The availability of recombinant human GH and somatostatin analogs has resulted in widespread treatment for adults with GH deficiency (GHD) and those with GH excess (acromegaly). Despite being at opposite ends of the spectrum in terms of their GH/IGF-I axis, both of these populations experience overlapping somatic impairments. Adults with untreated GHD have low circulating levels of IGF-I that manifest as altered body composition with increased fat and reduced lean body and skeletal muscle mass. At the other end of the spectrum, adults with GH excess, who have elevated levels of IGF-I, also have altered body composition. Impairments that result from disorders of either GHD or GH excess are both associated with increased functional limitations, such as reduced ability to walk quickly for prolonged periods, and poorer health-related quality of life (HR-QoL). Adults with untreated GHD and GH excess both commonly complain of excessive fatigue that seems to be associated more with impaired aerobic than muscular performance.
Several studies have documented that administration of GH or somatostatin analogs to adults with GHD or GH excess, respectively, ameliorates abnormal biochemical profile and the associated somatic impairments. However, whether these improvements translate into improved physical function in adults with GHD or GH excess remains largely unknown, and their impact on HR-QoL controversial. Review of placebo-controlled trials to date suggests that GH and somatostatin analogs have greater effects on gas exchange and aerobic performance than as anabolic agents on skeletal muscle mass and function.
Future investigations should include dose-response studies to establish the optimal combination of pharmacological agents plus exercise required to improve not only biochemical markers but also physical function and HR-QoL in adults with GHD or GH excess.