Obesity and the Growth Hormone Axis

Growth hormone (GH), as its name implies, promotes growth and alters nutrient metabolism through direct activation of the GH receptor (GHR) on target tissues. GH also indirectly regulates growth and nutrient metabolism by altering production of additional factors. One of the most important secondary effects of GH action is insulin-like growth factor-1 (IGF-1). Many of the growth-promoting activities that result from GH occur via GH-stimulated IGF-1 production. Due to the strong link between GH and IGF-1, they are often referred to collectively as the GH/IGF-1 axis. The GH/IGF-1 axis has anabolic effects on most tissues, including the heart, liver, kidneys, and intestines; however, GH – but not IGF-1 – has a dramatic catabolic effect on adipose tissue (AT). This chapter will focus mainly on GH, describe the clinical conditions and mouse lines with alterations in this axis along with their adiposity phenotype, and conclude by considering the role and therapeutic use of GH in obesity.