The Response of Molecular Isoforms of Growth Hormone to Acute Exercise in Trained Adult Males¹

Abstract

Circulating GH consists of multiple molecular isoforms, all derived from the one gene in nonpregnant humans. To assess the effect of a potent stimulus to pituitary secretion on GH isoforms, we studied 17 aerobically trained males (age, 26.9 +/- 1.5 yr) in a randomized, repeat measures study of rest vs. exercise. Exercise consisted of continuous cycle ergometry at approximately 80% of predetermined maximal oxygen uptake for 20 min. Serum was assayed for total, pituitary, 22-kDa, recombinant, non-22-kDa, 20-kDa, and immunofunctional GH. All isoforms increased during, peaked at the end, and declined after exercise. At peak exercise, 22-kDa GH was the predominant isoform. After exercise, the ratios of non-22 kDa/total GH and 20-kDa GH/total GH increased and those of recombinant/pituitary GH decreased. The disappearance half-times for pituitary GH and 20-kDa GH were significantly longer than those for all other isoforms. We conclude that 1) all molecular isoforms of GH measured increased with and peaked at the end of acute exercise, with 22-kDa GH constituting the major isoform in serum during exercise; and 2) the proportion of non-22-kDa isoforms increased after exercise due in part to slower disappearance rates of 20-kDa and perhaps other non-22-kDa GH isoforms. It remains to be determined whether the various biological actions of different GH isoforms impact on postexercise homeostasis.

Analysis of Major Isoforms of Human Growth Hormone before and after Intensive Physical Exercise

“…The relative increase was also more pronounced in men. These results agree with published data on the effect of physical activity on GH secretion into the blood [13]. GH release started 5-10 min after the start of physical activity and peaked after 15-30 min [5,8].…”

Responses of growth hormone aggregates to different intermittent exercise intensities

“…The commonly used radioimmunoassay (RIA) only seems to reveal a partial story about the kinetics of GH, since it simply measures the 22-kDa GH monomer. Different RIAs vary in results mainly as a result of differences between polyclonal and monoclonal antibodies and/or epitope specificity (Levin et al 1987;Strasburger et al 1989;Luthman et al 1990;Wallace et al 2001). In fact, Lewis et al (2000) suggest that the 22-kDa GH monomer may not even be the most abundant GH variant in the human circulation.…”

Effects of Acute and Chronic Exercise on Disulfide-Linked Growth Hormone Variants

“…that the structurc of the molecule drives ils ultimate function at the target tissue (26). For instance, size exclusion chromatography (12) or exclusion assays (28) have been used 10 demonstmte that exercise leads to the appearJnce of diffcrenl GH isofonns into the circulation. After chronic exercise training, these different GH isofom1S may offer a partial explanation for the disparate phenotypic outcomes as a result of differenI modes of chronic exercise tmining (20).…”