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A helical protein secreted by adipose tissue and acting on a receptor site in the ventromedial nucleus of the hypothalamus to curb appetite and increase energy expenditure as body fat stores increase. L. levels are 40% higher in women, and show a further 50% rise just before menarche, later returning to baseline levels; levels are lowered by fasting and increased by inflammation. [G. leptos, thin, + -in] Human genes encoding both l. (locus 7q31.3) and the l. receptor site (1p31) have been identified. Laboratory mice having mutations on the ob gene, which encodes l., become morbidly obese, diabetic, and infertile; administration of l. to these mice improves glucose tolerance, increases physical activity, reduces body weight by 30%, and restores fertility. Mice with mutations of the db gene, which encodes the l. receptor, also become obese and diabetic but do not improve with administration of l.. Although mutations in both the l. and l. receptor genes have been found in a small number of morbidly obese human subjects with abnormal eating behavior, the majority of obese persons do not show such mutations, and have normal or elevated circulating levels of l.. L. enhances insulin-mediated glucose transport into adipose cells in vitro. In preliminary trials, both lean and overweight persons have shown modest weight loss with daily subcutaneous injections of recombinant methionyl human l. over several months. All subjects followed weight-reduction diets during the trial period. Weight loss in some subjects receiving l. did not exceed that achieved by subjects receiving placebo, but when significant weight reduction occurred, it was proportionate to dosage. The immune deficiency seen in starvation may result from diminished l. secretion. Mice lacking the gene for l. or its receptor show impairment of T-cell function, and in laboratory studies l. has induced a proliferative response in human CD4 lymphocytes.
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lep·tin 'lep-tən n a peptide hormone that is produced by fat cells and plays a role in body weight regulation by acting on the hypothalamus to suppress appetite and burn fat stored in adipose tissue
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n.
a protein, produced by white fat cells in adipose tissue, that is involved in controlling the amount of white adipose tissue laid down in the body. It acts on the brain, possibly as a signal to regulate appetite or energy expenditure. Mutations in the ob gene, which codes for leptin, are responsible for some cases of obesity.
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lep·tin (lepґtin) a 167 amino acid adipocytokine that is part of a feedback loop that provides information to the brain about the state of nutrient stores. After secretion, it circulates in plasma and interacts with a specific receptor in the hypothalamus, decreasing food intake and increasing energy expenditure. It also increases insulin sensitivity, which is believed to result partly from its effect on the hypothalamus and partly from its action on peripheral tissues.Medical dictionary. 2011.