GH Administration Changes Myosin Heavy Chain Isoforms in Skeleta

GH Administration Changes Myosin Heavy Chain Isoforms in Skeletal Muscle But Does Not Augment Muscle Strength or Hypertrophy, Either Alone or Combined with Resistance Exercise Training in Healthy Elderly Men

The Journal of Clinical Endocrinology & Metabolism 2002; 87: 513-523
Kai Henrik Wiborg Lange, Jesper Løvind Andersen, Nina Beyer, Fredrik Isaksson, Benny Larsson, Michael Højby Rasmussen, Anders Juul, Jens Bülow and Michael Kjær

GH administration, either alone or combined with resistance exercise training (RT), has attracted interest as a means of increasing muscle mass and strength in the elderly. In the present study, 31 healthy, elderly men [age, 74 ± 1 yr (mean ± SEM)] were assigned to either RT [3 sessions/wk, 3-5 sets of 8-12 repetition maximum (RM)/session] placebo (n = 8), RT GH (n = 8), GH (n = 8), or placebo (n = 7) in a randomized, placebo-controlled, double-blinded (RT placebo and RT GH) or single-blinded (GH or placebo) design. Measurements of: 1) isokinetic quadriceps muscle strength; 2) quadriceps muscle power; 3) quadriceps muscle fiber type, size, and myosin heavy chain (MHC) composition; 4) quadriceps cross-sectional area (CSA) [nuclear magnetic resonance imaging (NMRI)]; 5) body composition (dual-energy x-ray absorptiometry scanning); and 6) GH-related serum markers were performed at baseline and after 12 wk. The final GH dose was 1.77 ± 0.18 IU·d-1 (7.2 ± 0.8 µg·kg-1·d-1). GH alone had no effect on isokinetic quadriceps muscle strength, power, CSA, or fiber size. However, a substantial increase in MHC 2X isoform was observed with GH administration alone, and this may be regarded as a change into a more youthful MHC composition, possibly induced by the rejuvenating of systemic IGF-I levels. RT placebo caused substantial increases in quadriceps isokinetic strength, power, and CSA; but these RT induced improvements were not further augmented by additional GH administration. In the RT GH group, there was a significant decrease in MHC 1 and 2X isoforms, whereas MHC 2A increased. RT, therefore, seems to overrule the changes in MHC composition induced by GH administration alone. Changes in body composition confirmed previous reports of decreased fat mass, increased fat-free mass, and unchanged bone mineral content with GH administration. A high incidence of side effects was reported. Our results do not support a role for GH as a means of increasing muscle strength or mass, either alone or combined with RT, in healthy elderly men; although GH administration alone may induce changes in MHC composition.