Leptin is a peptide hormone involved in energy balance, appetite regulation, metabolic signaling, reproductive physiology, and communication between adipose tissue and the central nervous system. The hormone functions primarily as a long-term indicator of energy-storage status and helps coordinate adaptive responses to nutrient availability.
Leptin suppresses appetite, supports energy expenditure signaling, influences hypothalamic neuroendocrine pathways, and contributes to regulation of reproductive and metabolic physiology. The hormone also participates in immune communication, inflammatory signaling, glucose metabolism, and autonomic nervous-system regulation. Through these actions, leptin coordinates communication among adipose tissue, the hypothalamus, endocrine organs, and metabolic regulatory systems.
Leptin is produced mainly by adipocytes within white adipose tissue. The amount of circulating hormone generally reflects total body fat mass and long-term energy-storage availability. Smaller amounts may also be synthesized within the stomach, placenta, and additional endocrine-responsive tissues.
Production increases with greater adipose tissue mass and nutrient availability. Adipocytes continuously release leptin into circulation where it acts as an endocrine signal informing the brain about long-term energy reserves and metabolic status.
Leptin secretion is regulated mainly by adipose tissue mass, nutrient intake, insulin signaling, inflammatory pathways, and energy balance physiology. Fasting and caloric restriction reduce circulating leptin levels, while feeding and increased adiposity raise secretion.
The hormone acts through leptin receptor systems linked to JAK-STAT signaling, hypothalamic appetite-regulation pathways, autonomic signaling networks, and metabolic adaptation mechanisms. Leptin signaling influences neuropeptide systems controlling hunger, satiety, reproductive function, and energy expenditure. Through these integrated metabolic-endocrine systems, leptin coordinates appetite regulation, energy homeostasis, neuroendocrine communication, and long-term metabolic adaptation.
Leptin signals stored energy status and helps modulate hunger and metabolic rate.
