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Growth Hormone Replacement Therapy in Adults with Growth Hormone Deficiency Improves Maximal Oxygen Consumption Independently of Dosing Regimen or Physical Activity

Lilly Research Laboratories (M.L.H., A.Z., R.L.Q.), Eli Lilly and Co., Indianapolis, Indiana 46285; Departments of Human Services and Medicine (A.W.), University of Virginia, Charlottesville, Virginia 22908; Medical Service (A.R.H.), Veterans Affairs Palo Alto Health Care System, Palo Alto, California 94304; Stanford University (A.R.H.), Stanford, California 94305; Research and Medicine Services (G.R.M.), Veterans Affairs Puget Sound Health Care System, Tacoma, Tacoma, Washington 98493; and University of Washington School of Medicine (G.R.M.), Seattle, Washington 98195

Address all correspondence and requests for reprints to: George R. Merriam, M.D., Research (A-151), VA Puget Sound Health Care System, University of Washington School of Medicine, 9600 Veterans Drive SW, Tacoma, Washington 98493. E-mail: merriam{at}u.washington.edu.

Context: Several studies have demonstrated an improvement in aerobic exercise capacity with 6 months of GH replacement in adults with GH deficiency (GHD).

Objective: The objective of the study was to determine whether improvements in aerobic exercise capacity with GH treatment in adults with GHD are related to changes in physical activity or affected by the GH dosing regimen.

Design: This was a randomized, two-arm, parallel, open-label study.

Setting: The study was conducted at five academic medical centers with exercise physiology laboratories.

Subjects: Study subjects were adults (n = 29) with GHD due to hypothalamic-pituitary disease.

Interventions: The intervention was GH replacement therapy, administered either as a fixed body weight-based dosing regimen as an individualized dose titration regimen for 32 wk.

Main Outcome Measures: Maximal oxygen consumption (VO₂ max) and oxygen consumption (VO₂) at the lactate threshold, ventilatory threshold using a cycle ergometry protocol, and weekly energy expenditure (physical activity questionnaire), assessed at baseline and end point, were measured.

Results: In the group as a whole, VO₂ max increased significantly (by 9%) from baseline (19.1± 0.89 ml/kg·min) to end point (21.6 ± 1.23 ml/kg·min, P = 0.010). Compared with baseline, VO₂ max also changed significantly within the individualized dose titration regimen group (+2.5 ± 0.98 ml/kg·min, P =0.034) but not within the fixed body weight-based dosing regimen group (+1.2 ± 0.78 ml/kg·min, P = 0.15), although these changes from baseline were not significantly different between the two groups. VO₂ at lactate threshold, VO₂ at ventilatory threshold, and weekly energy expenditure also did not change.

Conclusions: GH replacement therapy in GH-deficient adults improved VO₂ max similarly with both dosing regimens, without any influence of physical activity. There was no effect on submaximal exercise performance.