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 Leptin is a 143 amino acid peptide
hormone and is the product of the Ob gene. It is thought
to play an important role in lowering food intake and
body weight and is of great interest to those researching
the causes of obesity. It has revealed adipose tissue as
an important endocrine organ. Leptin is secreted by
adipose cells and acts at the hypothalamus, which has an
abundance of leptin receptors as well as expressing
various neuropeptides influencing food intake.
The effects of leptin are exerted by expression of the
anabolic neuropeptides, neuropeptide Y and agouti-related
peptide along with co-expression of pro-opiomelanocortin,
the precursor of the catabolic neuropeptide, a-MSH. CRH,
a major anorectic neuropeptide, is also believed to play
a role in regulation of food intake and energy
homeostasis, although it is not though that CRH produced
in response to leptin interacts with the
pituitary-adrenocortical axis.
In experiments using rodents and humans, leptin is found
to circulate in plasms at concentrations directly related
to adipose tissue mass. In another study, the ob/ob
mouse, which has a mutation in the leptin gene and cannot
synthesise leptin, displays progound obesity. This is
reversed on treatment with leptin. Findings such as these
have led to much interest in this area, although the
exact mechanism of leptin action in the brain have yet to
be clarified. |
