Characterization of growth hormone disulfide-linked molecular isoforms during post-exercise release vs nocturnal pulsatile release reveals similar milieu composition.

OBJECTIVE: To characterize the influence of mode (aerobic/resistance) and volume of exercise (moderate/high) on circulating GH immediately post-exercise as well as following the onset of sleep.

DESIGN: This study used repeated measures in which subjects randomly completed 5 separate conditions: control (no exercise), moderate volume resistance exercise (MR), high-volume resistance exercise (HR), moderate volume aerobic exercise (MA), and high volume aerobic exercise (HA).

METHODS: Subjects had two overnight stays on each of the 5 iterations. Serial blood draws began as soon as possible after the completion of the exercise session. Blood was obtained every 20 min for 24-h. GH was measured using a chemiluminescent immunoassay. Pooled samples representing post exercise (PE) and first nocturnal pulse (NP) were divided into two aliquots. One of these aliquots was chemically reduced by adding 10 mM glutathione (GSH) to break down disulfide-linked aggregates.

RESULTS: No differences were observed when pooling GH response at post-exercise (2.02 ± 0.21) and nocturnal pulse (2.63 ± 0.51; p = .32). Pairwise comparisons revealed main effect differences between controls (1.19 ± 0.29) and both MA (2.86 ± 0.31; p = .009) and HA (3.73 ± 0.71; p = .001). Both MA (p = .049) and HA (p = .035) responses were significantly larger than the MR stimulus (1.96 ± 0.28). With GSH reduction, controls significantly differed from MA (p = .018) and HA (p = .003) during PE, but only differed from HA (p = .003) during NP.

CONCLUSIONS: This study demonstrated similar GH responses to exercise and nocturnal pulse, indicating that mode and intensity of exercise does not proportionately affect GH dimeric isoform concentration.