The response of molecular isoforms of growth hormone to acute exercise in trained adult males

Circulating GH consists of multiple molecular isoforms, all derived from th e one gene in nonpregnant humans. To assess the effect of a potent stimulus to pituitary secretion on GH isoforms, we studied 17 aerobically trained m ales (age, 26.9 +/- 1.5 yr) in a randomized, repeat measures study of rest vs. exercise. Exercise consisted of continuous cycle ergometry at approxima tely 80% of predetermined maximal oxygen uptake for 20 min. Serum was assay ed for total, pituitary, 22-kDa, recombinant, non-22-kDa, 20-kDa, and immun ofunctional GH. All isoforms increased during, peaked at the end, and decli ned 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 disappearanc e 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 2 2-kBa GH constituting the major isoform in serum during exercise; and 2) th e 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 isofo rms. It remains to be determined whether the various biological actions of different GH isoforms impact on postexercise homeostasis.