- Growth hormone (GH), also known as somatotropin, is a peptide hormone produced by the anterior pituitary gland. It plays a central role in regulating growth, metabolism, and body composition throughout life, but is especially critical during childhood and adolescence.
- GH stimulates the growth of bones and tissues, promotes protein synthesis, increases muscle mass, and influences the metabolism of carbohydrates and fats. Its secretion is regulated by the hypothalamus through two primary hormones: growth hormone-releasing hormone (GHRH), which stimulates GH release, and somatostatin, which inhibits it.
- The biological actions of GH are mediated directly through GH receptors on target tissues and indirectly through the stimulation of insulin-like growth factor 1 (IGF-1), primarily produced in the liver. IGF-1 is a key mediator of GH’s growth-promoting effects and acts in an endocrine, paracrine, and autocrine manner to stimulate the proliferation and differentiation of chondrocytes in growth plates, leading to longitudinal bone growth. In addition, GH promotes protein anabolism by enhancing amino acid uptake and increasing protein synthesis in various tissues, especially muscles, making it crucial for muscle development and repair.
- Metabolically, GH exerts lipolytic effects, breaking down triglycerides in adipose tissue and increasing free fatty acids in the bloodstream, which serve as an energy source. It also affects carbohydrate metabolism, often antagonizing insulin’s effects by decreasing glucose uptake in peripheral tissues and increasing hepatic gluconeogenesis, which can result in reduced insulin sensitivity. This complex interplay underscores GH’s dual anabolic (protein synthesis and growth) and catabolic (lipid breakdown and glucose conservation) functions.
- The secretion of GH is pulsatile, with the highest peaks occurring during deep sleep, particularly in the early part of the night. GH levels are influenced by several physiological factors, including age, sex, sleep, stress, exercise, and nutritional status. For example, GH secretion is highest during puberty and declines with age. Exercise and fasting typically stimulate GH release, whereas obesity and hyperglycemia suppress it.
- Abnormalities in GH production can lead to significant health disorders. GH deficiency in children results in growth retardation and short stature (pituitary dwarfism), while in adults it may cause decreased muscle mass, fatigue, poor bone density, and adverse changes in lipid metabolism. Conversely, excess GH leads to gigantism in children (before epiphyseal plate closure) and acromegaly in adults, characterized by enlarged hands, feet, jaw, and soft tissue overgrowth, as well as metabolic complications like insulin resistance and cardiovascular disease.
- Clinically, recombinant human growth hormone (rhGH) is used to treat GH deficiency, Turner syndrome, chronic kidney disease, Prader-Willi syndrome, and other growth-related disorders. It is also sometimes misused as a performance-enhancing drug in athletics or for anti-aging purposes, although such uses carry health risks and are generally not medically approved.
