Leptin

Leptin is a hormone secreted from the adipose tissue whose levels in blood reflect the total adipose stores. It acts on leptin receptors in the hypothalamus to regulate energy balance. Absence of leptin or its receptors in the hypothalamus triggers a large number of responses, including increased appetite and reduced metabolic rate, that act to increase adiposity. In the presence of adequate nutritional resources, however, such a condition produces massive obesity. Among the most important targets of leptin are the hypothalamic neurons expressing proopiomelanocorticotropin (POMC), Agouti-related peptide (AgRP)/neuropeptide Y (NPY), steroidogenic factor-1 (Sf1), or melanin-concentrating hormone (MCH). Clinical trials show that leptin treatment fails to reduce obesity. Leptin may be more useful to treat the neuroendocrine impairments associated with lipodystrophy, but this has yet to be demonstrated.