Understanding Growth Hormone: The Key to Metabolism and Anabolism

Growth hormone (GH) is a crucial player secreted by the anterior pituitary gland, primarily produced by somatotroph cells that make up a notable portion of the pituitary's weight. Comprising 191 amino acids, GH has a unique structure that distinguishes it from non-primates, reflecting evolutionary changes in the GH/PRL gene family. This specificity is particularly important in medical applications, as recombinant human GH is now used to treat individuals with GH deficiency, highlighting its significance in health and growth.

The effects of GH are both metabolic and anabolic, working through various mechanisms to influence the body. The anabolic actions of GH are largely mediated by insulin-like growth factor I (IGF-I), a polypeptide produced in numerous tissues, especially the liver. IGF-I facilitates growth and development, acting either locally or systemically, and its production is regulated by a family of IGF-binding proteins. Notably, over 95% of serum IGF-I is bound to IGFBP-3 and acid-labile subunit, which are also stimulated by GH itself.

In terms of metabolism, GH has complex interactions with other hormones, particularly cortisol and insulin. Although GH promotes lipolysis and increases free fatty acid concentrations during fasting, it can also have a diabetogenic effect when present in excess. This means that GH tends to counteract insulin, leading to an increase in hepatic glucose output while simultaneously decreasing peripheral glucose utilization. The balance of these hormones is crucial in maintaining overall glucose homeostasis and preventing insulin resistance, especially when GH levels fluctuate.

Furthermore, GH plays a critical role in energy expenditure by elevating basal metabolic rates. This increase is achieved through various pathways, such as enhancing lean body mass and promoting fatty acid oxidation. The importance of GH is particularly pronounced during growth periods, where its output increases in response to body size, ensuring adequate development during childhood and adolescence.

Recent research has also highlighted the potential links between melatonin receptors, such as the type B receptor, and metabolic disorders like type 2 diabetes, particularly among shift workers who often experience disrupted endocrine rhythms. These findings suggest that understanding GH's role and interactions within the endocrine system could be vital for addressing various health issues, including metabolic syndromes and growth disorders.