of 236 non-fasted women that before and after a short high intensity exercise protocol (HIP) till exhaustion serum concentrations of 20 and 22 kD growth hormone (hGH) are highly correlated (P<0.0001). Although the GH response to exercise exhibited huge inter-individual differences, the 20 kD/22 kD-GH-ratio remained unchanged (9.6% vs 11.1%, P=0.313). A subgroup of the women was also studied under fasted conditions in a moderate intensity protocol, applying an exercise (70% VO2 peak) over a longer time (mean duration 45 min). In contrast to the HIP under non-fasted conditions, baseline and post exercise 20 kD/22 kD GH ratio were significantly higher in the fasted protocol (mean 15.33% vs. mean 10.85%, P=0.0021). To further investigate the impact of fasting and glucose intake on the 20 kD/22 kD-GH-ratio, we analyzed GH isoform secretion before and after an oral glucose tolerance test (OGTT, 75 g glucose) in a subset of the cohort (n=60; mean age 36 years (yr), range 20–44yr; BMI: mean 23, 2 kg/m²). GH isoforms were measured using the IDS-iSYS GH CLIA specific for 22 kD GH and an in-house IFMA for 20kD GH (LoQ 0.025 ng/ml), respectively. 20 kD GH was >LoQ of the assay in all subjects at baseline and in 86% 60 minutes after glucose ingestion. At baseline, fasting 20 kD/22 kD ratio in the subset was 12.9%. Ratio was not changed 60 min after glucose intake (12.3%; P>0.05). Due to the expected suppression of GH following glucose intake, after 120 min the 20 kD/22 kD-ratio could only be measured in 18.3% of the subjects, but no significant change in the abundance of 20 kD GH was observed (mean ratio 12.1%; P>0.05). In conclusion, the 20kD/22kD-GH ratio is lower in the non-fasted compared to the fasted state, both at baseline and following exercise. However, short-term oral glucose intake per se does not significantly influence the 20 kD/22 kD-GH ratio.