Hormones are chemical messengers that circulate throughout the body, coordinating various functions. They are produced by glands and travel through the bloodstream to target cells and organs, where they elicit specific responses. Growth hormone (GH) is one such messenger, playing a broad role in the body’s overall functioning, including metabolic processes.
Understanding Growth Hormone
Growth hormone (GH), also known as somatotropin, is a protein hormone produced and released by the anterior pituitary gland, a small gland located at the base of the brain. While known for stimulating growth in children and adolescents, it remains active throughout adulthood. In adults, GH helps maintain body structure and participates in various metabolic activities, including carbohydrate and fat processing.
The Body’s Glucose Factories
The body has a sophisticated system for maintaining stable blood glucose levels (glucose homeostasis). A primary mechanism for this is gluconeogenesis, the creation of new glucose from non-carbohydrate sources. These sources include amino acids from proteins, glycerol from fats, and lactate. This pathway occurs mainly in the liver, with a smaller contribution from the kidneys. It is important when dietary carbohydrates are scarce, such as during fasting, prolonged exercise, or low-carbohydrate diets, ensuring a continuous glucose supply for tissues like the brain.
Growth Hormone’s Role in Glucose Production
Growth hormone directly influences liver cells to increase gluconeogenesis. This action involves GH binding to specific receptors on liver cells, initiating a signaling cascade. This signaling upregulates key enzymes involved in the gluconeogenic pathway, such as phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase), crucial for converting non-carbohydrate precursors into glucose. GH also promotes lipolysis, breaking down fats in adipose tissue and releasing free fatty acids. These free fatty acids serve as substrates for liver gluconeogenesis, contributing to glucose synthesis.
What Happens Next
The direct consequence of GH stimulating liver gluconeogenesis is an increase in glucose output from the liver into the bloodstream. This elevated glucose release contributes to a rise in overall blood glucose levels. The body responds by increasing insulin secretion to regulate circulating glucose. However, GH also reduces the sensitivity of peripheral tissues, like muscle and adipose tissue, to insulin, meaning these tissues may not take up glucose as efficiently. This combination of increased glucose production and reduced peripheral glucose uptake helps maintain blood glucose concentrations.
Why This Process Matters
GH-stimulated gluconeogenesis maintains blood sugar stability under specific physiological conditions. During fasting, when dietary glucose is unavailable, this process ensures the brain and other glucose-dependent tissues receive a continuous fuel supply. Similarly, during physical stress or prolonged exercise, when energy demands are high and glucose stores are depleted, GH promotes glucose production to sustain energy balance. This mechanism allows the body to adapt to varying nutritional states and energy requirements, contributing to overall metabolic homeostasis and survival.