Growth hormone: Synthesis and regulation

Growth hormone (GH) plays an essential role in the regulation of postnatal growth and metabolism through both direct and GH-IGF-1 axis-mediated mechanisms. GH action involves a complex interplay of endocrine, paracrine and autocrine signals that affect multiple tissues and organs. This review addresses the molecular and physiological fundamentals of GH secretion and action, as well as the multiple factors that modulate it, including central and peripheral signals, metabolic variables, physiological and pharmacological states. The relevance of GH receptor signaling and intracellular pathways involved in tissue response is discussed, as well as the mechanisms of hormone resistance that may arise in different clinical contexts. GH secretion, which is pulsatile, is subject to strict regulation by the hypothalamic-pituitary system, involving GHRH, somatostatin and ghrelin, together with negative feedback from GH and IGF-1. In addition, factors such as sleep, nutrition, stress, age or sex contribute significantly to its physiological variability. The implications of the somatotropic axis in pathological conditions such as GH deficiency, acromegaly or GH insensitivity syndromes are also explored.