Which hormone is primarily responsible for stimulating metabolic activity?

Thyroxine, also known as T4, is a hormone produced by the thyroid gland and plays a critical role in regulating metabolism. Its primary function is to increase the basal metabolic rate, which is the rate at which the body uses energy at rest. By enhancing the metabolic processes of cells, thyroxine contributes to the overall energy expenditure of the body. This includes stimulating the oxidation of glucose and fatty acids to produce ATP, thereby influencing how the body converts food into energy.

Other hormones, such as testosterone, insulin-like growth factor (IGF-1), and glucagon, also have important roles in metabolism but in more specific contexts. For example, testosterone is involved in muscle growth and development, IGF-1 promotes growth and has an anabolic effect, and glucagon primarily serves to increase blood glucose levels by promoting glucose release from the liver. However, when it comes to stimulating overall metabolic activity in a broad sense, thyroxine is the key player.