Endocrine Control and Regulation of Growth Hormone: An Overview

Abstract

The control of growth hormone (GH) production is complex, partly because GH serves both metabolic and anabolic roles. GH exerts potent anti-insulin effects at hepatic and peripheral sites and increases fat mobilization and lipolysis. IGF-I, a critical growth factor induced by GH, is likely responsible for most anabolic (on lean mass and bone mineralization) and growth-promoting (on growth plate) activities of GH, which also requires sufficient energy stores. GH secretion is regulated by hypothalamic growth hormone-releasing hormone (GHRH) and somatostatin interacting with circulating hormones, metabolic regulators, neurotransmitters, and additional modulatory peptides at the level of both the pituitary and the hypothalamus. Age, puberty, gender, sleep, exercise, food intake, and body composition are physiological determinants of GH secretion. Numerous hormones (ghrelin, sex steroids, glucocorticoids, thyroid hormones, insulin, glucagon, leptin, GH itself, and IGF-1) and metabolic regulators (glucose, amino acids, free fatty acids) control GH. “Normal” GH secretion covers a broad range of GH concentrations, and the definition of thresholds for GH deficiency following stimulation tests or integrated GH concentration measurement over 24 h proves to be difficult. There is no gold standard for GHD diagnosis, which relies on medical history, auxology, IGF-1/IGFBP3 measurements, GH provocative tests, and magnetic resonance imaging findings.