Effect of 6 months of GH treatment on myosin heavy chain composition in GH-deficient patients

Objective: To investigate the effect of GH on myosin heavy chain (MHC) isof orm composition, physical fitness and body composition in GH-deficient (GHD ) patients. Design: Twenty-two GHD patients were randomized in a double blind manner an d half were treated with recombinant human GH (rhGH) and half were treated with placebo for 6 months. Twelve age-matched controls were also Included i n the study. Methods: MHC isoform composition in biopsies obtained from the vastus later alis muscle was determined using SDS-PAGE. Physical fitness was determined on a bicycle ergometer and body composition was determined using bioelectri cal impedance analysis. Results: More MHC IIX (28.9 +/- 4.1% and 10.0 +/- 3.1% in GHD and controls respectively (means +/- S.E.M.)) and less MHC I(36.2 +/- 2.4% and 51.7 +/- 3.9% in GHD and controls respectively (means +/- S.E.M.)) were present in t he GHD patients compared with the controls. No significant difference in th e amount of MHC IIA was detected. Linear regression was used to determine t he relationship between variables. There were no significant relationships between the concentration of insulin-like growth factor-I (IGF-I) or the bo dy composition and the MHC composition, Maximal oxygen uptake (VO(2)max) pe r kg body weight (BW) (litres/min per kg) correlated significantly with the amount of MHC I (r = 0.60) and MHC IIX (r = -0.72) but not with the amount of MHC IIA (r = 0.35). Treatment of GHD patients with rhGH for 6 months in creased the concentration of IGF-I, lean body mass and decreased fat mass b ut had no effect on MHC composition and physical fitness, Conclusions: We conclude that a major part of the differences in MHC compos ition between GHD patients and age-matched controls can be explained by var iation in physical fitness. The severity of the GHD and the body compositio n does not seem to be important for the MHC composition. Furthermore, treat ment with GH for 6 months does not affect MHC composition in GHD patients.