Which of the following hormones decreases appetite?

Leptin is a key hormone in the regulation of appetite and energy balance. It is produced predominantly by adipose (fat) tissue and plays a crucial role in signaling to the brain about the body's energy stores. When fat stores are adequate or high, leptin levels increase, leading to a reduction in appetite and an increase in energy expenditure. This hormonal signaling helps to maintain body weight by promoting feelings of satiety, which can prevent overeating.

In contrast, other hormones such as ghrelin, which is secreted by the stomach, stimulate appetite and promote food intake. Similarly, neuropeptide Y, a neurotransmitter found in the brain, is involved in stimulating hunger. Norepinephrine can have various effects on metabolism and energy expenditure but is not primarily responsible for lowering appetite.

Thus, understanding the role of leptin highlights its importance in appetite regulation and energy homeostasis, making it the correct answer in this context.